// SPDX-License-Identifier: GPL-2.0

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/sched/mm.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/prefetch.h>
#include <linux/fsverity.h>
#include "extent_io.h"
#include "extent-io-tree.h"
#include "extent_map.h"
#include "ctree.h"
#include "btrfs_inode.h"
#include "bio.h"
#include "locking.h"
#include "backref.h"
#include "disk-io.h"
#include "subpage.h"
#include "zoned.h"
#include "block-group.h"
#include "compression.h"
#include "fs.h"
#include "accessors.h"
#include "file-item.h"
#include "file.h"
#include "dev-replace.h"
#include "super.h"
#include "transaction.h"

static struct kmem_cache *extent_buffer_cache;

#ifdef CONFIG_BTRFS_DEBUG
static inline void btrfs_leak_debug_add_eb(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        unsigned long flags;

        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        list_add(&eb->leak_list, &fs_info->allocated_ebs);
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

static inline void btrfs_leak_debug_del_eb(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        unsigned long flags;

        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        list_del(&eb->leak_list);
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
{
        struct extent_buffer *eb;
        unsigned long flags;

        /*
         * If we didn't get into open_ctree our allocated_ebs will not be
         * initialized, so just skip this.
         */
        if (!fs_info->allocated_ebs.next)
                return;

        WARN_ON(!list_empty(&fs_info->allocated_ebs));
        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        while (!list_empty(&fs_info->allocated_ebs)) {
                eb = list_first_entry(&fs_info->allocated_ebs,
                                      struct extent_buffer, leak_list);
                btrfs_err(fs_info,
                       "buffer leak start %llu len %u refs %d bflags %lu owner %llu",
                       eb->start, eb->len, refcount_read(&eb->refs), eb->bflags,
                       btrfs_header_owner(eb));
                list_del(&eb->leak_list);
                WARN_ON_ONCE(1);
                kmem_cache_free(extent_buffer_cache, eb);
        }
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}
#else
#define btrfs_leak_debug_add_eb(eb)                     do {} while (0)
#define btrfs_leak_debug_del_eb(eb)                     do {} while (0)
#endif

/*
 * Structure to record info about the bio being assembled, and other info like
 * how many bytes are there before stripe/ordered extent boundary.
 */
struct btrfs_bio_ctrl {
        struct btrfs_bio *bbio;
        /* Last byte contained in bbio + 1 . */
        loff_t next_file_offset;
        enum btrfs_compression_type compress_type;
        u32 len_to_oe_boundary;
        blk_opf_t opf;
        /*
         * For data read bios, we attempt to optimize csum lookups if the extent
         * generation is older than the current one. To make this possible, we
         * need to track the maximum generation of an extent in a bio_ctrl to
         * make the decision when submitting the bio.
         *
         * The pattern between do_readpage(), submit_one_bio() and
         * submit_extent_folio() is quite subtle, so tracking this is tricky.
         *
         * As we process extent E, we might submit a bio with existing built up
         * extents before adding E to a new bio, or we might just add E to the
         * bio. As a result, E's generation could apply to the current bio or
         * to the next one, so we need to be careful to update the bio_ctrl's
         * generation with E's only when we are sure E is added to bio_ctrl->bbio
         * in submit_extent_folio().
         *
         * See the comment in btrfs_lookup_bio_sums() for more detail on the
         * need for this optimization.
         */
        u64 generation;
        btrfs_bio_end_io_t end_io_func;
        struct writeback_control *wbc;

        /*
         * The sectors of the page which are going to be submitted by
         * extent_writepage_io().
         * This is to avoid touching ranges covered by compression/inline.
         */
        unsigned long submit_bitmap;
        struct readahead_control *ractl;

        /*
         * The start offset of the last used extent map by a read operation.
         *
         * This is for proper compressed read merge.
         * U64_MAX means we are starting the read and have made no progress yet.
         *
         * The current btrfs_bio_is_contig() only uses disk_bytenr as
         * the condition to check if the read can be merged with previous
         * bio, which is not correct. E.g. two file extents pointing to the
         * same extent but with different offset.
         *
         * So here we need to do extra checks to only merge reads that are
         * covered by the same extent map.
         * Just extent_map::start will be enough, as they are unique
         * inside the same inode.
         */
        u64 last_em_start;
};

/*
 * Helper to set the csum search commit root option for a bio_ctrl's bbio
 * before submitting the bio.
 *
 * Only for use by submit_one_bio().
 */
static void bio_set_csum_search_commit_root(struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_bio *bbio = bio_ctrl->bbio;

        ASSERT(bbio);

        if (!(btrfs_op(&bbio->bio) == BTRFS_MAP_READ && is_data_inode(bbio->inode)))
                return;

        bio_ctrl->bbio->csum_search_commit_root =
                (bio_ctrl->generation &&
                 bio_ctrl->generation < btrfs_get_fs_generation(bbio->inode->root->fs_info));
}

static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_bio *bbio = bio_ctrl->bbio;

        if (!bbio)
                return;

        /* Caller should ensure the bio has at least some range added */
        ASSERT(bbio->bio.bi_iter.bi_size);

        bio_set_csum_search_commit_root(bio_ctrl);

        if (btrfs_op(&bbio->bio) == BTRFS_MAP_READ &&
            bio_ctrl->compress_type != BTRFS_COMPRESS_NONE)
                btrfs_submit_compressed_read(bbio);
        else
                btrfs_submit_bbio(bbio, 0);

        /* The bbio is owned by the end_io handler now */
        bio_ctrl->bbio = NULL;
        /*
         * We used the generation to decide whether to lookup csums in the
         * commit_root or not when we called bio_set_csum_search_commit_root()
         * above. Now, reset the generation for the next bio.
         */
        bio_ctrl->generation = 0;
}

/*
 * Submit or fail the current bio in the bio_ctrl structure.
 */
static void submit_write_bio(struct btrfs_bio_ctrl *bio_ctrl, int ret)
{
        struct btrfs_bio *bbio = bio_ctrl->bbio;

        if (!bbio)
                return;

        if (ret) {
                ASSERT(ret < 0);
                btrfs_bio_end_io(bbio, errno_to_blk_status(ret));
                /* The bio is owned by the end_io handler now */
                bio_ctrl->bbio = NULL;
        } else {
                submit_one_bio(bio_ctrl);
        }
}

int __init extent_buffer_init_cachep(void)
{
        extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
                                                sizeof(struct extent_buffer), 0, 0,
                                                NULL);
        if (!extent_buffer_cache)
                return -ENOMEM;

        return 0;
}

void __cold extent_buffer_free_cachep(void)
{
        /*
         * Make sure all delayed rcu free are flushed before we
         * destroy caches.
         */
        rcu_barrier();
        kmem_cache_destroy(extent_buffer_cache);
}

static void process_one_folio(struct btrfs_fs_info *fs_info,
                              struct folio *folio, const struct folio *locked_folio,
                              unsigned long page_ops, u64 start, u64 end)
{
        u32 len;

        ASSERT(end + 1 - start != 0 && end + 1 - start < U32_MAX);
        len = end + 1 - start;

        if (page_ops & PAGE_SET_ORDERED)
                btrfs_folio_clamp_set_ordered(fs_info, folio, start, len);
        if (page_ops & PAGE_START_WRITEBACK) {
                btrfs_folio_clamp_clear_dirty(fs_info, folio, start, len);
                btrfs_folio_clamp_set_writeback(fs_info, folio, start, len);
        }
        if (page_ops & PAGE_END_WRITEBACK)
                btrfs_folio_clamp_clear_writeback(fs_info, folio, start, len);

        if (folio != locked_folio && (page_ops & PAGE_UNLOCK))
                btrfs_folio_end_lock(fs_info, folio, start, len);
}

static void __process_folios_contig(struct address_space *mapping,
                                    const struct folio *locked_folio, u64 start,
                                    u64 end, unsigned long page_ops)
{
        struct btrfs_fs_info *fs_info = inode_to_fs_info(mapping->host);
        pgoff_t index = start >> PAGE_SHIFT;
        pgoff_t end_index = end >> PAGE_SHIFT;
        struct folio_batch fbatch;
        int i;

        folio_batch_init(&fbatch);
        while (index <= end_index) {
                int found_folios;

                found_folios = filemap_get_folios_contig(mapping, &index,
                                end_index, &fbatch);
                for (i = 0; i < found_folios; i++) {
                        struct folio *folio = fbatch.folios[i];

                        process_one_folio(fs_info, folio, locked_folio,
                                          page_ops, start, end);
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }
}

static noinline void unlock_delalloc_folio(const struct inode *inode,
                                           struct folio *locked_folio,
                                           u64 start, u64 end)
{
        ASSERT(locked_folio);

        __process_folios_contig(inode->i_mapping, locked_folio, start, end,
                                PAGE_UNLOCK);
}

static noinline int lock_delalloc_folios(struct inode *inode,
                                         struct folio *locked_folio,
                                         u64 start, u64 end)
{
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index = start >> PAGE_SHIFT;
        pgoff_t end_index = end >> PAGE_SHIFT;
        u64 processed_end = start;
        struct folio_batch fbatch;

        folio_batch_init(&fbatch);
        while (index <= end_index) {
                unsigned int found_folios, i;

                found_folios = filemap_get_folios_contig(mapping, &index,
                                end_index, &fbatch);
                if (found_folios == 0)
                        goto out;

                for (i = 0; i < found_folios; i++) {
                        struct folio *folio = fbatch.folios[i];
                        u64 range_start;
                        u32 range_len;

                        if (folio == locked_folio)
                                continue;

                        folio_lock(folio);
                        if (!folio_test_dirty(folio) || folio->mapping != mapping) {
                                folio_unlock(folio);
                                goto out;
                        }
                        range_start = max_t(u64, folio_pos(folio), start);
                        range_len = min_t(u64, folio_next_pos(folio), end + 1) - range_start;
                        btrfs_folio_set_lock(fs_info, folio, range_start, range_len);

                        processed_end = range_start + range_len - 1;
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }

        return 0;
out:
        folio_batch_release(&fbatch);
        if (processed_end > start)
                unlock_delalloc_folio(inode, locked_folio, start, processed_end);
        return -EAGAIN;
}

/*
 * Find and lock a contiguous range of bytes in the file marked as delalloc, no
 * more than @max_bytes.
 *
 * @start:      The original start bytenr to search.
 *              Will store the extent range start bytenr.
 * @end:        The original end bytenr of the search range
 *              Will store the extent range end bytenr.
 *
 * Return true if we find a delalloc range which starts inside the original
 * range, and @start/@end will store the delalloc range start/end.
 *
 * Return false if we can't find any delalloc range which starts inside the
 * original range, and @start/@end will be the non-delalloc range start/end.
 */
EXPORT_FOR_TESTS
noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
                                                 struct folio *locked_folio,
                                                 u64 *start, u64 *end)
{
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        const u64 orig_start = *start;
        const u64 orig_end = *end;
        u64 max_bytes = fs_info->max_extent_size;
        u64 delalloc_start;
        u64 delalloc_end;
        bool found;
        struct extent_state *cached_state = NULL;
        int ret;
        int loops = 0;

        /* Caller should pass a valid @end to indicate the search range end */
        ASSERT(orig_end > orig_start);

        /* The range should at least cover part of the folio */
        ASSERT(!(orig_start >= folio_next_pos(locked_folio) ||
                 orig_end <= folio_pos(locked_folio)));
again:
        /* step one, find a bunch of delalloc bytes starting at start */
        delalloc_start = *start;
        delalloc_end = 0;

        /*
         * If @max_bytes is smaller than a block, btrfs_find_delalloc_range() can
         * return early without handling any dirty ranges.
         */
        ASSERT(max_bytes >= fs_info->sectorsize);

        found = btrfs_find_delalloc_range(tree, &delalloc_start, &delalloc_end,
                                          max_bytes, &cached_state);
        if (!found || delalloc_end <= *start || delalloc_start > orig_end) {
                *start = delalloc_start;

                /* @delalloc_end can be -1, never go beyond @orig_end */
                *end = min(delalloc_end, orig_end);
                btrfs_free_extent_state(cached_state);
                return false;
        }

        /*
         * start comes from the offset of locked_folio.  We have to lock
         * folios in order, so we can't process delalloc bytes before
         * locked_folio
         */
        if (delalloc_start < *start)
                delalloc_start = *start;

        /*
         * make sure to limit the number of folios we try to lock down
         */
        if (delalloc_end + 1 - delalloc_start > max_bytes)
                delalloc_end = delalloc_start + max_bytes - 1;

        /* step two, lock all the folios after the folios that has start */
        ret = lock_delalloc_folios(inode, locked_folio, delalloc_start,
                                   delalloc_end);
        ASSERT(!ret || ret == -EAGAIN);
        if (ret == -EAGAIN) {
                /*
                 * Some of the folios are gone, lets avoid looping by
                 * shortening the size of the delalloc range we're searching.
                 */
                btrfs_free_extent_state(cached_state);
                cached_state = NULL;
                if (!loops) {
                        max_bytes = fs_info->sectorsize;
                        loops = 1;
                        goto again;
                } else {
                        return false;
                }
        }

        /* step three, lock the state bits for the whole range */
        btrfs_lock_extent(tree, delalloc_start, delalloc_end, &cached_state);

        /* then test to make sure it is all still delalloc */
        ret = btrfs_test_range_bit(tree, delalloc_start, delalloc_end,
                                   EXTENT_DELALLOC, cached_state);

        btrfs_unlock_extent(tree, delalloc_start, delalloc_end, &cached_state);
        if (!ret) {
                unlock_delalloc_folio(inode, locked_folio, delalloc_start,
                                      delalloc_end);
                cond_resched();
                goto again;
        }
        *start = delalloc_start;
        *end = delalloc_end;

        return found;
}

void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
                                  const struct folio *locked_folio,
                                  struct extent_state **cached,
                                  u32 clear_bits, unsigned long page_ops)
{
        btrfs_clear_extent_bit(&inode->io_tree, start, end, clear_bits, cached);

        __process_folios_contig(inode->vfs_inode.i_mapping, locked_folio, start,
                                end, page_ops);
}

static bool btrfs_verify_folio(struct fsverity_info *vi, struct folio *folio,
                               u64 start, u32 len)
{
        struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);

        if (!vi || btrfs_folio_test_uptodate(fs_info, folio, start, len))
                return true;
        return fsverity_verify_folio(vi, folio);
}

static void end_folio_read(struct fsverity_info *vi, struct folio *folio,
                           bool uptodate, u64 start, u32 len)
{
        struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);

        ASSERT(folio_pos(folio) <= start &&
               start + len <= folio_next_pos(folio));

        if (uptodate && btrfs_verify_folio(vi, folio, start, len))
                btrfs_folio_set_uptodate(fs_info, folio, start, len);
        else
                btrfs_folio_clear_uptodate(fs_info, folio, start, len);

        if (!btrfs_is_subpage(fs_info, folio))
                folio_unlock(folio);
        else
                btrfs_folio_end_lock(fs_info, folio, start, len);
}

/*
 * After a write IO is done, we need to:
 *
 * - clear the uptodate bits on error
 * - clear the writeback bits in the extent tree for the range
 * - filio_end_writeback()  if there is no more pending io for the folio
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bbio_data_write(struct btrfs_bio *bbio)
{
        struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
        struct bio *bio = &bbio->bio;
        int error = blk_status_to_errno(bio->bi_status);
        struct folio_iter fi;
        const u32 sectorsize = fs_info->sectorsize;

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_folio_all(fi, bio) {
                struct folio *folio = fi.folio;
                u64 start = folio_pos(folio) + fi.offset;
                u32 len = fi.length;

                /* Our read/write should always be sector aligned. */
                if (!IS_ALIGNED(fi.offset, sectorsize))
                        btrfs_err(fs_info,
                "partial page write in btrfs with offset %zu and length %zu",
                                  fi.offset, fi.length);
                else if (!IS_ALIGNED(fi.length, sectorsize))
                        btrfs_info(fs_info,
                "incomplete page write with offset %zu and length %zu",
                                   fi.offset, fi.length);

                btrfs_finish_ordered_extent(bbio->ordered, folio, start, len,
                                            !error);
                if (error)
                        mapping_set_error(folio->mapping, error);
                btrfs_folio_clear_writeback(fs_info, folio, start, len);
        }

        bio_put(bio);
}

static void begin_folio_read(struct btrfs_fs_info *fs_info, struct folio *folio)
{
        ASSERT(folio_test_locked(folio));
        if (!btrfs_is_subpage(fs_info, folio))
                return;

        ASSERT(folio_test_private(folio));
        btrfs_folio_set_lock(fs_info, folio, folio_pos(folio), folio_size(folio));
}

/*
 * After a data read IO is done, we need to:
 *
 * - clear the uptodate bits on error
 * - set the uptodate bits if things worked
 * - set the folio up to date if all extents in the tree are uptodate
 * - clear the lock bit in the extent tree
 * - unlock the folio if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bbio_data_read(struct btrfs_bio *bbio)
{
        struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
        struct inode *inode = &bbio->inode->vfs_inode;
        struct bio *bio = &bbio->bio;
        struct fsverity_info *vi = NULL;
        struct folio_iter fi;

        ASSERT(!bio_flagged(bio, BIO_CLONED));

        if (bbio->file_offset < i_size_read(inode))
                vi = fsverity_get_info(inode);

        bio_for_each_folio_all(fi, &bbio->bio) {
                bool uptodate = !bio->bi_status;
                struct folio *folio = fi.folio;
                u64 start = folio_pos(folio) + fi.offset;

                btrfs_debug(fs_info,
                        "%s: bi_sector=%llu, err=%d, mirror=%u",
                        __func__, bio->bi_iter.bi_sector, bio->bi_status,
                        bbio->mirror_num);


                if (likely(uptodate)) {
                        u64 end = start + fi.length - 1;
                        loff_t i_size = i_size_read(inode);

                        /*
                         * Zero out the remaining part if this range straddles
                         * i_size.
                         *
                         * Here we should only zero the range inside the folio,
                         * not touch anything else.
                         *
                         * NOTE: i_size is exclusive while end is inclusive and
                         * folio_contains() takes PAGE_SIZE units.
                         */
                        if (folio_contains(folio, i_size >> PAGE_SHIFT) &&
                            i_size <= end) {
                                u32 zero_start = max(offset_in_folio(folio, i_size),
                                                     offset_in_folio(folio, start));
                                u32 zero_len = offset_in_folio(folio, end) + 1 -
                                               zero_start;

                                folio_zero_range(folio, zero_start, zero_len);
                        }
                }

                /* Update page status and unlock. */
                end_folio_read(vi, folio, uptodate, start, fi.length);
        }
        bio_put(bio);
}

/*
 * Populate every free slot in a provided array with folios using GFP_NOFS.
 *
 * @nr_folios:   number of folios to allocate
 * @order:       the order of the folios to be allocated
 * @folio_array: the array to fill with folios; any existing non-NULL entries in
 *               the array will be skipped
 *
 * Return: 0        if all folios were able to be allocated;
 *         -ENOMEM  otherwise, the partially allocated folios would be freed and
 *                  the array slots zeroed
 */
int btrfs_alloc_folio_array(unsigned int nr_folios, unsigned int order,
                            struct folio **folio_array)
{
        for (int i = 0; i < nr_folios; i++) {
                if (folio_array[i])
                        continue;
                folio_array[i] = folio_alloc(GFP_NOFS, order);
                if (!folio_array[i])
                        goto error;
        }
        return 0;
error:
        for (int i = 0; i < nr_folios; i++) {
                if (folio_array[i])
                        folio_put(folio_array[i]);
                folio_array[i] = NULL;
        }
        return -ENOMEM;
}

/*
 * Populate every free slot in a provided array with pages, using GFP_NOFS.
 *
 * @nr_pages:   number of pages to allocate
 * @page_array: the array to fill with pages; any existing non-null entries in
 *              the array will be skipped
 * @nofail:     whether using __GFP_NOFAIL flag
 *
 * Return: 0        if all pages were able to be allocated;
 *         -ENOMEM  otherwise, the partially allocated pages would be freed and
 *                  the array slots zeroed
 */
int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array,
                           bool nofail)
{
        const gfp_t gfp = nofail ? (GFP_NOFS | __GFP_NOFAIL) : GFP_NOFS;
        unsigned int allocated;

        for (allocated = 0; allocated < nr_pages;) {
                unsigned int last = allocated;

                allocated = alloc_pages_bulk(gfp, nr_pages, page_array);
                if (unlikely(allocated == last)) {
                        /* No progress, fail and do cleanup. */
                        for (int i = 0; i < allocated; i++) {
                                __free_page(page_array[i]);
                                page_array[i] = NULL;
                        }
                        return -ENOMEM;
                }
        }
        return 0;
}

/*
 * Populate needed folios for the extent buffer.
 *
 * For now, the folios populated are always in order 0 (aka, single page).
 */
static int alloc_eb_folio_array(struct extent_buffer *eb, bool nofail)
{
        struct page *page_array[INLINE_EXTENT_BUFFER_PAGES] = { 0 };
        int num_pages = num_extent_pages(eb);
        int ret;

        ret = btrfs_alloc_page_array(num_pages, page_array, nofail);
        if (ret < 0)
                return ret;

        for (int i = 0; i < num_pages; i++)
                eb->folios[i] = page_folio(page_array[i]);
        eb->folio_size = PAGE_SIZE;
        eb->folio_shift = PAGE_SHIFT;
        return 0;
}

static bool btrfs_bio_is_contig(struct btrfs_bio_ctrl *bio_ctrl,
                                u64 disk_bytenr, loff_t file_offset)
{
        struct bio *bio = &bio_ctrl->bbio->bio;
        const sector_t sector = disk_bytenr >> SECTOR_SHIFT;

        if (bio_ctrl->compress_type != BTRFS_COMPRESS_NONE) {
                /*
                 * For compression, all IO should have its logical bytenr set
                 * to the starting bytenr of the compressed extent.
                 */
                return bio->bi_iter.bi_sector == sector;
        }

        /*
         * To merge into a bio both the disk sector and the logical offset in
         * the file need to be contiguous.
         */
        return bio_ctrl->next_file_offset == file_offset &&
                bio_end_sector(bio) == sector;
}

static void alloc_new_bio(struct btrfs_inode *inode,
                          struct btrfs_bio_ctrl *bio_ctrl,
                          u64 disk_bytenr, u64 file_offset)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct btrfs_bio *bbio;

        bbio = btrfs_bio_alloc(BIO_MAX_VECS, bio_ctrl->opf, inode,
                               file_offset, bio_ctrl->end_io_func, NULL);
        bbio->bio.bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
        bbio->bio.bi_write_hint = inode->vfs_inode.i_write_hint;
        bio_ctrl->bbio = bbio;
        bio_ctrl->len_to_oe_boundary = U32_MAX;
        bio_ctrl->next_file_offset = file_offset;

        /* Limit data write bios to the ordered boundary. */
        if (bio_ctrl->wbc) {
                struct btrfs_ordered_extent *ordered;

                ordered = btrfs_lookup_ordered_extent(inode, file_offset);
                if (ordered) {
                        bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
                                        ordered->file_offset +
                                        ordered->disk_num_bytes - file_offset);
                        bbio->ordered = ordered;
                }

                /*
                 * Pick the last added device to support cgroup writeback.  For
                 * multi-device file systems this means blk-cgroup policies have
                 * to always be set on the last added/replaced device.
                 * This is a bit odd but has been like that for a long time.
                 */
                bio_set_dev(&bbio->bio, fs_info->fs_devices->latest_dev->bdev);
                wbc_init_bio(bio_ctrl->wbc, &bbio->bio);
        }
}

/*
 * @disk_bytenr: logical bytenr where the write will be
 * @page:       page to add to the bio
 * @size:       portion of page that we want to write to
 * @pg_offset:  offset of the new bio or to check whether we are adding
 *              a contiguous page to the previous one
 * @read_em_generation: generation of the extent_map we are submitting
 *                      (only used for read)
 *
 * The will either add the page into the existing @bio_ctrl->bbio, or allocate a
 * new one in @bio_ctrl->bbio.
 * The mirror number for this IO should already be initialized in
 * @bio_ctrl->mirror_num.
 */
static void submit_extent_folio(struct btrfs_bio_ctrl *bio_ctrl,
                               u64 disk_bytenr, struct folio *folio,
                               size_t size, unsigned long pg_offset,
                               u64 read_em_generation)
{
        struct btrfs_inode *inode = folio_to_inode(folio);
        loff_t file_offset = folio_pos(folio) + pg_offset;

        ASSERT(pg_offset + size <= folio_size(folio));
        ASSERT(bio_ctrl->end_io_func);

        if (bio_ctrl->bbio &&
            !btrfs_bio_is_contig(bio_ctrl, disk_bytenr, file_offset))
                submit_one_bio(bio_ctrl);

        do {
                u32 len = size;

                /* Allocate new bio if needed */
                if (!bio_ctrl->bbio)
                        alloc_new_bio(inode, bio_ctrl, disk_bytenr, file_offset);

                /* Cap to the current ordered extent boundary if there is one. */
                if (len > bio_ctrl->len_to_oe_boundary) {
                        ASSERT(bio_ctrl->compress_type == BTRFS_COMPRESS_NONE);
                        ASSERT(is_data_inode(inode));
                        len = bio_ctrl->len_to_oe_boundary;
                }

                if (!bio_add_folio(&bio_ctrl->bbio->bio, folio, len, pg_offset)) {
                        /* bio full: move on to a new one */
                        submit_one_bio(bio_ctrl);
                        continue;
                }
                /*
                 * Now that the folio is definitely added to the bio, include its
                 * generation in the max generation calculation.
                 */
                bio_ctrl->generation = max(bio_ctrl->generation, read_em_generation);
                bio_ctrl->next_file_offset += len;

                if (bio_ctrl->wbc)
                        wbc_account_cgroup_owner(bio_ctrl->wbc, folio, len);

                size -= len;
                pg_offset += len;
                disk_bytenr += len;
                file_offset += len;

                /*
                 * len_to_oe_boundary defaults to U32_MAX, which isn't folio or
                 * sector aligned.  alloc_new_bio() then sets it to the end of
                 * our ordered extent for writes into zoned devices.
                 *
                 * When len_to_oe_boundary is tracking an ordered extent, we
                 * trust the ordered extent code to align things properly, and
                 * the check above to cap our write to the ordered extent
                 * boundary is correct.
                 *
                 * When len_to_oe_boundary is U32_MAX, the cap above would
                 * result in a 4095 byte IO for the last folio right before
                 * we hit the bio limit of UINT_MAX.  bio_add_folio() has all
                 * the checks required to make sure we don't overflow the bio,
                 * and we should just ignore len_to_oe_boundary completely
                 * unless we're using it to track an ordered extent.
                 *
                 * It's pretty hard to make a bio sized U32_MAX, but it can
                 * happen when the page cache is able to feed us contiguous
                 * folios for large extents.
                 */
                if (bio_ctrl->len_to_oe_boundary != U32_MAX)
                        bio_ctrl->len_to_oe_boundary -= len;

                /* Ordered extent boundary: move on to a new bio. */
                if (bio_ctrl->len_to_oe_boundary == 0)
                        submit_one_bio(bio_ctrl);
        } while (size);
}

static int attach_extent_buffer_folio(struct extent_buffer *eb,
                                      struct folio *folio,
                                      struct btrfs_folio_state *prealloc)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        int ret = 0;

        /*
         * If the page is mapped to btree inode, we should hold the private
         * lock to prevent race.
         * For cloned or dummy extent buffers, their pages are not mapped and
         * will not race with any other ebs.
         */
        if (folio->mapping)
                lockdep_assert_held(&folio->mapping->i_private_lock);

        if (!btrfs_meta_is_subpage(fs_info)) {
                if (!folio_test_private(folio))
                        folio_attach_private(folio, eb);
                else
                        WARN_ON(folio_get_private(folio) != eb);
                return 0;
        }

        /* Already mapped, just free prealloc */
        if (folio_test_private(folio)) {
                btrfs_free_folio_state(prealloc);
                return 0;
        }

        if (prealloc)
                /* Has preallocated memory for subpage */
                folio_attach_private(folio, prealloc);
        else
                /* Do new allocation to attach subpage */
                ret = btrfs_attach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);
        return ret;
}

int set_folio_extent_mapped(struct folio *folio)
{
        struct btrfs_fs_info *fs_info;

        ASSERT(folio->mapping);

        if (folio_test_private(folio))
                return 0;

        fs_info = folio_to_fs_info(folio);

        if (btrfs_is_subpage(fs_info, folio))
                return btrfs_attach_folio_state(fs_info, folio, BTRFS_SUBPAGE_DATA);

        folio_attach_private(folio, (void *)EXTENT_FOLIO_PRIVATE);
        return 0;
}

void clear_folio_extent_mapped(struct folio *folio)
{
        struct btrfs_fs_info *fs_info;

        ASSERT(folio->mapping);

        if (!folio_test_private(folio))
                return;

        fs_info = folio_to_fs_info(folio);
        if (btrfs_is_subpage(fs_info, folio))
                return btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_DATA);

        folio_detach_private(folio);
}

static struct extent_map *get_extent_map(struct btrfs_inode *inode,
                                         struct folio *folio, u64 start,
                                         u64 len, struct extent_map **em_cached)
{
        struct extent_map *em;

        ASSERT(em_cached);

        if (*em_cached) {
                em = *em_cached;
                if (btrfs_extent_map_in_tree(em) && start >= em->start &&
                    start < btrfs_extent_map_end(em)) {
                        refcount_inc(&em->refs);
                        return em;
                }

                btrfs_free_extent_map(em);
                *em_cached = NULL;
        }

        em = btrfs_get_extent(inode, folio, start, len);
        if (!IS_ERR(em)) {
                BUG_ON(*em_cached);
                refcount_inc(&em->refs);
                *em_cached = em;
        }

        return em;
}

static void btrfs_readahead_expand(struct readahead_control *ractl,
                                   const struct extent_map *em)
{
        const u64 ra_pos = readahead_pos(ractl);
        const u64 ra_end = ra_pos + readahead_length(ractl);
        const u64 em_end = btrfs_extent_map_end(em);

        /* No expansion for holes and inline extents. */
        if (em->disk_bytenr > EXTENT_MAP_LAST_BYTE)
                return;

        ASSERT(em_end >= ra_pos,
               "extent_map %llu %llu ends before current readahead position %llu",
               em->start, em->len, ra_pos);
        if (em_end > ra_end)
                readahead_expand(ractl, ra_pos, em_end - ra_pos);
}

/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 * XXX JDM: This needs looking at to ensure proper page locking
 * return 0 on success, otherwise return error
 */
static int btrfs_do_readpage(struct folio *folio, struct extent_map **em_cached,
                             struct btrfs_bio_ctrl *bio_ctrl,
                             struct fsverity_info *vi)
{
        struct inode *inode = folio->mapping->host;
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        u64 start = folio_pos(folio);
        const u64 end = start + folio_size(folio) - 1;
        u64 extent_offset;
        u64 locked_end;
        u64 last_byte = i_size_read(inode);
        struct extent_map *em;
        int ret = 0;
        const size_t blocksize = fs_info->sectorsize;

        if (bio_ctrl->ractl)
                locked_end = readahead_pos(bio_ctrl->ractl) + readahead_length(bio_ctrl->ractl) - 1;
        else
                locked_end = end;

        ret = set_folio_extent_mapped(folio);
        if (ret < 0) {
                folio_unlock(folio);
                return ret;
        }

        if (folio_contains(folio, last_byte >> PAGE_SHIFT)) {
                size_t zero_offset = offset_in_folio(folio, last_byte);

                if (zero_offset)
                        folio_zero_range(folio, zero_offset,
                                         folio_size(folio) - zero_offset);
        }
        bio_ctrl->end_io_func = end_bbio_data_read;
        begin_folio_read(fs_info, folio);
        for (u64 cur = start; cur <= end; cur += blocksize) {
                enum btrfs_compression_type compress_type = BTRFS_COMPRESS_NONE;
                unsigned long pg_offset = offset_in_folio(folio, cur);
                bool force_bio_submit = false;
                u64 disk_bytenr;
                u64 block_start;
                u64 em_gen;

                ASSERT(IS_ALIGNED(cur, fs_info->sectorsize));
                if (cur >= last_byte) {
                        folio_zero_range(folio, pg_offset, end - cur + 1);
                        end_folio_read(vi, folio, true, cur, end - cur + 1);
                        break;
                }
                if (btrfs_folio_test_uptodate(fs_info, folio, cur, blocksize)) {
                        end_folio_read(vi, folio, true, cur, blocksize);
                        continue;
                }
                /*
                 * Search extent map for the whole locked range.
                 * This will allow btrfs_get_extent() to return a larger hole
                 * when possible.
                 * This can reduce duplicated btrfs_get_extent() calls for large
                 * holes.
                 */
                em = get_extent_map(BTRFS_I(inode), folio, cur, locked_end - cur + 1, em_cached);
                if (IS_ERR(em)) {
                        end_folio_read(vi, folio, false, cur, end + 1 - cur);
                        return PTR_ERR(em);
                }
                extent_offset = cur - em->start;
                BUG_ON(btrfs_extent_map_end(em) <= cur);
                BUG_ON(end < cur);

                compress_type = btrfs_extent_map_compression(em);

                /*
                 * Only expand readahead for extents which are already creating
                 * the pages anyway in add_ra_bio_pages, which is compressed
                 * extents in the non subpage case.
                 */
                if (bio_ctrl->ractl &&
                    !btrfs_is_subpage(fs_info, folio) &&
                    compress_type != BTRFS_COMPRESS_NONE)
                        btrfs_readahead_expand(bio_ctrl->ractl, em);

                if (compress_type != BTRFS_COMPRESS_NONE)
                        disk_bytenr = em->disk_bytenr;
                else
                        disk_bytenr = btrfs_extent_map_block_start(em) + extent_offset;

                if (em->flags & EXTENT_FLAG_PREALLOC)
                        block_start = EXTENT_MAP_HOLE;
                else
                        block_start = btrfs_extent_map_block_start(em);

                /*
                 * If we have a file range that points to a compressed extent
                 * and it's followed by a consecutive file range that points
                 * to the same compressed extent (possibly with a different
                 * offset and/or length, so it either points to the whole extent
                 * or only part of it), we must make sure we do not submit a
                 * single bio to populate the folios for the 2 ranges because
                 * this makes the compressed extent read zero out the folios
                 * belonging to the 2nd range. Imagine the following scenario:
                 *
                 *  File layout
                 *  [0 - 8K]                     [8K - 24K]
                 *    |                               |
                 *    |                               |
                 * points to extent X,         points to extent X,
                 * offset 4K, length of 8K     offset 0, length 16K
                 *
                 * [extent X, compressed length = 4K uncompressed length = 16K]
                 *
                 * If the bio to read the compressed extent covers both ranges,
                 * it will decompress extent X into the folios belonging to the
                 * first range and then it will stop, zeroing out the remaining
                 * folios that belong to the other range that points to extent X.
                 * So here we make sure we submit 2 bios, one for the first
                 * range and another one for the third range. Both will target
                 * the same physical extent from disk, but we can't currently
                 * make the compressed bio endio callback populate the folios
                 * for both ranges because each compressed bio is tightly
                 * coupled with a single extent map, and each range can have
                 * an extent map with a different offset value relative to the
                 * uncompressed data of our extent and different lengths. This
                 * is a corner case so we prioritize correctness over
                 * non-optimal behavior (submitting 2 bios for the same extent).
                 */
                if (compress_type != BTRFS_COMPRESS_NONE &&
                    bio_ctrl->last_em_start != U64_MAX &&
                    bio_ctrl->last_em_start != em->start)
                        force_bio_submit = true;

                bio_ctrl->last_em_start = em->start;

                em_gen = em->generation;
                btrfs_free_extent_map(em);
                em = NULL;

                /* we've found a hole, just zero and go on */
                if (block_start == EXTENT_MAP_HOLE) {
                        folio_zero_range(folio, pg_offset, blocksize);
                        end_folio_read(vi, folio, true, cur, blocksize);
                        continue;
                }
                /* the get_extent function already copied into the folio */
                if (block_start == EXTENT_MAP_INLINE) {
                        end_folio_read(vi, folio, true, cur, blocksize);
                        continue;
                }

                if (bio_ctrl->compress_type != compress_type) {
                        submit_one_bio(bio_ctrl);
                        bio_ctrl->compress_type = compress_type;
                }

                if (force_bio_submit)
                        submit_one_bio(bio_ctrl);
                submit_extent_folio(bio_ctrl, disk_bytenr, folio, blocksize,
                                    pg_offset, em_gen);
        }
        return 0;
}

/*
 * Check if we can skip waiting the @ordered extent covering the block at @fileoff.
 *
 * @fileoff:    Both input and output.
 *              Input as the file offset where the check should start at.
 *              Output as where the next check should start at,
 *              if the function returns true.
 *
 * Return true if we can skip to @fileoff. The caller needs to check the new
 * @fileoff value to make sure it covers the full range, before skipping the
 * full OE.
 *
 * Return false if we must wait for the ordered extent.
 */
static bool can_skip_one_ordered_range(struct btrfs_inode *inode,
                                       struct btrfs_ordered_extent *ordered,
                                       u64 *fileoff)
{
        const struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct folio *folio;
        const u32 blocksize = fs_info->sectorsize;
        u64 cur = *fileoff;
        bool ret;

        folio = filemap_get_folio(inode->vfs_inode.i_mapping, cur >> PAGE_SHIFT);

        /*
         * We should have locked the folio(s) for range [start, end], thus
         * there must be a folio and it must be locked.
         */
        ASSERT(!IS_ERR(folio));
        ASSERT(folio_test_locked(folio));

        /*
         * There are several cases for the folio and OE combination:
         *
         * 1) Folio has no private flag
         *    The OE has all its IO done but not yet finished, and folio got
         *    invalidated.
         *
         * Have we have to wait for the OE to finish, as it may contain the
         * to-be-inserted data checksum.
         * Without the data checksum inserted into the csum tree, read will
         * just fail with missing csum.
         */
        if (!folio_test_private(folio)) {
                ret = false;
                goto out;
        }

        /*
         * 2) The first block is DIRTY.
         *
         * This means the OE is created by some other folios whose file pos is
         * before this one. And since we are holding the folio lock, the writeback
         * of this folio cannot start.
         *
         * We must skip the whole OE, because it will never start until we
         * finished our folio read and unlocked the folio.
         */
        if (btrfs_folio_test_dirty(fs_info, folio, cur, blocksize)) {
                u64 range_len = umin(folio_next_pos(folio),
                                    ordered->file_offset + ordered->num_bytes) - cur;

                ret = true;
                /*
                 * At least inside the folio, all the remaining blocks should
                 * also be dirty.
                 */
                ASSERT(btrfs_folio_test_dirty(fs_info, folio, cur, range_len));
                *fileoff = ordered->file_offset + ordered->num_bytes;
                goto out;
        }

        /*
         * 3) The first block is uptodate.
         *
         * At least the first block can be skipped, but we are still not fully
         * sure. E.g. if the OE has some other folios in the range that cannot
         * be skipped.
         * So we return true and update @next_ret to the OE/folio boundary.
         */
        if (btrfs_folio_test_uptodate(fs_info, folio, cur, blocksize)) {
                u64 range_len = umin(folio_next_pos(folio),
                                    ordered->file_offset + ordered->num_bytes) - cur;

                /*
                 * The whole range to the OE end or folio boundary should also
                 * be uptodate.
                 */
                ASSERT(btrfs_folio_test_uptodate(fs_info, folio, cur, range_len));
                ret = true;
                *fileoff = cur + range_len;
                goto out;
        }

        /*
         * 4) The first block is not uptodate.
         *
         * This means the folio is invalidated after the writeback was finished,
         * but by some other operations (e.g. block aligned buffered write) the
         * folio is inserted into filemap.
         * Very much the same as case 1).
         */
        ret = false;
out:
        folio_put(folio);
        return ret;
}

static bool can_skip_ordered_extent(struct btrfs_inode *inode,
                                    struct btrfs_ordered_extent *ordered,
                                    u64 start, u64 end)
{
        const u64 range_end = min(end, ordered->file_offset + ordered->num_bytes - 1);
        u64 cur = max(start, ordered->file_offset);

        while (cur < range_end) {
                bool can_skip;

                can_skip = can_skip_one_ordered_range(inode, ordered, &cur);
                if (!can_skip)
                        return false;
        }
        return true;
}

/*
 * Locking helper to make sure we get a stable view of extent maps for the
 * involved range.
 *
 * This is for folio read paths (read and readahead), thus the involved range
 * should have all the folios locked.
 */
static void lock_extents_for_read(struct btrfs_inode *inode, u64 start, u64 end,
                                  struct extent_state **cached_state)
{
        u64 cur_pos;

        /* Caller must provide a valid @cached_state. */
        ASSERT(cached_state);

        /* The range must at least be page aligned, as all read paths are folio based. */
        ASSERT(IS_ALIGNED(start, PAGE_SIZE));
        ASSERT(IS_ALIGNED(end + 1, PAGE_SIZE));

again:
        btrfs_lock_extent(&inode->io_tree, start, end, cached_state);
        cur_pos = start;
        while (cur_pos < end) {
                struct btrfs_ordered_extent *ordered;

                ordered = btrfs_lookup_ordered_range(inode, cur_pos,
                                                     end - cur_pos + 1);
                /*
                 * No ordered extents in the range, and we hold the extent lock,
                 * no one can modify the extent maps in the range, we're safe to return.
                 */
                if (!ordered)
                        break;

                /* Check if we can skip waiting for the whole OE. */
                if (can_skip_ordered_extent(inode, ordered, start, end)) {
                        cur_pos = min(ordered->file_offset + ordered->num_bytes,
                                      end + 1);
                        btrfs_put_ordered_extent(ordered);
                        continue;
                }

                /* Now wait for the OE to finish. */
                btrfs_unlock_extent(&inode->io_tree, start, end, cached_state);
                btrfs_start_ordered_extent_nowriteback(ordered, start, end + 1 - start);
                btrfs_put_ordered_extent(ordered);
                /* We have unlocked the whole range, restart from the beginning. */
                goto again;
        }
}

int btrfs_read_folio(struct file *file, struct folio *folio)
{
        struct inode *vfs_inode = folio->mapping->host;
        struct btrfs_inode *inode = BTRFS_I(vfs_inode);
        const u64 start = folio_pos(folio);
        const u64 end = start + folio_size(folio) - 1;
        struct extent_state *cached_state = NULL;
        struct btrfs_bio_ctrl bio_ctrl = {
                .opf = REQ_OP_READ,
                .last_em_start = U64_MAX,
        };
        struct extent_map *em_cached = NULL;
        struct fsverity_info *vi = NULL;
        int ret;

        lock_extents_for_read(inode, start, end, &cached_state);
        if (folio_pos(folio) < i_size_read(vfs_inode))
                vi = fsverity_get_info(vfs_inode);
        ret = btrfs_do_readpage(folio, &em_cached, &bio_ctrl, vi);
        btrfs_unlock_extent(&inode->io_tree, start, end, &cached_state);

        btrfs_free_extent_map(em_cached);

        /*
         * If btrfs_do_readpage() failed we will want to submit the assembled
         * bio to do the cleanup.
         */
        submit_one_bio(&bio_ctrl);
        return ret;
}

static void set_delalloc_bitmap(struct folio *folio, unsigned long *delalloc_bitmap,
                                u64 start, u32 len)
{
        struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
        const u64 folio_start = folio_pos(folio);
        unsigned int start_bit;
        unsigned int nbits;

        ASSERT(start >= folio_start && start + len <= folio_start + folio_size(folio));
        start_bit = (start - folio_start) >> fs_info->sectorsize_bits;
        nbits = len >> fs_info->sectorsize_bits;
        ASSERT(bitmap_test_range_all_zero(delalloc_bitmap, start_bit, nbits));
        bitmap_set(delalloc_bitmap, start_bit, nbits);
}

static bool find_next_delalloc_bitmap(struct folio *folio,
                                      unsigned long *delalloc_bitmap, u64 start,
                                      u64 *found_start, u32 *found_len)
{
        struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
        const u64 folio_start = folio_pos(folio);
        const unsigned int bitmap_size = btrfs_blocks_per_folio(fs_info, folio);
        unsigned int start_bit;
        unsigned int first_zero;
        unsigned int first_set;

        ASSERT(start >= folio_start && start < folio_start + folio_size(folio));

        start_bit = (start - folio_start) >> fs_info->sectorsize_bits;
        first_set = find_next_bit(delalloc_bitmap, bitmap_size, start_bit);
        if (first_set >= bitmap_size)
                return false;

        *found_start = folio_start + (first_set << fs_info->sectorsize_bits);
        first_zero = find_next_zero_bit(delalloc_bitmap, bitmap_size, first_set);
        *found_len = (first_zero - first_set) << fs_info->sectorsize_bits;
        return true;
}

/*
 * Do all of the delayed allocation setup.
 *
 * Return >0 if all the dirty blocks are submitted async (compression) or inlined.
 * The @folio should no longer be touched (treat it as already unlocked).
 *
 * Return 0 if there is still dirty block that needs to be submitted through
 * extent_writepage_io().
 * bio_ctrl->submit_bitmap will indicate which blocks of the folio should be
 * submitted, and @folio is still kept locked.
 *
 * Return <0 if there is any error hit.
 * Any allocated ordered extent range covering this folio will be marked
 * finished (IOERR), and @folio is still kept locked.
 */
static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
                                                 struct folio *folio,
                                                 struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_fs_info *fs_info = inode_to_fs_info(&inode->vfs_inode);
        struct writeback_control *wbc = bio_ctrl->wbc;
        const bool is_subpage = btrfs_is_subpage(fs_info, folio);
        const u64 page_start = folio_pos(folio);
        const u64 page_end = page_start + folio_size(folio) - 1;
        const unsigned int blocks_per_folio = btrfs_blocks_per_folio(fs_info, folio);
        unsigned long delalloc_bitmap = 0;
        /*
         * Save the last found delalloc end. As the delalloc end can go beyond
         * page boundary, thus we cannot rely on subpage bitmap to locate the
         * last delalloc end.
         */
        u64 last_delalloc_end = 0;
        /*
         * The range end (exclusive) of the last successfully finished delalloc
         * range.
         * Any range covered by ordered extent must either be manually marked
         * finished (error handling), or has IO submitted (and finish the
         * ordered extent normally).
         *
         * This records the end of ordered extent cleanup if we hit an error.
         */
        u64 last_finished_delalloc_end = page_start;
        u64 delalloc_start = page_start;
        u64 delalloc_end = page_end;
        u64 delalloc_to_write = 0;
        unsigned int start_bit;
        unsigned int end_bit;
        int ret = 0;

        /* Save the dirty bitmap as our submission bitmap will be a subset of it. */
        if (btrfs_is_subpage(fs_info, folio)) {
                ASSERT(blocks_per_folio > 1);
                btrfs_get_subpage_dirty_bitmap(fs_info, folio, &bio_ctrl->submit_bitmap);
        } else {
                bio_ctrl->submit_bitmap = 1;
        }

        for_each_set_bitrange(start_bit, end_bit, &bio_ctrl->submit_bitmap,
                              blocks_per_folio) {
                u64 start = page_start + (start_bit << fs_info->sectorsize_bits);
                u32 len = (end_bit - start_bit) << fs_info->sectorsize_bits;

                btrfs_folio_set_lock(fs_info, folio, start, len);
        }

        /* Lock all (subpage) delalloc ranges inside the folio first. */
        while (delalloc_start < page_end) {
                delalloc_end = page_end;
                if (!find_lock_delalloc_range(&inode->vfs_inode, folio,
                                              &delalloc_start, &delalloc_end)) {
                        delalloc_start = delalloc_end + 1;
                        continue;
                }
                set_delalloc_bitmap(folio, &delalloc_bitmap, delalloc_start,
                                    min(delalloc_end, page_end) + 1 - delalloc_start);
                last_delalloc_end = delalloc_end;
                delalloc_start = delalloc_end + 1;
        }
        delalloc_start = page_start;

        if (!last_delalloc_end)
                goto out;

        /* Run the delalloc ranges for the above locked ranges. */
        while (delalloc_start < page_end) {
                u64 found_start;
                u32 found_len;
                bool found;

                if (!is_subpage) {
                        /*
                         * For non-subpage case, the found delalloc range must
                         * cover this folio and there must be only one locked
                         * delalloc range.
                         */
                        found_start = page_start;
                        found_len = last_delalloc_end + 1 - found_start;
                        found = true;
                } else {
                        found = find_next_delalloc_bitmap(folio, &delalloc_bitmap,
                                        delalloc_start, &found_start, &found_len);
                }
                if (!found)
                        break;
                /*
                 * The subpage range covers the last sector, the delalloc range may
                 * end beyond the folio boundary, use the saved delalloc_end
                 * instead.
                 */
                if (found_start + found_len >= page_end)
                        found_len = last_delalloc_end + 1 - found_start;

                if (ret >= 0) {
                        /*
                         * Some delalloc range may be created by previous folios.
                         * Thus we still need to clean up this range during error
                         * handling.
                         */
                        last_finished_delalloc_end = found_start;
                        /* No errors hit so far, run the current delalloc range. */
                        ret = btrfs_run_delalloc_range(inode, folio,
                                                       found_start,
                                                       found_start + found_len - 1,
                                                       wbc);
                        if (ret >= 0)
                                last_finished_delalloc_end = found_start + found_len;
                        if (unlikely(ret < 0))
                                btrfs_err_rl(fs_info,
"failed to run delalloc range, root=%lld ino=%llu folio=%llu submit_bitmap=%*pbl start=%llu len=%u: %d",
                                             btrfs_root_id(inode->root),
                                             btrfs_ino(inode),
                                             folio_pos(folio),
                                             blocks_per_folio,
                                             &bio_ctrl->submit_bitmap,
                                             found_start, found_len, ret);
                } else {
                        /*
                         * We've hit an error during previous delalloc range,
                         * have to cleanup the remaining locked ranges.
                         */
                        btrfs_unlock_extent(&inode->io_tree, found_start,
                                            found_start + found_len - 1, NULL);
                        unlock_delalloc_folio(&inode->vfs_inode, folio,
                                              found_start,
                                              found_start + found_len - 1);
                }

                /*
                 * We have some ranges that's going to be submitted asynchronously
                 * (compression or inline).  These range have their own control
                 * on when to unlock the pages.  We should not touch them
                 * anymore, so clear the range from the submission bitmap.
                 */
                if (ret > 0) {
                        unsigned int start_bit = (found_start - page_start) >>
                                                 fs_info->sectorsize_bits;
                        unsigned int end_bit = (min(page_end + 1, found_start + found_len) -
                                                page_start) >> fs_info->sectorsize_bits;
                        bitmap_clear(&bio_ctrl->submit_bitmap, start_bit, end_bit - start_bit);
                }
                /*
                 * Above btrfs_run_delalloc_range() may have unlocked the folio,
                 * thus for the last range, we cannot touch the folio anymore.
                 */
                if (found_start + found_len >= last_delalloc_end + 1)
                        break;

                delalloc_start = found_start + found_len;
        }
        /*
         * It's possible we had some ordered extents created before we hit
         * an error, cleanup non-async successfully created delalloc ranges.
         */
        if (unlikely(ret < 0)) {
                unsigned int bitmap_size = min(
                                (last_finished_delalloc_end - page_start) >>
                                fs_info->sectorsize_bits,
                                blocks_per_folio);

                for_each_set_bitrange(start_bit, end_bit, &bio_ctrl->submit_bitmap,
                                      bitmap_size) {
                        u64 start = page_start + (start_bit << fs_info->sectorsize_bits);
                        u32 len = (end_bit - start_bit) << fs_info->sectorsize_bits;

                        btrfs_mark_ordered_io_finished(inode, folio, start, len, false);
                }
                return ret;
        }
out:
        if (last_delalloc_end)
                delalloc_end = last_delalloc_end;
        else
                delalloc_end = page_end;
        /*
         * delalloc_end is already one less than the total length, so
         * we don't subtract one from PAGE_SIZE.
         */
        delalloc_to_write +=
                DIV_ROUND_UP(delalloc_end + 1 - page_start, PAGE_SIZE);

        /*
         * If all ranges are submitted asynchronously, we just need to account
         * for them here.
         */
        if (bitmap_empty(&bio_ctrl->submit_bitmap, blocks_per_folio)) {
                wbc->nr_to_write -= delalloc_to_write;
                return 1;
        }

        if (wbc->nr_to_write < delalloc_to_write) {
                int thresh = 8192;

                if (delalloc_to_write < thresh * 2)
                        thresh = delalloc_to_write;
                wbc->nr_to_write = min_t(u64, delalloc_to_write,
                                         thresh);
        }

        return 0;
}

/*
 * Return 0 if we have submitted or queued the sector for submission.
 * Return <0 for critical errors, and the involved sector will be cleaned up.
 *
 * Caller should make sure filepos < i_size and handle filepos >= i_size case.
 */
static int submit_one_sector(struct btrfs_inode *inode,
                             struct folio *folio,
                             u64 filepos, struct btrfs_bio_ctrl *bio_ctrl,
                             loff_t i_size)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map *em;
        u64 block_start;
        u64 disk_bytenr;
        u64 extent_offset;
        u64 em_end;
        const u32 sectorsize = fs_info->sectorsize;

        ASSERT(IS_ALIGNED(filepos, sectorsize));

        /* @filepos >= i_size case should be handled by the caller. */
        ASSERT(filepos < i_size);

        em = btrfs_get_extent(inode, NULL, filepos, sectorsize);
        if (IS_ERR(em)) {
                /*
                 * bio_ctrl may contain a bio crossing several folios.
                 * Submit it immediately so that the bio has a chance
                 * to finish normally, other than marked as error.
                 */
                submit_one_bio(bio_ctrl);

                /*
                 * When submission failed, we should still clear the folio dirty.
                 * Or the folio will be written back again but without any
                 * ordered extent.
                 */
                btrfs_folio_clear_dirty(fs_info, folio, filepos, sectorsize);
                btrfs_folio_set_writeback(fs_info, folio, filepos, sectorsize);
                btrfs_folio_clear_writeback(fs_info, folio, filepos, sectorsize);

                /*
                 * Since there is no bio submitted to finish the ordered
                 * extent, we have to manually finish this sector.
                 */
                btrfs_mark_ordered_io_finished(inode, folio, filepos,
                                               fs_info->sectorsize, false);
                return PTR_ERR(em);
        }

        extent_offset = filepos - em->start;
        em_end = btrfs_extent_map_end(em);
        ASSERT(filepos <= em_end);
        ASSERT(IS_ALIGNED(em->start, sectorsize));
        ASSERT(IS_ALIGNED(em->len, sectorsize));

        block_start = btrfs_extent_map_block_start(em);
        disk_bytenr = btrfs_extent_map_block_start(em) + extent_offset;

        ASSERT(!btrfs_extent_map_is_compressed(em));
        ASSERT(block_start != EXTENT_MAP_HOLE);
        ASSERT(block_start != EXTENT_MAP_INLINE);

        btrfs_free_extent_map(em);
        em = NULL;

        /*
         * Although the PageDirty bit is cleared before entering this
         * function, subpage dirty bit is not cleared.
         * So clear subpage dirty bit here so next time we won't submit
         * a folio for a range already written to disk.
         */
        btrfs_folio_clear_dirty(fs_info, folio, filepos, sectorsize);
        btrfs_folio_set_writeback(fs_info, folio, filepos, sectorsize);
        /*
         * Above call should set the whole folio with writeback flag, even
         * just for a single subpage sector.
         * As long as the folio is properly locked and the range is correct,
         * we should always get the folio with writeback flag.
         */
        ASSERT(folio_test_writeback(folio));

        submit_extent_folio(bio_ctrl, disk_bytenr, folio,
                            sectorsize, filepos - folio_pos(folio), 0);
        return 0;
}

/*
 * Helper for extent_writepage().  This calls the writepage start hooks,
 * and does the loop to map the page into extents and bios.
 *
 * We return 1 if the IO is started and the page is unlocked,
 * 0 if all went well (page still locked)
 * < 0 if there were errors (page still locked)
 */
static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
                                                  struct folio *folio,
                                                  u64 start, u32 len,
                                                  struct btrfs_bio_ctrl *bio_ctrl,
                                                  loff_t i_size)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        unsigned long range_bitmap = 0;
        bool submitted_io = false;
        int found_error = 0;
        const u64 end = start + len;
        const u64 folio_start = folio_pos(folio);
        const u64 folio_end = folio_start + folio_size(folio);
        const unsigned int blocks_per_folio = btrfs_blocks_per_folio(fs_info, folio);
        u64 cur;
        int bit;
        int ret = 0;

        ASSERT(start >= folio_start, "start=%llu folio_start=%llu", start, folio_start);
        ASSERT(end <= folio_end, "start=%llu len=%u folio_start=%llu folio_size=%zu",
               start, len, folio_start, folio_size(folio));

        ret = btrfs_writepage_cow_fixup(folio);
        if (ret == -EAGAIN) {
                /* Fixup worker will requeue */
                folio_redirty_for_writepage(bio_ctrl->wbc, folio);
                folio_unlock(folio);
                return 1;
        }
        if (ret < 0) {
                btrfs_folio_clear_dirty(fs_info, folio, start, len);
                btrfs_folio_set_writeback(fs_info, folio, start, len);
                btrfs_folio_clear_writeback(fs_info, folio, start, len);
                return ret;
        }

        bitmap_set(&range_bitmap, (start - folio_pos(folio)) >> fs_info->sectorsize_bits,
                   len >> fs_info->sectorsize_bits);
        bitmap_and(&bio_ctrl->submit_bitmap, &bio_ctrl->submit_bitmap, &range_bitmap,
                   blocks_per_folio);

        bio_ctrl->end_io_func = end_bbio_data_write;

        for_each_set_bit(bit, &bio_ctrl->submit_bitmap, blocks_per_folio) {
                cur = folio_pos(folio) + (bit << fs_info->sectorsize_bits);

                if (cur >= i_size) {
                        struct btrfs_ordered_extent *ordered;

                        ordered = btrfs_lookup_first_ordered_range(inode, cur,
                                                                   fs_info->sectorsize);
                        /*
                         * We have just run delalloc before getting here, so
                         * there must be an ordered extent.
                         */
                        ASSERT(ordered != NULL);
                        spin_lock(&inode->ordered_tree_lock);
                        set_bit(BTRFS_ORDERED_TRUNCATED, &ordered->flags);
                        ordered->truncated_len = min(ordered->truncated_len,
                                                     cur - ordered->file_offset);
                        spin_unlock(&inode->ordered_tree_lock);
                        btrfs_put_ordered_extent(ordered);

                        btrfs_mark_ordered_io_finished(inode, folio, cur,
                                                       fs_info->sectorsize, true);
                        /*
                         * This range is beyond i_size, thus we don't need to
                         * bother writing back.
                         * But we still need to clear the dirty subpage bit, or
                         * the next time the folio gets dirtied, we will try to
                         * writeback the sectors with subpage dirty bits,
                         * causing writeback without ordered extent.
                         */
                        btrfs_folio_clear_dirty(fs_info, folio, cur, fs_info->sectorsize);
                        continue;
                }
                ret = submit_one_sector(inode, folio, cur, bio_ctrl, i_size);
                if (unlikely(ret < 0)) {
                        if (!found_error)
                                found_error = ret;
                        continue;
                }
                submitted_io = true;
        }

        /*
         * If we didn't submitted any sector (>= i_size), folio dirty get
         * cleared but PAGECACHE_TAG_DIRTY is not cleared (only cleared
         * by folio_start_writeback() if the folio is not dirty).
         *
         * Here we set writeback and clear for the range. If the full folio
         * is no longer dirty then we clear the PAGECACHE_TAG_DIRTY tag.
         *
         * If we hit any error, the corresponding sector will have its dirty
         * flag cleared and writeback finished, thus no need to handle the error case.
         */
        if (!submitted_io && !found_error) {
                btrfs_folio_set_writeback(fs_info, folio, start, len);
                btrfs_folio_clear_writeback(fs_info, folio, start, len);
        }
        return found_error;
}

/*
 * the writepage semantics are similar to regular writepage.  extent
 * records are inserted to lock ranges in the tree, and as dirty areas
 * are found, they are marked writeback.  Then the lock bits are removed
 * and the end_io handler clears the writeback ranges
 *
 * Return 0 if everything goes well.
 * Return <0 for error.
 */
static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_inode *inode = BTRFS_I(folio->mapping->host);
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        int ret;
        size_t pg_offset;
        loff_t i_size = i_size_read(&inode->vfs_inode);
        const pgoff_t end_index = i_size >> PAGE_SHIFT;
        const unsigned int blocks_per_folio = btrfs_blocks_per_folio(fs_info, folio);

        trace_extent_writepage(folio, &inode->vfs_inode, bio_ctrl->wbc);

        WARN_ON(!folio_test_locked(folio));

        pg_offset = offset_in_folio(folio, i_size);
        if (folio->index > end_index ||
           (folio->index == end_index && !pg_offset)) {
                folio_invalidate(folio, 0, folio_size(folio));
                folio_unlock(folio);
                return 0;
        }

        if (folio_contains(folio, end_index))
                folio_zero_range(folio, pg_offset, folio_size(folio) - pg_offset);

        /*
         * Default to unlock the whole folio.
         * The proper bitmap can only be initialized until writepage_delalloc().
         */
        bio_ctrl->submit_bitmap = (unsigned long)-1;

        /*
         * If the page is dirty but without private set, it's marked dirty
         * without informing the fs.
         * Nowadays that is a bug, since the introduction of
         * pin_user_pages*().
         *
         * So here we check if the page has private set to rule out such
         * case.
         * But we also have a long history of relying on the COW fixup,
         * so here we only enable this check for experimental builds until
         * we're sure it's safe.
         */
        if (IS_ENABLED(CONFIG_BTRFS_EXPERIMENTAL) &&
            unlikely(!folio_test_private(folio))) {
                WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
                btrfs_err_rl(fs_info,
        "root %lld ino %llu folio %llu is marked dirty without notifying the fs",
                             btrfs_root_id(inode->root),
                             btrfs_ino(inode), folio_pos(folio));
                ret = -EUCLEAN;
                goto done;
        }

        ret = set_folio_extent_mapped(folio);
        if (ret < 0)
                goto done;

        ret = writepage_delalloc(inode, folio, bio_ctrl);
        if (ret == 1)
                return 0;
        if (ret)
                goto done;

        ret = extent_writepage_io(inode, folio, folio_pos(folio),
                                  folio_size(folio), bio_ctrl, i_size);
        if (ret == 1)
                return 0;
        if (unlikely(ret < 0))
                btrfs_err_rl(fs_info,
"failed to submit blocks, root=%lld inode=%llu folio=%llu submit_bitmap=%*pbl: %d",
                             btrfs_root_id(inode->root), btrfs_ino(inode),
                             folio_pos(folio), blocks_per_folio,
                             &bio_ctrl->submit_bitmap, ret);

        bio_ctrl->wbc->nr_to_write--;

done:
        if (ret < 0)
                mapping_set_error(folio->mapping, ret);
        /*
         * Only unlock ranges that are submitted. As there can be some async
         * submitted ranges inside the folio.
         */
        btrfs_folio_end_lock_bitmap(fs_info, folio, bio_ctrl->submit_bitmap);
        ASSERT(ret <= 0);
        return ret;
}

/*
 * Lock extent buffer status and pages for writeback.
 *
 * Return %false if the extent buffer doesn't need to be submitted (e.g. the
 * extent buffer is not dirty)
 * Return %true is the extent buffer is submitted to bio.
 */
static noinline_for_stack bool lock_extent_buffer_for_io(struct extent_buffer *eb,
                          struct writeback_control *wbc)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        bool ret = false;

        btrfs_tree_lock(eb);
        while (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
                btrfs_tree_unlock(eb);
                if (wbc->sync_mode != WB_SYNC_ALL)
                        return false;
                wait_on_extent_buffer_writeback(eb);
                btrfs_tree_lock(eb);
        }

        /*
         * We need to do this to prevent races in people who check if the eb is
         * under IO since we can end up having no IO bits set for a short period
         * of time.
         */
        spin_lock(&eb->refs_lock);
        if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                XA_STATE(xas, &fs_info->buffer_tree, eb->start >> fs_info->nodesize_bits);
                unsigned long flags;

                set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
                spin_unlock(&eb->refs_lock);

                xas_lock_irqsave(&xas, flags);
                xas_load(&xas);
                xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
                xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
                xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
                xas_unlock_irqrestore(&xas, flags);

                btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
                percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
                                         -eb->len,
                                         fs_info->dirty_metadata_batch);
                ret = true;
        } else {
                spin_unlock(&eb->refs_lock);
        }
        btrfs_tree_unlock(eb);
        return ret;
}

static void set_btree_ioerr(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;

        set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);

        /*
         * A read may stumble upon this buffer later, make sure that it gets an
         * error and knows there was an error.
         */
        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

        /*
         * We need to set the mapping with the io error as well because a write
         * error will flip the file system readonly, and then syncfs() will
         * return a 0 because we are readonly if we don't modify the err seq for
         * the superblock.
         */
        mapping_set_error(eb->fs_info->btree_inode->i_mapping, -EIO);

        /*
         * If writeback for a btree extent that doesn't belong to a log tree
         * failed, increment the counter transaction->eb_write_errors.
         * We do this because while the transaction is running and before it's
         * committing (when we call filemap_fdata[write|wait]_range against
         * the btree inode), we might have
         * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
         * returns an error or an error happens during writeback, when we're
         * committing the transaction we wouldn't know about it, since the pages
         * can be no longer dirty nor marked anymore for writeback (if a
         * subsequent modification to the extent buffer didn't happen before the
         * transaction commit), which makes filemap_fdata[write|wait]_range not
         * able to find the pages which contain errors at transaction
         * commit time. So if this happens we must abort the transaction,
         * otherwise we commit a super block with btree roots that point to
         * btree nodes/leafs whose content on disk is invalid - either garbage
         * or the content of some node/leaf from a past generation that got
         * cowed or deleted and is no longer valid.
         *
         * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
         * not be enough - we need to distinguish between log tree extents vs
         * non-log tree extents, and the next filemap_fdatawait_range() call
         * will catch and clear such errors in the mapping - and that call might
         * be from a log sync and not from a transaction commit. Also, checking
         * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
         * not done and would not be reliable - the eb might have been released
         * from memory and reading it back again means that flag would not be
         * set (since it's a runtime flag, not persisted on disk).
         *
         * Using the flags below in the btree inode also makes us achieve the
         * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
         * writeback for all dirty pages and before filemap_fdatawait_range()
         * is called, the writeback for all dirty pages had already finished
         * with errors - because we were not using AS_EIO/AS_ENOSPC,
         * filemap_fdatawait_range() would return success, as it could not know
         * that writeback errors happened (the pages were no longer tagged for
         * writeback).
         */
        switch (eb->log_index) {
        case -1:
                set_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags);
                break;
        case 0:
                set_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
                break;
        case 1:
                set_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
                break;
        default:
                BUG(); /* unexpected, logic error */
        }
}

static void buffer_tree_set_mark(const struct extent_buffer *eb, xa_mark_t mark)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        XA_STATE(xas, &fs_info->buffer_tree, eb->start >> fs_info->nodesize_bits);
        unsigned long flags;

        xas_lock_irqsave(&xas, flags);
        xas_load(&xas);
        xas_set_mark(&xas, mark);
        xas_unlock_irqrestore(&xas, flags);
}

static void buffer_tree_clear_mark(const struct extent_buffer *eb, xa_mark_t mark)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        XA_STATE(xas, &fs_info->buffer_tree, eb->start >> fs_info->nodesize_bits);
        unsigned long flags;

        xas_lock_irqsave(&xas, flags);
        xas_load(&xas);
        xas_clear_mark(&xas, mark);
        xas_unlock_irqrestore(&xas, flags);
}

static void buffer_tree_tag_for_writeback(struct btrfs_fs_info *fs_info,
                                          unsigned long start, unsigned long end)
{
        XA_STATE(xas, &fs_info->buffer_tree, start);
        unsigned int tagged = 0;
        void *eb;

        xas_lock_irq(&xas);
        xas_for_each_marked(&xas, eb, end, PAGECACHE_TAG_DIRTY) {
                xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
                if (++tagged % XA_CHECK_SCHED)
                        continue;
                xas_pause(&xas);
                xas_unlock_irq(&xas);
                cond_resched();
                xas_lock_irq(&xas);
        }
        xas_unlock_irq(&xas);
}

struct eb_batch {
        unsigned int nr;
        unsigned int cur;
        struct extent_buffer *ebs[PAGEVEC_SIZE];
};

static inline bool eb_batch_add(struct eb_batch *batch, struct extent_buffer *eb)
{
        batch->ebs[batch->nr++] = eb;
        return (batch->nr < PAGEVEC_SIZE);
}

static inline void eb_batch_init(struct eb_batch *batch)
{
        batch->nr = 0;
        batch->cur = 0;
}

static inline struct extent_buffer *eb_batch_next(struct eb_batch *batch)
{
        if (batch->cur >= batch->nr)
                return NULL;
        return batch->ebs[batch->cur++];
}

static inline void eb_batch_release(struct eb_batch *batch)
{
        for (unsigned int i = 0; i < batch->nr; i++)
                free_extent_buffer(batch->ebs[i]);
        eb_batch_init(batch);
}

static inline struct extent_buffer *find_get_eb(struct xa_state *xas, unsigned long max,
                                                xa_mark_t mark)
{
        struct extent_buffer *eb;

retry:
        eb = xas_find_marked(xas, max, mark);

        if (xas_retry(xas, eb))
                goto retry;

        if (!eb)
                return NULL;

        if (!refcount_inc_not_zero(&eb->refs)) {
                xas_reset(xas);
                goto retry;
        }

        if (unlikely(eb != xas_reload(xas))) {
                free_extent_buffer(eb);
                xas_reset(xas);
                goto retry;
        }

        return eb;
}

static unsigned int buffer_tree_get_ebs_tag(struct btrfs_fs_info *fs_info,
                                            unsigned long *start,
                                            unsigned long end, xa_mark_t tag,
                                            struct eb_batch *batch)
{
        XA_STATE(xas, &fs_info->buffer_tree, *start);
        struct extent_buffer *eb;

        rcu_read_lock();
        while ((eb = find_get_eb(&xas, end, tag)) != NULL) {
                if (!eb_batch_add(batch, eb)) {
                        *start = ((eb->start + eb->len) >> fs_info->nodesize_bits);
                        goto out;
                }
        }
        if (end == ULONG_MAX)
                *start = ULONG_MAX;
        else
                *start = end + 1;
out:
        rcu_read_unlock();

        return batch->nr;
}

/*
 * The endio specific version which won't touch any unsafe spinlock in endio
 * context.
 */
static struct extent_buffer *find_extent_buffer_nolock(
                struct btrfs_fs_info *fs_info, u64 start)
{
        struct extent_buffer *eb;
        unsigned long index = (start >> fs_info->nodesize_bits);

        rcu_read_lock();
        eb = xa_load(&fs_info->buffer_tree, index);
        if (eb && !refcount_inc_not_zero(&eb->refs))
                eb = NULL;
        rcu_read_unlock();
        return eb;
}

static void end_bbio_meta_write(struct btrfs_bio *bbio)
{
        struct extent_buffer *eb = bbio->private;
        struct folio_iter fi;

        if (bbio->bio.bi_status != BLK_STS_OK)
                set_btree_ioerr(eb);

        bio_for_each_folio_all(fi, &bbio->bio) {
                btrfs_meta_folio_clear_writeback(fi.folio, eb);
        }

        buffer_tree_clear_mark(eb, PAGECACHE_TAG_WRITEBACK);
        clear_and_wake_up_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
        bio_put(&bbio->bio);
}

static void prepare_eb_write(struct extent_buffer *eb)
{
        u32 nritems;
        unsigned long start;
        unsigned long end;

        clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);

        /* Set btree blocks beyond nritems with 0 to avoid stale content */
        nritems = btrfs_header_nritems(eb);
        if (btrfs_header_level(eb) > 0) {
                end = btrfs_node_key_ptr_offset(eb, nritems);
                memzero_extent_buffer(eb, end, eb->len - end);
        } else {
                /*
                 * Leaf:
                 * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
                 */
                start = btrfs_item_nr_offset(eb, nritems);
                end = btrfs_item_nr_offset(eb, 0);
                if (nritems == 0)
                        end += BTRFS_LEAF_DATA_SIZE(eb->fs_info);
                else
                        end += btrfs_item_offset(eb, nritems - 1);
                memzero_extent_buffer(eb, start, end - start);
        }
}

static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
                                            struct writeback_control *wbc)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct btrfs_bio *bbio;

        prepare_eb_write(eb);

        bbio = btrfs_bio_alloc(INLINE_EXTENT_BUFFER_PAGES,
                               REQ_OP_WRITE | REQ_META | wbc_to_write_flags(wbc),
                               BTRFS_I(fs_info->btree_inode), eb->start,
                               end_bbio_meta_write, eb);
        bbio->bio.bi_iter.bi_sector = eb->start >> SECTOR_SHIFT;
        bio_set_dev(&bbio->bio, fs_info->fs_devices->latest_dev->bdev);
        wbc_init_bio(wbc, &bbio->bio);
        for (int i = 0; i < num_extent_folios(eb); i++) {
                struct folio *folio = eb->folios[i];
                u64 range_start = max_t(u64, eb->start, folio_pos(folio));
                u32 range_len = min_t(u64, folio_next_pos(folio),
                                      eb->start + eb->len) - range_start;

                folio_lock(folio);
                btrfs_meta_folio_clear_dirty(folio, eb);
                btrfs_meta_folio_set_writeback(folio, eb);
                if (!folio_test_dirty(folio))
                        wbc->nr_to_write -= folio_nr_pages(folio);
                bio_add_folio_nofail(&bbio->bio, folio, range_len,
                                     offset_in_folio(folio, range_start));
                wbc_account_cgroup_owner(wbc, folio, range_len);
                folio_unlock(folio);
        }
        /*
         * If the fs is already in error status, do not submit any writeback
         * but immediately finish it.
         */
        if (unlikely(BTRFS_FS_ERROR(fs_info))) {
                btrfs_bio_end_io(bbio, errno_to_blk_status(BTRFS_FS_ERROR(fs_info)));
                return;
        }
        btrfs_submit_bbio(bbio, 0);
}

/*
 * Wait for all eb writeback in the given range to finish.
 *
 * @fs_info:    The fs_info for this file system.
 * @start:      The offset of the range to start waiting on writeback.
 * @end:        The end of the range, inclusive. This is meant to be used in
 *              conjunction with wait_marked_extents, so this will usually be
 *              the_next_eb->start - 1.
 */
void btrfs_btree_wait_writeback_range(struct btrfs_fs_info *fs_info, u64 start,
                                      u64 end)
{
        struct eb_batch batch;
        unsigned long start_index = (start >> fs_info->nodesize_bits);
        unsigned long end_index = (end >> fs_info->nodesize_bits);

        eb_batch_init(&batch);
        while (start_index <= end_index) {
                struct extent_buffer *eb;
                unsigned int nr_ebs;

                nr_ebs = buffer_tree_get_ebs_tag(fs_info, &start_index, end_index,
                                                 PAGECACHE_TAG_WRITEBACK, &batch);
                if (!nr_ebs)
                        break;

                while ((eb = eb_batch_next(&batch)) != NULL)
                        wait_on_extent_buffer_writeback(eb);
                eb_batch_release(&batch);
                cond_resched();
        }
}

int btree_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct btrfs_eb_write_context ctx = { .wbc = wbc };
        struct btrfs_fs_info *fs_info = inode_to_fs_info(mapping->host);
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
        struct eb_batch batch;
        unsigned int nr_ebs;
        unsigned long index;
        unsigned long end;
        int scanned = 0;
        xa_mark_t tag;

        eb_batch_init(&batch);
        if (wbc->range_cyclic) {
                index = ((mapping->writeback_index << PAGE_SHIFT) >> fs_info->nodesize_bits);
                end = -1;

                /*
                 * Start from the beginning does not need to cycle over the
                 * range, mark it as scanned.
                 */
                scanned = (index == 0);
        } else {
                index = (wbc->range_start >> fs_info->nodesize_bits);
                end = (wbc->range_end >> fs_info->nodesize_bits);

                scanned = 1;
        }
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;
        btrfs_zoned_meta_io_lock(fs_info);
retry:
        if (wbc->sync_mode == WB_SYNC_ALL)
                buffer_tree_tag_for_writeback(fs_info, index, end);
        while (!done && !nr_to_write_done && (index <= end) &&
               (nr_ebs = buffer_tree_get_ebs_tag(fs_info, &index, end, tag, &batch))) {
                struct extent_buffer *eb;

                while ((eb = eb_batch_next(&batch)) != NULL) {
                        ctx.eb = eb;

                        ret = btrfs_check_meta_write_pointer(eb->fs_info, &ctx);
                        if (ret) {
                                if (ret == -EBUSY)
                                        ret = 0;

                                if (ret) {
                                        done = 1;
                                        break;
                                }
                                continue;
                        }

                        if (!lock_extent_buffer_for_io(eb, wbc))
                                continue;

                        /* Implies write in zoned mode. */
                        if (ctx.zoned_bg) {
                                /* Mark the last eb in the block group. */
                                btrfs_schedule_zone_finish_bg(ctx.zoned_bg, eb);
                                ctx.zoned_bg->meta_write_pointer += eb->len;
                        }
                        write_one_eb(eb, wbc);
                }
                nr_to_write_done = (wbc->nr_to_write <= 0);
                eb_batch_release(&batch);
                cond_resched();
        }
        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;
                goto retry;
        }
        /*
         * If something went wrong, don't allow any metadata write bio to be
         * submitted.
         *
         * This would prevent use-after-free if we had dirty pages not
         * cleaned up, which can still happen by fuzzed images.
         *
         * - Bad extent tree
         *   Allowing existing tree block to be allocated for other trees.
         *
         * - Log tree operations
         *   Exiting tree blocks get allocated to log tree, bumps its
         *   generation, then get cleaned in tree re-balance.
         *   Such tree block will not be written back, since it's clean,
         *   thus no WRITTEN flag set.
         *   And after log writes back, this tree block is not traced by
         *   any dirty extent_io_tree.
         *
         * - Offending tree block gets re-dirtied from its original owner
         *   Since it has bumped generation, no WRITTEN flag, it can be
         *   reused without COWing. This tree block will not be traced
         *   by btrfs_transaction::dirty_pages.
         *
         *   Now such dirty tree block will not be cleaned by any dirty
         *   extent io tree. Thus we don't want to submit such wild eb
         *   if the fs already has error.
         *
         * We can get ret > 0 from submit_extent_folio() indicating how many ebs
         * were submitted. Reset it to 0 to avoid false alerts for the caller.
         */
        if (ret > 0)
                ret = 0;
        if (!ret && BTRFS_FS_ERROR(fs_info))
                ret = -EROFS;

        if (ctx.zoned_bg)
                btrfs_put_block_group(ctx.zoned_bg);
        btrfs_zoned_meta_io_unlock(fs_info);
        return ret;
}

/*
 * Walk the list of dirty pages of the given address space and write all of them.
 *
 * @mapping:   address space structure to write
 * @wbc:       subtract the number of written pages from *@wbc->nr_to_write
 * @bio_ctrl:  holds context for the write, namely the bio
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
static int extent_write_cache_pages(struct address_space *mapping,
                             struct btrfs_bio_ctrl *bio_ctrl)
{
        struct writeback_control *wbc = bio_ctrl->wbc;
        struct inode *inode = mapping->host;
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
        struct folio_batch fbatch;
        unsigned int nr_folios;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        pgoff_t done_index;
        int range_whole = 0;
        int scanned = 0;
        xa_mark_t tag;

        /*
         * We have to hold onto the inode so that ordered extents can do their
         * work when the IO finishes.  The alternative to this is failing to add
         * an ordered extent if the igrab() fails there and that is a huge pain
         * to deal with, so instead just hold onto the inode throughout the
         * writepages operation.  If it fails here we are freeing up the inode
         * anyway and we'd rather not waste our time writing out stuff that is
         * going to be truncated anyway.
         */
        if (!igrab(inode))
                return 0;

        folio_batch_init(&fbatch);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
                /*
                 * Start from the beginning does not need to cycle over the
                 * range, mark it as scanned.
                 */
                scanned = (index == 0);
        } else {
                index = wbc->range_start >> PAGE_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                        range_whole = 1;
                scanned = 1;
        }

        /*
         * We do the tagged writepage as long as the snapshot flush bit is set
         * and we are the first one who do the filemap_flush() on this inode.
         *
         * The nr_to_write == LONG_MAX is needed to make sure other flushers do
         * not race in and drop the bit.
         */
        if (range_whole && wbc->nr_to_write == LONG_MAX &&
            test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH,
                               &BTRFS_I(inode)->runtime_flags))
                wbc->tagged_writepages = 1;

        tag = wbc_to_tag(wbc);
retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, index, end);
        done_index = index;
        while (!done && !nr_to_write_done && (index <= end) &&
                        (nr_folios = filemap_get_folios_tag(mapping, &index,
                                                        end, tag, &fbatch))) {
                unsigned i;

                for (i = 0; i < nr_folios; i++) {
                        struct folio *folio = fbatch.folios[i];

                        done_index = folio_next_index(folio);
                        /*
                         * At this point we hold neither the i_pages lock nor
                         * the folio lock: the folio may be truncated or
                         * invalidated (changing folio->mapping to NULL).
                         */
                        if (!folio_trylock(folio)) {
                                submit_write_bio(bio_ctrl, 0);
                                folio_lock(folio);
                        }

                        if (unlikely(folio->mapping != mapping)) {
                                folio_unlock(folio);
                                continue;
                        }

                        if (!folio_test_dirty(folio)) {
                                /* Someone wrote it for us. */
                                folio_unlock(folio);
                                continue;
                        }

                        /*
                         * For subpage case, compression can lead to mixed
                         * writeback and dirty flags, e.g:
                         * 0     32K    64K    96K    128K
                         * |     |//////||/////|   |//|
                         *
                         * In above case, [32K, 96K) is asynchronously submitted
                         * for compression, and [124K, 128K) needs to be written back.
                         *
                         * If we didn't wait writeback for page 64K, [128K, 128K)
                         * won't be submitted as the page still has writeback flag
                         * and will be skipped in the next check.
                         *
                         * This mixed writeback and dirty case is only possible for
                         * subpage case.
                         *
                         * TODO: Remove this check after migrating compression to
                         * regular submission.
                         */
                        if (wbc->sync_mode != WB_SYNC_NONE ||
                            btrfs_is_subpage(inode_to_fs_info(inode), folio)) {
                                if (folio_test_writeback(folio))
                                        submit_write_bio(bio_ctrl, 0);
                                folio_wait_writeback(folio);
                        }

                        if (folio_test_writeback(folio) ||
                            !folio_clear_dirty_for_io(folio)) {
                                folio_unlock(folio);
                                continue;
                        }

                        ret = extent_writepage(folio, bio_ctrl);
                        if (ret < 0) {
                                done = 1;
                                break;
                        }

                        /*
                         * The filesystem may choose to bump up nr_to_write.
                         * We have to make sure to honor the new nr_to_write
                         * at any time.
                         */
                        nr_to_write_done = (wbc->sync_mode == WB_SYNC_NONE &&
                                            wbc->nr_to_write <= 0);
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }
        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;

                /*
                 * If we're looping we could run into a page that is locked by a
                 * writer and that writer could be waiting on writeback for a
                 * page in our current bio, and thus deadlock, so flush the
                 * write bio here.
                 */
                submit_write_bio(bio_ctrl, 0);
                goto retry;
        }

        if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
                mapping->writeback_index = done_index;

        btrfs_add_delayed_iput(BTRFS_I(inode));
        return ret;
}

/*
 * Submit the pages in the range to bio for call sites which delalloc range has
 * already been ran (aka, ordered extent inserted) and all pages are still
 * locked.
 */
void extent_write_locked_range(struct inode *inode, const struct folio *locked_folio,
                               u64 start, u64 end, struct writeback_control *wbc,
                               bool pages_dirty)
{
        bool found_error = false;
        int ret = 0;
        struct address_space *mapping = inode->i_mapping;
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        const u32 sectorsize = fs_info->sectorsize;
        loff_t i_size = i_size_read(inode);
        u64 cur = start;
        struct btrfs_bio_ctrl bio_ctrl = {
                .wbc = wbc,
                .opf = REQ_OP_WRITE | wbc_to_write_flags(wbc),
        };

        if (wbc->no_cgroup_owner)
                bio_ctrl.opf |= REQ_BTRFS_CGROUP_PUNT;

        ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));

        while (cur <= end) {
                u64 cur_end;
                u32 cur_len;
                struct folio *folio;

                folio = filemap_get_folio(mapping, cur >> PAGE_SHIFT);

                /*
                 * This shouldn't happen, the pages are pinned and locked, this
                 * code is just in case, but shouldn't actually be run.
                 */
                if (IS_ERR(folio)) {
                        cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);
                        cur_len = cur_end + 1 - cur;
                        btrfs_mark_ordered_io_finished(BTRFS_I(inode), NULL,
                                                       cur, cur_len, false);
                        mapping_set_error(mapping, PTR_ERR(folio));
                        cur = cur_end;
                        continue;
                }

                cur_end = min_t(u64, folio_next_pos(folio) - 1, end);
                cur_len = cur_end + 1 - cur;

                ASSERT(folio_test_locked(folio));
                if (pages_dirty && folio != locked_folio)
                        ASSERT(folio_test_dirty(folio));

                /*
                 * Set the submission bitmap to submit all sectors.
                 * extent_writepage_io() will do the truncation correctly.
                 */
                bio_ctrl.submit_bitmap = (unsigned long)-1;
                ret = extent_writepage_io(BTRFS_I(inode), folio, cur, cur_len,
                                          &bio_ctrl, i_size);
                if (ret == 1)
                        goto next_page;

                if (ret)
                        mapping_set_error(mapping, ret);
                btrfs_folio_end_lock(fs_info, folio, cur, cur_len);
                if (ret < 0)
                        found_error = true;
next_page:
                folio_put(folio);
                cur = cur_end + 1;
        }

        submit_write_bio(&bio_ctrl, found_error ? ret : 0);
}

int btrfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        int ret = 0;
        struct btrfs_bio_ctrl bio_ctrl = {
                .wbc = wbc,
                .opf = REQ_OP_WRITE | wbc_to_write_flags(wbc),
        };

        /*
         * Allow only a single thread to do the reloc work in zoned mode to
         * protect the write pointer updates.
         */
        btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
        ret = extent_write_cache_pages(mapping, &bio_ctrl);
        submit_write_bio(&bio_ctrl, ret);
        btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
        return ret;
}

void btrfs_readahead(struct readahead_control *rac)
{
        struct btrfs_bio_ctrl bio_ctrl = {
                .opf = REQ_OP_READ | REQ_RAHEAD,
                .ractl = rac,
                .last_em_start = U64_MAX,
        };
        struct folio *folio;
        struct inode *vfs_inode = rac->mapping->host;
        struct btrfs_inode *inode = BTRFS_I(vfs_inode);
        const u64 start = readahead_pos(rac);
        const u64 end = start + readahead_length(rac) - 1;
        struct extent_state *cached_state = NULL;
        struct extent_map *em_cached = NULL;
        struct fsverity_info *vi = NULL;

        lock_extents_for_read(inode, start, end, &cached_state);
        if (start < i_size_read(vfs_inode))
                vi = fsverity_get_info(vfs_inode);
        while ((folio = readahead_folio(rac)) != NULL)
                btrfs_do_readpage(folio, &em_cached, &bio_ctrl, vi);

        btrfs_unlock_extent(&inode->io_tree, start, end, &cached_state);

        if (em_cached)
                btrfs_free_extent_map(em_cached);
        submit_one_bio(&bio_ctrl);
}

/*
 * basic invalidate_folio code, this waits on any locked or writeback
 * ranges corresponding to the folio, and then deletes any extent state
 * records from the tree
 */
int extent_invalidate_folio(struct extent_io_tree *tree,
                          struct folio *folio, size_t offset)
{
        struct extent_state *cached_state = NULL;
        u64 start = folio_pos(folio);
        u64 end = start + folio_size(folio) - 1;
        size_t blocksize = folio_to_fs_info(folio)->sectorsize;

        /* This function is only called for the btree inode */
        ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);

        start += ALIGN(offset, blocksize);
        if (start > end)
                return 0;

        btrfs_lock_extent(tree, start, end, &cached_state);
        folio_wait_writeback(folio);

        /*
         * Currently for btree io tree, only EXTENT_LOCKED is utilized,
         * so here we only need to unlock the extent range to free any
         * existing extent state.
         */
        btrfs_unlock_extent(tree, start, end, &cached_state);
        return 0;
}

/*
 * A helper for struct address_space_operations::release_folio, this tests for
 * areas of the folio that are locked or under IO and drops the related state
 * bits if it is safe to drop the folio.
 */
static bool try_release_extent_state(struct extent_io_tree *tree,
                                     struct folio *folio)
{
        struct extent_state *cached_state = NULL;
        u64 start = folio_pos(folio);
        u64 end = start + folio_size(folio) - 1;
        u32 range_bits;
        u32 clear_bits;
        bool ret = false;
        int ret2;

        btrfs_get_range_bits(tree, start, end, &range_bits, &cached_state);

        /*
         * We can release the folio if it's locked only for ordered extent
         * completion, since that doesn't require using the folio.
         */
        if ((range_bits & EXTENT_LOCKED) &&
            !(range_bits & EXTENT_FINISHING_ORDERED))
                goto out;

        clear_bits = ~(EXTENT_LOCKED | EXTENT_NODATASUM | EXTENT_DELALLOC_NEW |
                       EXTENT_CTLBITS | EXTENT_QGROUP_RESERVED |
                       EXTENT_FINISHING_ORDERED);
        /*
         * At this point we can safely clear everything except the locked,
         * nodatasum, delalloc new and finishing ordered bits. The delalloc new
         * bit will be cleared by ordered extent completion.
         */
        ret2 = btrfs_clear_extent_bit(tree, start, end, clear_bits, &cached_state);
        /*
         * If clear_extent_bit failed for enomem reasons, we can't allow the
         * release to continue.
         */
        if (ret2 == 0)
                ret = true;
out:
        btrfs_free_extent_state(cached_state);

        return ret;
}

/*
 * a helper for release_folio.  As long as there are no locked extents
 * in the range corresponding to the page, both state records and extent
 * map records are removed
 */
bool try_release_extent_mapping(struct folio *folio, gfp_t mask)
{
        u64 start = folio_pos(folio);
        u64 end = start + folio_size(folio) - 1;
        struct btrfs_inode *inode = folio_to_inode(folio);
        struct extent_io_tree *io_tree = &inode->io_tree;

        while (start <= end) {
                const u64 cur_gen = btrfs_get_fs_generation(inode->root->fs_info);
                const u64 len = end - start + 1;
                struct extent_map_tree *extent_tree = &inode->extent_tree;
                struct extent_map *em;

                write_lock(&extent_tree->lock);
                em = btrfs_lookup_extent_mapping(extent_tree, start, len);
                if (!em) {
                        write_unlock(&extent_tree->lock);
                        break;
                }
                if ((em->flags & EXTENT_FLAG_PINNED) || em->start != start) {
                        write_unlock(&extent_tree->lock);
                        btrfs_free_extent_map(em);
                        break;
                }
                if (btrfs_test_range_bit_exists(io_tree, em->start,
                                                btrfs_extent_map_end(em) - 1,
                                                EXTENT_LOCKED))
                        goto next;
                /*
                 * If it's not in the list of modified extents, used by a fast
                 * fsync, we can remove it. If it's being logged we can safely
                 * remove it since fsync took an extra reference on the em.
                 */
                if (list_empty(&em->list) || (em->flags & EXTENT_FLAG_LOGGING))
                        goto remove_em;
                /*
                 * If it's in the list of modified extents, remove it only if
                 * its generation is older then the current one, in which case
                 * we don't need it for a fast fsync. Otherwise don't remove it,
                 * we could be racing with an ongoing fast fsync that could miss
                 * the new extent.
                 */
                if (em->generation >= cur_gen)
                        goto next;
remove_em:
                /*
                 * We only remove extent maps that are not in the list of
                 * modified extents or that are in the list but with a
                 * generation lower then the current generation, so there is no
                 * need to set the full fsync flag on the inode (it hurts the
                 * fsync performance for workloads with a data size that exceeds
                 * or is close to the system's memory).
                 */
                btrfs_remove_extent_mapping(inode, em);
                /* Once for the inode's extent map tree. */
                btrfs_free_extent_map(em);
next:
                start = btrfs_extent_map_end(em);
                write_unlock(&extent_tree->lock);

                /* Once for us, for the lookup_extent_mapping() reference. */
                btrfs_free_extent_map(em);

                if (need_resched()) {
                        /*
                         * If we need to resched but we can't block just exit
                         * and leave any remaining extent maps.
                         */
                        if (!gfpflags_allow_blocking(mask))
                                break;

                        cond_resched();
                }
        }
        return try_release_extent_state(io_tree, folio);
}

static int extent_buffer_under_io(const struct extent_buffer *eb)
{
        return (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
                test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
}

static bool folio_range_has_eb(struct folio *folio)
{
        struct btrfs_folio_state *bfs;

        lockdep_assert_held(&folio->mapping->i_private_lock);

        if (folio_test_private(folio)) {
                bfs = folio_get_private(folio);
                if (atomic_read(&bfs->eb_refs))
                        return true;
        }
        return false;
}

static void detach_extent_buffer_folio(const struct extent_buffer *eb, struct folio *folio)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct address_space *mapping = folio->mapping;
        const bool mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

        /*
         * For mapped eb, we're going to change the folio private, which should
         * be done under the i_private_lock.
         */
        if (mapped)
                spin_lock(&mapping->i_private_lock);

        if (!folio_test_private(folio)) {
                if (mapped)
                        spin_unlock(&mapping->i_private_lock);
                return;
        }

        if (!btrfs_meta_is_subpage(fs_info)) {
                /*
                 * We do this since we'll remove the pages after we've removed
                 * the eb from the xarray, so we could race and have this page
                 * now attached to the new eb.  So only clear folio if it's
                 * still connected to this eb.
                 */
                if (folio_test_private(folio) && folio_get_private(folio) == eb) {
                        BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
                        BUG_ON(folio_test_dirty(folio));
                        BUG_ON(folio_test_writeback(folio));
                        /* We need to make sure we haven't be attached to a new eb. */
                        folio_detach_private(folio);
                }
                if (mapped)
                        spin_unlock(&mapping->i_private_lock);
                return;
        }

        /*
         * For subpage, we can have dummy eb with folio private attached.  In
         * this case, we can directly detach the private as such folio is only
         * attached to one dummy eb, no sharing.
         */
        if (!mapped) {
                btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);
                return;
        }

        btrfs_folio_dec_eb_refs(fs_info, folio);

        /*
         * We can only detach the folio private if there are no other ebs in the
         * page range and no unfinished IO.
         */
        if (!folio_range_has_eb(folio))
                btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);

        spin_unlock(&mapping->i_private_lock);
}

/* Release all folios attached to the extent buffer */
static void btrfs_release_extent_buffer_folios(const struct extent_buffer *eb)
{
        ASSERT(!extent_buffer_under_io(eb));

        for (int i = 0; i < INLINE_EXTENT_BUFFER_PAGES; i++) {
                struct folio *folio = eb->folios[i];

                if (!folio)
                        continue;

                detach_extent_buffer_folio(eb, folio);
        }
}

/*
 * Helper for releasing the extent buffer.
 */
static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
{
        btrfs_release_extent_buffer_folios(eb);
        btrfs_leak_debug_del_eb(eb);
        kmem_cache_free(extent_buffer_cache, eb);
}

static struct extent_buffer *__alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                                                   u64 start)
{
        struct extent_buffer *eb = NULL;

        eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
        eb->start = start;
        eb->len = fs_info->nodesize;
        eb->fs_info = fs_info;
        init_rwsem(&eb->lock);

        btrfs_leak_debug_add_eb(eb);

        spin_lock_init(&eb->refs_lock);
        refcount_set(&eb->refs, 1);

        ASSERT(eb->len <= BTRFS_MAX_METADATA_BLOCKSIZE);

        return eb;
}

/*
 * For use in eb allocation error cleanup paths, as btrfs_release_extent_buffer()
 * does not call folio_put(), and we need to set the folios to NULL so that
 * btrfs_release_extent_buffer() will not detach them a second time.
 */
static void cleanup_extent_buffer_folios(struct extent_buffer *eb)
{
        const int num_folios = num_extent_folios(eb);

        /* We cannot use num_extent_folios() as loop bound as eb->folios changes. */
        for (int i = 0; i < num_folios; i++) {
                ASSERT(eb->folios[i]);
                detach_extent_buffer_folio(eb, eb->folios[i]);
                folio_put(eb->folios[i]);
                eb->folios[i] = NULL;
        }
}

struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
{
        struct extent_buffer *new;
        int num_folios;
        int ret;

        new = __alloc_extent_buffer(src->fs_info, src->start);
        if (new == NULL)
                return NULL;

        /*
         * Set UNMAPPED before calling btrfs_release_extent_buffer(), as
         * btrfs_release_extent_buffer() have different behavior for
         * UNMAPPED subpage extent buffer.
         */
        set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);

        ret = alloc_eb_folio_array(new, false);
        if (ret)
                goto release_eb;

        ASSERT(num_extent_folios(src) == num_extent_folios(new),
               "%d != %d", num_extent_folios(src), num_extent_folios(new));
        /* Explicitly use the cached num_extent value from now on. */
        num_folios = num_extent_folios(src);
        for (int i = 0; i < num_folios; i++) {
                struct folio *folio = new->folios[i];

                ret = attach_extent_buffer_folio(new, folio, NULL);
                if (ret < 0)
                        goto cleanup_folios;
                WARN_ON(folio_test_dirty(folio));
        }
        for (int i = 0; i < num_folios; i++)
                folio_put(new->folios[i]);

        copy_extent_buffer_full(new, src);
        set_extent_buffer_uptodate(new);

        return new;

cleanup_folios:
        cleanup_extent_buffer_folios(new);
release_eb:
        btrfs_release_extent_buffer(new);
        return NULL;
}

struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                                                u64 start)
{
        struct extent_buffer *eb;
        int ret;

        eb = __alloc_extent_buffer(fs_info, start);
        if (!eb)
                return NULL;

        ret = alloc_eb_folio_array(eb, false);
        if (ret)
                goto release_eb;

        for (int i = 0; i < num_extent_folios(eb); i++) {
                ret = attach_extent_buffer_folio(eb, eb->folios[i], NULL);
                if (ret < 0)
                        goto cleanup_folios;
        }
        for (int i = 0; i < num_extent_folios(eb); i++)
                folio_put(eb->folios[i]);

        set_extent_buffer_uptodate(eb);
        btrfs_set_header_nritems(eb, 0);
        set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

        return eb;

cleanup_folios:
        cleanup_extent_buffer_folios(eb);
release_eb:
        btrfs_release_extent_buffer(eb);
        return NULL;
}

static void check_buffer_tree_ref(struct extent_buffer *eb)
{
        int refs;
        /*
         * The TREE_REF bit is first set when the extent_buffer is added to the
         * xarray. It is also reset, if unset, when a new reference is created
         * by find_extent_buffer.
         *
         * It is only cleared in two cases: freeing the last non-tree
         * reference to the extent_buffer when its STALE bit is set or
         * calling release_folio when the tree reference is the only reference.
         *
         * In both cases, care is taken to ensure that the extent_buffer's
         * pages are not under io. However, release_folio can be concurrently
         * called with creating new references, which is prone to race
         * conditions between the calls to check_buffer_tree_ref in those
         * codepaths and clearing TREE_REF in try_release_extent_buffer.
         *
         * The actual lifetime of the extent_buffer in the xarray is adequately
         * protected by the refcount, but the TREE_REF bit and its corresponding
         * reference are not. To protect against this class of races, we call
         * check_buffer_tree_ref() from the code paths which trigger io. Note that
         * once io is initiated, TREE_REF can no longer be cleared, so that is
         * the moment at which any such race is best fixed.
         */
        refs = refcount_read(&eb->refs);
        if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                return;

        spin_lock(&eb->refs_lock);
        if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                refcount_inc(&eb->refs);
        spin_unlock(&eb->refs_lock);
}

static void mark_extent_buffer_accessed(struct extent_buffer *eb)
{
        check_buffer_tree_ref(eb);

        for (int i = 0; i < num_extent_folios(eb); i++)
                folio_mark_accessed(eb->folios[i]);
}

struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
                                         u64 start)
{
        struct extent_buffer *eb;

        eb = find_extent_buffer_nolock(fs_info, start);
        if (!eb)
                return NULL;
        /*
         * Lock our eb's refs_lock to avoid races with free_extent_buffer().
         * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
         * another task running free_extent_buffer() might have seen that flag
         * set, eb->refs == 2, that the buffer isn't under IO (dirty and
         * writeback flags not set) and it's still in the tree (flag
         * EXTENT_BUFFER_TREE_REF set), therefore being in the process of
         * decrementing the extent buffer's reference count twice.  So here we
         * could race and increment the eb's reference count, clear its stale
         * flag, mark it as dirty and drop our reference before the other task
         * finishes executing free_extent_buffer, which would later result in
         * an attempt to free an extent buffer that is dirty.
         */
        if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
                spin_lock(&eb->refs_lock);
                spin_unlock(&eb->refs_lock);
        }
        mark_extent_buffer_accessed(eb);
        return eb;
}

struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
                                        u64 start)
{
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
        struct extent_buffer *eb, *exists = NULL;
        int ret;

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;
        eb = alloc_dummy_extent_buffer(fs_info, start);
        if (!eb)
                return ERR_PTR(-ENOMEM);
        eb->fs_info = fs_info;
again:
        xa_lock_irq(&fs_info->buffer_tree);
        exists = __xa_cmpxchg(&fs_info->buffer_tree, start >> fs_info->nodesize_bits,
                              NULL, eb, GFP_NOFS);
        if (xa_is_err(exists)) {
                ret = xa_err(exists);
                xa_unlock_irq(&fs_info->buffer_tree);
                btrfs_release_extent_buffer(eb);
                return ERR_PTR(ret);
        }
        if (exists) {
                if (!refcount_inc_not_zero(&exists->refs)) {
                        /* The extent buffer is being freed, retry. */
                        xa_unlock_irq(&fs_info->buffer_tree);
                        goto again;
                }
                xa_unlock_irq(&fs_info->buffer_tree);
                btrfs_release_extent_buffer(eb);
                return exists;
        }
        xa_unlock_irq(&fs_info->buffer_tree);
        check_buffer_tree_ref(eb);

        return eb;
#else
        /* Stub to avoid linker error when compiled with optimizations turned off. */
        return NULL;
#endif
}

static struct extent_buffer *grab_extent_buffer(struct btrfs_fs_info *fs_info,
                                                struct folio *folio)
{
        struct extent_buffer *exists;

        lockdep_assert_held(&folio->mapping->i_private_lock);

        /*
         * For subpage case, we completely rely on xarray to ensure we don't try
         * to insert two ebs for the same bytenr.  So here we always return NULL
         * and just continue.
         */
        if (btrfs_meta_is_subpage(fs_info))
                return NULL;

        /* Page not yet attached to an extent buffer */
        if (!folio_test_private(folio))
                return NULL;

        /*
         * We could have already allocated an eb for this folio and attached one
         * so lets see if we can get a ref on the existing eb, and if we can we
         * know it's good and we can just return that one, else we know we can
         * just overwrite folio private.
         */
        exists = folio_get_private(folio);
        if (refcount_inc_not_zero(&exists->refs))
                return exists;

        WARN_ON(folio_test_dirty(folio));
        folio_detach_private(folio);
        return NULL;
}

/*
 * Validate alignment constraints of eb at logical address @start.
 */
static bool check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
{
        const u32 nodesize = fs_info->nodesize;

        if (unlikely(!IS_ALIGNED(start, fs_info->sectorsize))) {
                btrfs_err(fs_info, "bad tree block start %llu", start);
                return true;
        }

        if (unlikely(nodesize < PAGE_SIZE && !IS_ALIGNED(start, nodesize))) {
                btrfs_err(fs_info,
                "tree block is not nodesize aligned, start %llu nodesize %u",
                          start, nodesize);
                return true;
        }
        if (unlikely(nodesize >= PAGE_SIZE && !PAGE_ALIGNED(start))) {
                btrfs_err(fs_info,
                "tree block is not page aligned, start %llu nodesize %u",
                          start, nodesize);
                return true;
        }
        if (unlikely(!IS_ALIGNED(start, nodesize) &&
                     !test_and_set_bit(BTRFS_FS_UNALIGNED_TREE_BLOCK, &fs_info->flags))) {
                btrfs_warn(fs_info,
"tree block not nodesize aligned, start %llu nodesize %u, can be resolved by a full metadata balance",
                              start, nodesize);
        }
        return false;
}

/*
 * Return 0 if eb->folios[i] is attached to btree inode successfully.
 * Return >0 if there is already another extent buffer for the range,
 * and @found_eb_ret would be updated.
 * Return -EAGAIN if the filemap has an existing folio but with different size
 * than @eb.
 * The caller needs to free the existing folios and retry using the same order.
 */
static int attach_eb_folio_to_filemap(struct extent_buffer *eb, int i,
                                      struct btrfs_folio_state *prealloc,
                                      struct extent_buffer **found_eb_ret)
{

        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct address_space *mapping = fs_info->btree_inode->i_mapping;
        const pgoff_t index = eb->start >> PAGE_SHIFT;
        struct folio *existing_folio;
        int ret;

        ASSERT(found_eb_ret);

        /* Caller should ensure the folio exists. */
        ASSERT(eb->folios[i]);

retry:
        existing_folio = NULL;
        ret = filemap_add_folio(mapping, eb->folios[i], index + i,
                                GFP_NOFS | __GFP_NOFAIL);
        if (!ret)
                goto finish;

        existing_folio = filemap_lock_folio(mapping, index + i);
        /* The page cache only exists for a very short time, just retry. */
        if (IS_ERR(existing_folio))
                goto retry;

        /* For now, we should only have single-page folios for btree inode. */
        ASSERT(folio_nr_pages(existing_folio) == 1);

        if (folio_size(existing_folio) != eb->folio_size) {
                folio_unlock(existing_folio);
                folio_put(existing_folio);
                return -EAGAIN;
        }

finish:
        spin_lock(&mapping->i_private_lock);
        if (existing_folio && btrfs_meta_is_subpage(fs_info)) {
                /* We're going to reuse the existing page, can drop our folio now. */
                __free_page(folio_page(eb->folios[i], 0));
                eb->folios[i] = existing_folio;
        } else if (existing_folio) {
                struct extent_buffer *existing_eb;

                existing_eb = grab_extent_buffer(fs_info, existing_folio);
                if (existing_eb) {
                        /* The extent buffer still exists, we can use it directly. */
                        *found_eb_ret = existing_eb;
                        spin_unlock(&mapping->i_private_lock);
                        folio_unlock(existing_folio);
                        folio_put(existing_folio);
                        return 1;
                }
                /* The extent buffer no longer exists, we can reuse the folio. */
                __free_page(folio_page(eb->folios[i], 0));
                eb->folios[i] = existing_folio;
        }
        eb->folio_size = folio_size(eb->folios[i]);
        eb->folio_shift = folio_shift(eb->folios[i]);
        /* Should not fail, as we have preallocated the memory. */
        ret = attach_extent_buffer_folio(eb, eb->folios[i], prealloc);
        ASSERT(!ret);
        /*
         * To inform we have an extra eb under allocation, so that
         * detach_extent_buffer_page() won't release the folio private when the
         * eb hasn't been inserted into the xarray yet.
         *
         * The ref will be decreased when the eb releases the page, in
         * detach_extent_buffer_page().  Thus needs no special handling in the
         * error path.
         */
        btrfs_folio_inc_eb_refs(fs_info, eb->folios[i]);
        spin_unlock(&mapping->i_private_lock);
        return 0;
}

struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                                          u64 start, u64 owner_root, int level)
{
        int attached = 0;
        struct extent_buffer *eb;
        struct extent_buffer *existing_eb = NULL;
        struct btrfs_folio_state *prealloc = NULL;
        u64 lockdep_owner = owner_root;
        bool page_contig = true;
        int uptodate = 1;
        int ret;

        if (check_eb_alignment(fs_info, start))
                return ERR_PTR(-EINVAL);

#if BITS_PER_LONG == 32
        if (start >= MAX_LFS_FILESIZE) {
                btrfs_err_rl(fs_info,
                "extent buffer %llu is beyond 32bit page cache limit", start);
                btrfs_err_32bit_limit(fs_info);
                return ERR_PTR(-EOVERFLOW);
        }
        if (start >= BTRFS_32BIT_EARLY_WARN_THRESHOLD)
                btrfs_warn_32bit_limit(fs_info);
#endif

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;

        eb = __alloc_extent_buffer(fs_info, start);
        if (!eb)
                return ERR_PTR(-ENOMEM);

        /*
         * The reloc trees are just snapshots, so we need them to appear to be
         * just like any other fs tree WRT lockdep.
         */
        if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID)
                lockdep_owner = BTRFS_FS_TREE_OBJECTID;

        btrfs_set_buffer_lockdep_class(lockdep_owner, eb, level);

        /*
         * Preallocate folio private for subpage case, so that we won't
         * allocate memory with i_private_lock nor page lock hold.
         *
         * The memory will be freed by attach_extent_buffer_page() or freed
         * manually if we exit earlier.
         */
        if (btrfs_meta_is_subpage(fs_info)) {
                prealloc = btrfs_alloc_folio_state(fs_info, PAGE_SIZE, BTRFS_SUBPAGE_METADATA);
                if (IS_ERR(prealloc)) {
                        ret = PTR_ERR(prealloc);
                        goto out;
                }
        }

reallocate:
        /* Allocate all pages first. */
        ret = alloc_eb_folio_array(eb, true);
        if (ret < 0) {
                btrfs_free_folio_state(prealloc);
                goto out;
        }

        /* Attach all pages to the filemap. */
        for (int i = 0; i < num_extent_folios(eb); i++) {
                struct folio *folio;

                ret = attach_eb_folio_to_filemap(eb, i, prealloc, &existing_eb);
                if (ret > 0) {
                        ASSERT(existing_eb);
                        goto out;
                }

                /*
                 * TODO: Special handling for a corner case where the order of
                 * folios mismatch between the new eb and filemap.
                 *
                 * This happens when:
                 *
                 * - the new eb is using higher order folio
                 *
                 * - the filemap is still using 0-order folios for the range
                 *   This can happen at the previous eb allocation, and we don't
                 *   have higher order folio for the call.
                 *
                 * - the existing eb has already been freed
                 *
                 * In this case, we have to free the existing folios first, and
                 * re-allocate using the same order.
                 * Thankfully this is not going to happen yet, as we're still
                 * using 0-order folios.
                 */
                if (unlikely(ret == -EAGAIN)) {
                        DEBUG_WARN("folio order mismatch between new eb and filemap");
                        goto reallocate;
                }
                attached++;

                /*
                 * Only after attach_eb_folio_to_filemap(), eb->folios[] is
                 * reliable, as we may choose to reuse the existing page cache
                 * and free the allocated page.
                 */
                folio = eb->folios[i];
                WARN_ON(btrfs_meta_folio_test_dirty(folio, eb));

                /*
                 * Check if the current page is physically contiguous with previous eb
                 * page.
                 * At this stage, either we allocated a large folio, thus @i
                 * would only be 0, or we fall back to per-page allocation.
                 */
                if (i && folio_page(eb->folios[i - 1], 0) + 1 != folio_page(folio, 0))
                        page_contig = false;

                if (!btrfs_meta_folio_test_uptodate(folio, eb))
                        uptodate = 0;

                /*
                 * We can't unlock the pages just yet since the extent buffer
                 * hasn't been properly inserted into the xarray, this opens a
                 * race with btree_release_folio() which can free a page while we
                 * are still filling in all pages for the buffer and we could crash.
                 */
        }
        if (uptodate)
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        /* All pages are physically contiguous, can skip cross page handling. */
        if (page_contig)
                eb->addr = folio_address(eb->folios[0]) + offset_in_page(eb->start);
again:
        xa_lock_irq(&fs_info->buffer_tree);
        existing_eb = __xa_cmpxchg(&fs_info->buffer_tree,
                                   start >> fs_info->nodesize_bits, NULL, eb,
                                   GFP_NOFS);
        if (xa_is_err(existing_eb)) {
                ret = xa_err(existing_eb);
                xa_unlock_irq(&fs_info->buffer_tree);
                goto out;
        }
        if (existing_eb) {
                if (!refcount_inc_not_zero(&existing_eb->refs)) {
                        xa_unlock_irq(&fs_info->buffer_tree);
                        goto again;
                }
                xa_unlock_irq(&fs_info->buffer_tree);
                goto out;
        }
        xa_unlock_irq(&fs_info->buffer_tree);

        /* add one reference for the tree */
        check_buffer_tree_ref(eb);

        /*
         * Now it's safe to unlock the pages because any calls to
         * btree_release_folio will correctly detect that a page belongs to a
         * live buffer and won't free them prematurely.
         */
        for (int i = 0; i < num_extent_folios(eb); i++) {
                folio_unlock(eb->folios[i]);
                /*
                 * A folio that has been added to an address_space mapping
                 * should not continue holding the refcount from its original
                 * allocation indefinitely.
                 */
                folio_put(eb->folios[i]);
        }
        return eb;

out:
        WARN_ON(!refcount_dec_and_test(&eb->refs));

        /*
         * Any attached folios need to be detached before we unlock them.  This
         * is because when we're inserting our new folios into the mapping, and
         * then attaching our eb to that folio.  If we fail to insert our folio
         * we'll lookup the folio for that index, and grab that EB.  We do not
         * want that to grab this eb, as we're getting ready to free it.  So we
         * have to detach it first and then unlock it.
         *
         * Note: the bounds is num_extent_pages() as we need to go through all slots.
         */
        for (int i = 0; i < num_extent_pages(eb); i++) {
                struct folio *folio = eb->folios[i];

                if (i < attached) {
                        ASSERT(folio);
                        detach_extent_buffer_folio(eb, folio);
                        folio_unlock(folio);
                } else if (!folio) {
                        continue;
                }

                folio_put(folio);
                eb->folios[i] = NULL;
        }
        btrfs_release_extent_buffer(eb);
        if (ret < 0)
                return ERR_PTR(ret);
        ASSERT(existing_eb);
        return existing_eb;
}

static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
{
        struct extent_buffer *eb =
                        container_of(head, struct extent_buffer, rcu_head);

        kmem_cache_free(extent_buffer_cache, eb);
}

static int release_extent_buffer(struct extent_buffer *eb)
        __releases(&eb->refs_lock)
{
        lockdep_assert_held(&eb->refs_lock);

        if (refcount_dec_and_test(&eb->refs)) {
                struct btrfs_fs_info *fs_info = eb->fs_info;

                spin_unlock(&eb->refs_lock);

                /*
                 * We're erasing, theoretically there will be no allocations, so
                 * just use GFP_ATOMIC.
                 *
                 * We use cmpxchg instead of erase because we do not know if
                 * this eb is actually in the tree or not, we could be cleaning
                 * up an eb that we allocated but never inserted into the tree.
                 * Thus use cmpxchg to remove it from the tree if it is there,
                 * or leave the other entry if this isn't in the tree.
                 *
                 * The documentation says that putting a NULL value is the same
                 * as erase as long as XA_FLAGS_ALLOC is not set, which it isn't
                 * in this case.
                 */
                xa_cmpxchg_irq(&fs_info->buffer_tree,
                               eb->start >> fs_info->nodesize_bits, eb, NULL,
                               GFP_ATOMIC);

                btrfs_leak_debug_del_eb(eb);
                /* Should be safe to release folios at this point. */
                btrfs_release_extent_buffer_folios(eb);
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
                if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
                        kmem_cache_free(extent_buffer_cache, eb);
                        return 1;
                }
#endif
                call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
                return 1;
        }
        spin_unlock(&eb->refs_lock);

        return 0;
}

void free_extent_buffer(struct extent_buffer *eb)
{
        int refs;
        if (!eb)
                return;

        refs = refcount_read(&eb->refs);
        while (1) {
                if (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags)) {
                        if (refs == 1)
                                break;
                } else if (refs <= 3) {
                        break;
                }

                /* Optimization to avoid locking eb->refs_lock. */
                if (atomic_try_cmpxchg(&eb->refs.refs, &refs, refs - 1))
                        return;
        }

        spin_lock(&eb->refs_lock);
        if (refcount_read(&eb->refs) == 2 &&
            test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
            !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                refcount_dec(&eb->refs);

        /*
         * I know this is terrible, but it's temporary until we stop tracking
         * the uptodate bits and such for the extent buffers.
         */
        release_extent_buffer(eb);
}

void free_extent_buffer_stale(struct extent_buffer *eb)
{
        if (!eb)
                return;

        spin_lock(&eb->refs_lock);
        set_bit(EXTENT_BUFFER_STALE, &eb->bflags);

        if (refcount_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                refcount_dec(&eb->refs);
        release_extent_buffer(eb);
}

static void btree_clear_folio_dirty_tag(struct folio *folio)
{
        ASSERT(!folio_test_dirty(folio));
        ASSERT(folio_test_locked(folio));
        xa_lock_irq(&folio->mapping->i_pages);
        if (!folio_test_dirty(folio))
                __xa_clear_mark(&folio->mapping->i_pages, folio->index,
                                PAGECACHE_TAG_DIRTY);
        xa_unlock_irq(&folio->mapping->i_pages);
}

void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
                              struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;

        btrfs_assert_tree_write_locked(eb);

        if (trans && btrfs_header_generation(eb) != trans->transid)
                return;

        /*
         * Instead of clearing the dirty flag off of the buffer, mark it as
         * EXTENT_BUFFER_ZONED_ZEROOUT. This allows us to preserve
         * write-ordering in zoned mode, without the need to later re-dirty
         * the extent_buffer.
         *
         * The actual zeroout of the buffer will happen later in
         * btree_csum_one_bio.
         */
        if (btrfs_is_zoned(fs_info) && test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                set_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags);
                return;
        }

        if (!test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
                return;

        buffer_tree_clear_mark(eb, PAGECACHE_TAG_DIRTY);
        percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, -eb->len,
                                 fs_info->dirty_metadata_batch);

        for (int i = 0; i < num_extent_folios(eb); i++) {
                struct folio *folio = eb->folios[i];
                bool last;

                if (!folio_test_dirty(folio))
                        continue;
                folio_lock(folio);
                last = btrfs_meta_folio_clear_and_test_dirty(folio, eb);
                if (last)
                        btree_clear_folio_dirty_tag(folio);
                folio_unlock(folio);
        }
        WARN_ON(refcount_read(&eb->refs) == 0);
}

void set_extent_buffer_dirty(struct extent_buffer *eb)
{
        bool was_dirty;

        check_buffer_tree_ref(eb);

        was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);

        WARN_ON(refcount_read(&eb->refs) == 0);
        WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));
        WARN_ON(test_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags));

        if (!was_dirty) {
                bool subpage = btrfs_meta_is_subpage(eb->fs_info);

                /*
                 * For subpage case, we can have other extent buffers in the
                 * same page, and in clear_extent_buffer_dirty() we
                 * have to clear page dirty without subpage lock held.
                 * This can cause race where our page gets dirty cleared after
                 * we just set it.
                 *
                 * Thankfully, clear_extent_buffer_dirty() has locked
                 * its page for other reasons, we can use page lock to prevent
                 * the above race.
                 */
                if (subpage)
                        folio_lock(eb->folios[0]);
                for (int i = 0; i < num_extent_folios(eb); i++)
                        btrfs_meta_folio_set_dirty(eb->folios[i], eb);
                buffer_tree_set_mark(eb, PAGECACHE_TAG_DIRTY);
                if (subpage)
                        folio_unlock(eb->folios[0]);
                percpu_counter_add_batch(&eb->fs_info->dirty_metadata_bytes,
                                         eb->len,
                                         eb->fs_info->dirty_metadata_batch);
        }
#ifdef CONFIG_BTRFS_DEBUG
        for (int i = 0; i < num_extent_folios(eb); i++)
                ASSERT(folio_test_dirty(eb->folios[i]));
#endif
}

void clear_extent_buffer_uptodate(struct extent_buffer *eb)
{

        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        for (int i = 0; i < num_extent_folios(eb); i++) {
                struct folio *folio = eb->folios[i];

                if (!folio)
                        continue;

                btrfs_meta_folio_clear_uptodate(folio, eb);
        }
}

void set_extent_buffer_uptodate(struct extent_buffer *eb)
{

        set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        for (int i = 0; i < num_extent_folios(eb); i++)
                btrfs_meta_folio_set_uptodate(eb->folios[i], eb);
}

static void clear_extent_buffer_reading(struct extent_buffer *eb)
{
        clear_and_wake_up_bit(EXTENT_BUFFER_READING, &eb->bflags);
}

static void end_bbio_meta_read(struct btrfs_bio *bbio)
{
        struct extent_buffer *eb = bbio->private;
        bool uptodate = !bbio->bio.bi_status;

        /*
         * If the extent buffer is marked UPTODATE before the read operation
         * completes, other calls to read_extent_buffer_pages() will return
         * early without waiting for the read to finish, causing data races.
         */
        WARN_ON(test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags));

        eb->read_mirror = bbio->mirror_num;

        if (uptodate &&
            btrfs_validate_extent_buffer(eb, &bbio->parent_check) < 0)
                uptodate = false;

        if (uptodate)
                set_extent_buffer_uptodate(eb);
        else
                clear_extent_buffer_uptodate(eb);

        clear_extent_buffer_reading(eb);
        free_extent_buffer(eb);

        bio_put(&bbio->bio);
}

int read_extent_buffer_pages_nowait(struct extent_buffer *eb, int mirror_num,
                                    const struct btrfs_tree_parent_check *check)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct btrfs_bio *bbio;

        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 0;

        /*
         * We could have had EXTENT_BUFFER_UPTODATE cleared by the write
         * operation, which could potentially still be in flight.  In this case
         * we simply want to return an error.
         */
        if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
                return -EIO;

        /* Someone else is already reading the buffer, just wait for it. */
        if (test_and_set_bit(EXTENT_BUFFER_READING, &eb->bflags))
                return 0;

        /*
         * Between the initial test_bit(EXTENT_BUFFER_UPTODATE) and the above
         * test_and_set_bit(EXTENT_BUFFER_READING), someone else could have
         * started and finished reading the same eb.  In this case, UPTODATE
         * will now be set, and we shouldn't read it in again.
         */
        if (unlikely(test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))) {
                clear_extent_buffer_reading(eb);
                return 0;
        }

        eb->read_mirror = 0;
        check_buffer_tree_ref(eb);
        refcount_inc(&eb->refs);

        bbio = btrfs_bio_alloc(INLINE_EXTENT_BUFFER_PAGES,
                               REQ_OP_READ | REQ_META, BTRFS_I(fs_info->btree_inode),
                               eb->start, end_bbio_meta_read, eb);
        bbio->bio.bi_iter.bi_sector = eb->start >> SECTOR_SHIFT;
        memcpy(&bbio->parent_check, check, sizeof(*check));
        for (int i = 0; i < num_extent_folios(eb); i++) {
                struct folio *folio = eb->folios[i];
                u64 range_start = max_t(u64, eb->start, folio_pos(folio));
                u32 range_len = min_t(u64, folio_next_pos(folio),
                                      eb->start + eb->len) - range_start;

                bio_add_folio_nofail(&bbio->bio, folio, range_len,
                                     offset_in_folio(folio, range_start));
        }
        btrfs_submit_bbio(bbio, mirror_num);
        return 0;
}

int read_extent_buffer_pages(struct extent_buffer *eb, int mirror_num,
                             const struct btrfs_tree_parent_check *check)
{
        int ret;

        ret = read_extent_buffer_pages_nowait(eb, mirror_num, check);
        if (ret < 0)
                return ret;

        wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_READING, TASK_UNINTERRUPTIBLE);
        if (unlikely(!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags)))
                return -EIO;
        return 0;
}

static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
                            unsigned long len)
{
        btrfs_warn(eb->fs_info,
                "access to eb bytenr %llu len %u out of range start %lu len %lu",
                eb->start, eb->len, start, len);
        DEBUG_WARN();

        return true;
}

/*
 * Check if the [start, start + len) range is valid before reading/writing
 * the eb.
 * NOTE: @start and @len are offset inside the eb, not logical address.
 *
 * Caller should not touch the dst/src memory if this function returns error.
 */
static inline int check_eb_range(const struct extent_buffer *eb,
                                 unsigned long start, unsigned long len)
{
        unsigned long offset;

        /* start, start + len should not go beyond eb->len nor overflow */
        if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
                return report_eb_range(eb, start, len);

        return false;
}

void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
                        unsigned long start, unsigned long len)
{
        const int unit_size = eb->folio_size;
        size_t cur;
        size_t offset;
        char *dst = (char *)dstv;
        unsigned long i = get_eb_folio_index(eb, start);

        if (check_eb_range(eb, start, len)) {
                /*
                 * Invalid range hit, reset the memory, so callers won't get
                 * some random garbage for their uninitialized memory.
                 */
                memset(dstv, 0, len);
                return;
        }

        if (eb->addr) {
                memcpy(dstv, eb->addr + start, len);
                return;
        }

        offset = get_eb_offset_in_folio(eb, start);

        while (len > 0) {
                char *kaddr;

                cur = min(len, unit_size - offset);
                kaddr = folio_address(eb->folios[i]);
                memcpy(dst, kaddr + offset, cur);

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
                                       void __user *dstv,
                                       unsigned long start, unsigned long len)
{
        const int unit_size = eb->folio_size;
        size_t cur;
        size_t offset;
        char __user *dst = (char __user *)dstv;
        unsigned long i = get_eb_folio_index(eb, start);
        int ret = 0;

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        if (eb->addr) {
                if (copy_to_user_nofault(dstv, eb->addr + start, len))
                        ret = -EFAULT;
                return ret;
        }

        offset = get_eb_offset_in_folio(eb, start);

        while (len > 0) {
                char *kaddr;

                cur = min(len, unit_size - offset);
                kaddr = folio_address(eb->folios[i]);
                if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
                        ret = -EFAULT;
                        break;
                }

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }

        return ret;
}

int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
                         unsigned long start, unsigned long len)
{
        const int unit_size = eb->folio_size;
        size_t cur;
        size_t offset;
        char *kaddr;
        char *ptr = (char *)ptrv;
        unsigned long i = get_eb_folio_index(eb, start);
        int ret = 0;

        if (check_eb_range(eb, start, len))
                return -EINVAL;

        if (eb->addr)
                return memcmp(ptrv, eb->addr + start, len);

        offset = get_eb_offset_in_folio(eb, start);

        while (len > 0) {
                cur = min(len, unit_size - offset);
                kaddr = folio_address(eb->folios[i]);
                ret = memcmp(ptr, kaddr + offset, cur);
                if (ret)
                        break;

                ptr += cur;
                len -= cur;
                offset = 0;
                i++;
        }
        return ret;
}

/*
 * Check that the extent buffer is uptodate.
 *
 * For regular sector size == PAGE_SIZE case, check if @page is uptodate.
 * For subpage case, check if the range covered by the eb has EXTENT_UPTODATE.
 */
static void assert_eb_folio_uptodate(const struct extent_buffer *eb, int i)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct folio *folio = eb->folios[i];

        ASSERT(folio);

        /*
         * If we are using the commit root we could potentially clear a page
         * Uptodate while we're using the extent buffer that we've previously
         * looked up.  We don't want to complain in this case, as the page was
         * valid before, we just didn't write it out.  Instead we want to catch
         * the case where we didn't actually read the block properly, which
         * would have !PageUptodate and !EXTENT_BUFFER_WRITE_ERR.
         */
        if (test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
                return;

        if (btrfs_meta_is_subpage(fs_info)) {
                folio = eb->folios[0];
                ASSERT(i == 0);
                if (WARN_ON(!btrfs_subpage_test_uptodate(fs_info, folio,
                                                         eb->start, eb->len)))
                        btrfs_subpage_dump_bitmap(fs_info, folio, eb->start, eb->len);
        } else {
                WARN_ON(!folio_test_uptodate(folio));
        }
}

static void __write_extent_buffer(const struct extent_buffer *eb,
                                  const void *srcv, unsigned long start,
                                  unsigned long len, bool use_memmove)
{
        const int unit_size = eb->folio_size;
        size_t cur;
        size_t offset;
        char *kaddr;
        const char *src = (const char *)srcv;
        unsigned long i = get_eb_folio_index(eb, start);
        /* For unmapped (dummy) ebs, no need to check their uptodate status. */
        const bool check_uptodate = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

        if (check_eb_range(eb, start, len))
                return;

        if (eb->addr) {
                if (use_memmove)
                        memmove(eb->addr + start, srcv, len);
                else
                        memcpy(eb->addr + start, srcv, len);
                return;
        }

        offset = get_eb_offset_in_folio(eb, start);

        while (len > 0) {
                if (check_uptodate)
                        assert_eb_folio_uptodate(eb, i);

                cur = min(len, unit_size - offset);
                kaddr = folio_address(eb->folios[i]);
                if (use_memmove)
                        memmove(kaddr + offset, src, cur);
                else
                        memcpy(kaddr + offset, src, cur);

                src += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

void write_extent_buffer(const struct extent_buffer *eb, const void *srcv,
                         unsigned long start, unsigned long len)
{
        return __write_extent_buffer(eb, srcv, start, len, false);
}

static void memset_extent_buffer(const struct extent_buffer *eb, int c,
                                 unsigned long start, unsigned long len)
{
        const int unit_size = eb->folio_size;
        unsigned long cur = start;

        if (eb->addr) {
                memset(eb->addr + start, c, len);
                return;
        }

        while (cur < start + len) {
                unsigned long index = get_eb_folio_index(eb, cur);
                unsigned int offset = get_eb_offset_in_folio(eb, cur);
                unsigned int cur_len = min(start + len - cur, unit_size - offset);

                assert_eb_folio_uptodate(eb, index);
                memset(folio_address(eb->folios[index]) + offset, c, cur_len);

                cur += cur_len;
        }
}

void memzero_extent_buffer(const struct extent_buffer *eb, unsigned long start,
                           unsigned long len)
{
        if (check_eb_range(eb, start, len))
                return;
        return memset_extent_buffer(eb, 0, start, len);
}

void copy_extent_buffer_full(const struct extent_buffer *dst,
                             const struct extent_buffer *src)
{
        const int unit_size = src->folio_size;
        unsigned long cur = 0;

        ASSERT(dst->len == src->len);

        while (cur < src->len) {
                unsigned long index = get_eb_folio_index(src, cur);
                unsigned long offset = get_eb_offset_in_folio(src, cur);
                unsigned long cur_len = min(src->len, unit_size - offset);
                void *addr = folio_address(src->folios[index]) + offset;

                write_extent_buffer(dst, addr, cur, cur_len);

                cur += cur_len;
        }
}

void copy_extent_buffer(const struct extent_buffer *dst,
                        const struct extent_buffer *src,
                        unsigned long dst_offset, unsigned long src_offset,
                        unsigned long len)
{
        const int unit_size = dst->folio_size;
        u64 dst_len = dst->len;
        size_t cur;
        size_t offset;
        char *kaddr;
        unsigned long i = get_eb_folio_index(dst, dst_offset);

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(src, src_offset, len))
                return;

        WARN_ON(src->len != dst_len);

        offset = get_eb_offset_in_folio(dst, dst_offset);

        while (len > 0) {
                assert_eb_folio_uptodate(dst, i);

                cur = min(len, (unsigned long)(unit_size - offset));

                kaddr = folio_address(dst->folios[i]);
                read_extent_buffer(src, kaddr + offset, src_offset, cur);

                src_offset += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

/*
 * Calculate the folio and offset of the byte containing the given bit number.
 *
 * @eb:           the extent buffer
 * @start:        offset of the bitmap item in the extent buffer
 * @nr:           bit number
 * @folio_index:  return index of the folio in the extent buffer that contains
 *                the given bit number
 * @folio_offset: return offset into the folio given by folio_index
 *
 * This helper hides the ugliness of finding the byte in an extent buffer which
 * contains a given bit.
 */
static inline void eb_bitmap_offset(const struct extent_buffer *eb,
                                    unsigned long start, unsigned long nr,
                                    unsigned long *folio_index,
                                    size_t *folio_offset)
{
        size_t byte_offset = BIT_BYTE(nr);
        size_t offset;

        /*
         * The byte we want is the offset of the extent buffer + the offset of
         * the bitmap item in the extent buffer + the offset of the byte in the
         * bitmap item.
         */
        offset = start + offset_in_eb_folio(eb, eb->start) + byte_offset;

        *folio_index = offset >> eb->folio_shift;
        *folio_offset = offset_in_eb_folio(eb, offset);
}

/*
 * Determine whether a bit in a bitmap item is set.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @nr:     bit number to test
 */
bool extent_buffer_test_bit(const struct extent_buffer *eb, unsigned long start,
                            unsigned long nr)
{
        unsigned long i;
        size_t offset;
        u8 *kaddr;

        eb_bitmap_offset(eb, start, nr, &i, &offset);
        assert_eb_folio_uptodate(eb, i);
        kaddr = folio_address(eb->folios[i]);
        return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
}

static u8 *extent_buffer_get_byte(const struct extent_buffer *eb, unsigned long bytenr)
{
        unsigned long index = get_eb_folio_index(eb, bytenr);

        if (check_eb_range(eb, bytenr, 1))
                return NULL;
        return folio_address(eb->folios[index]) + get_eb_offset_in_folio(eb, bytenr);
}

/*
 * Set an area of a bitmap to 1.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to set
 */
void extent_buffer_bitmap_set(const struct extent_buffer *eb, unsigned long start,
                              unsigned long pos, unsigned long len)
{
        unsigned int first_byte = start + BIT_BYTE(pos);
        unsigned int last_byte = start + BIT_BYTE(pos + len - 1);
        const bool same_byte = (first_byte == last_byte);
        u8 mask = BITMAP_FIRST_BYTE_MASK(pos);
        u8 *kaddr;

        if (same_byte)
                mask &= BITMAP_LAST_BYTE_MASK(pos + len);

        /* Handle the first byte. */
        kaddr = extent_buffer_get_byte(eb, first_byte);
        *kaddr |= mask;
        if (same_byte)
                return;

        /* Handle the byte aligned part. */
        ASSERT(first_byte + 1 <= last_byte);
        memset_extent_buffer(eb, 0xff, first_byte + 1, last_byte - first_byte - 1);

        /* Handle the last byte. */
        kaddr = extent_buffer_get_byte(eb, last_byte);
        *kaddr |= BITMAP_LAST_BYTE_MASK(pos + len);
}


/*
 * Clear an area of a bitmap.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to clear
 */
void extent_buffer_bitmap_clear(const struct extent_buffer *eb,
                                unsigned long start, unsigned long pos,
                                unsigned long len)
{
        unsigned int first_byte = start + BIT_BYTE(pos);
        unsigned int last_byte = start + BIT_BYTE(pos + len - 1);
        const bool same_byte = (first_byte == last_byte);
        u8 mask = BITMAP_FIRST_BYTE_MASK(pos);
        u8 *kaddr;

        if (same_byte)
                mask &= BITMAP_LAST_BYTE_MASK(pos + len);

        /* Handle the first byte. */
        kaddr = extent_buffer_get_byte(eb, first_byte);
        *kaddr &= ~mask;
        if (same_byte)
                return;

        /* Handle the byte aligned part. */
        ASSERT(first_byte + 1 <= last_byte);
        memset_extent_buffer(eb, 0, first_byte + 1, last_byte - first_byte - 1);

        /* Handle the last byte. */
        kaddr = extent_buffer_get_byte(eb, last_byte);
        *kaddr &= ~BITMAP_LAST_BYTE_MASK(pos + len);
}

static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
{
        unsigned long distance = (src > dst) ? src - dst : dst - src;
        return distance < len;
}

void memcpy_extent_buffer(const struct extent_buffer *dst,
                          unsigned long dst_offset, unsigned long src_offset,
                          unsigned long len)
{
        const int unit_size = dst->folio_size;
        unsigned long cur_off = 0;

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(dst, src_offset, len))
                return;

        if (dst->addr) {
                const bool use_memmove = areas_overlap(src_offset, dst_offset, len);

                if (use_memmove)
                        memmove(dst->addr + dst_offset, dst->addr + src_offset, len);
                else
                        memcpy(dst->addr + dst_offset, dst->addr + src_offset, len);
                return;
        }

        while (cur_off < len) {
                unsigned long cur_src = cur_off + src_offset;
                unsigned long folio_index = get_eb_folio_index(dst, cur_src);
                unsigned long folio_off = get_eb_offset_in_folio(dst, cur_src);
                unsigned long cur_len = min(src_offset + len - cur_src,
                                            unit_size - folio_off);
                void *src_addr = folio_address(dst->folios[folio_index]) + folio_off;
                const bool use_memmove = areas_overlap(src_offset + cur_off,
                                                       dst_offset + cur_off, cur_len);

                __write_extent_buffer(dst, src_addr, dst_offset + cur_off, cur_len,
                                      use_memmove);
                cur_off += cur_len;
        }
}

void memmove_extent_buffer(const struct extent_buffer *dst,
                           unsigned long dst_offset, unsigned long src_offset,
                           unsigned long len)
{
        unsigned long dst_end = dst_offset + len - 1;
        unsigned long src_end = src_offset + len - 1;

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(dst, src_offset, len))
                return;

        if (dst_offset < src_offset) {
                memcpy_extent_buffer(dst, dst_offset, src_offset, len);
                return;
        }

        if (dst->addr) {
                memmove(dst->addr + dst_offset, dst->addr + src_offset, len);
                return;
        }

        while (len > 0) {
                unsigned long src_i;
                size_t cur;
                size_t dst_off_in_folio;
                size_t src_off_in_folio;
                void *src_addr;
                bool use_memmove;

                src_i = get_eb_folio_index(dst, src_end);

                dst_off_in_folio = get_eb_offset_in_folio(dst, dst_end);
                src_off_in_folio = get_eb_offset_in_folio(dst, src_end);

                cur = min_t(unsigned long, len, src_off_in_folio + 1);
                cur = min(cur, dst_off_in_folio + 1);

                src_addr = folio_address(dst->folios[src_i]) + src_off_in_folio -
                                         cur + 1;
                use_memmove = areas_overlap(src_end - cur + 1, dst_end - cur + 1,
                                            cur);

                __write_extent_buffer(dst, src_addr, dst_end - cur + 1, cur,
                                      use_memmove);

                dst_end -= cur;
                src_end -= cur;
                len -= cur;
        }
}

static int try_release_subpage_extent_buffer(struct folio *folio)
{
        struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
        struct extent_buffer *eb;
        unsigned long start = (folio_pos(folio) >> fs_info->nodesize_bits);
        unsigned long index = start;
        unsigned long end = index + (PAGE_SIZE >> fs_info->nodesize_bits) - 1;
        int ret;

        rcu_read_lock();
        xa_for_each_range(&fs_info->buffer_tree, index, eb, start, end) {
                /*
                 * The same as try_release_extent_buffer(), to ensure the eb
                 * won't disappear out from under us.
                 */
                spin_lock(&eb->refs_lock);
                rcu_read_unlock();

                if (refcount_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
                        spin_unlock(&eb->refs_lock);
                        rcu_read_lock();
                        continue;
                }

                /*
                 * If tree ref isn't set then we know the ref on this eb is a
                 * real ref, so just return, this eb will likely be freed soon
                 * anyway.
                 */
                if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
                        spin_unlock(&eb->refs_lock);
                        rcu_read_lock();
                        break;
                }

                /*
                 * Here we don't care about the return value, we will always
                 * check the folio private at the end.  And
                 * release_extent_buffer() will release the refs_lock.
                 */
                release_extent_buffer(eb);
                rcu_read_lock();
        }
        rcu_read_unlock();

        /*
         * Finally to check if we have cleared folio private, as if we have
         * released all ebs in the page, the folio private should be cleared now.
         */
        spin_lock(&folio->mapping->i_private_lock);
        if (!folio_test_private(folio))
                ret = 1;
        else
                ret = 0;
        spin_unlock(&folio->mapping->i_private_lock);
        return ret;
}

int try_release_extent_buffer(struct folio *folio)
{
        struct extent_buffer *eb;

        if (btrfs_meta_is_subpage(folio_to_fs_info(folio)))
                return try_release_subpage_extent_buffer(folio);

        /*
         * We need to make sure nobody is changing folio private, as we rely on
         * folio private as the pointer to extent buffer.
         */
        spin_lock(&folio->mapping->i_private_lock);
        if (!folio_test_private(folio)) {
                spin_unlock(&folio->mapping->i_private_lock);
                return 1;
        }

        eb = folio_get_private(folio);
        BUG_ON(!eb);

        /*
         * This is a little awful but should be ok, we need to make sure that
         * the eb doesn't disappear out from under us while we're looking at
         * this page.
         */
        spin_lock(&eb->refs_lock);
        if (refcount_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
                spin_unlock(&eb->refs_lock);
                spin_unlock(&folio->mapping->i_private_lock);
                return 0;
        }
        spin_unlock(&folio->mapping->i_private_lock);

        /*
         * If tree ref isn't set then we know the ref on this eb is a real ref,
         * so just return, this page will likely be freed soon anyway.
         */
        if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
                spin_unlock(&eb->refs_lock);
                return 0;
        }

        return release_extent_buffer(eb);
}

/*
 * Attempt to readahead a child block.
 *
 * @fs_info:    the fs_info
 * @bytenr:     bytenr to read
 * @owner_root: objectid of the root that owns this eb
 * @gen:        generation for the uptodate check, can be 0
 * @level:      level for the eb
 *
 * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
 * normal uptodate check of the eb, without checking the generation.  If we have
 * to read the block we will not block on anything.
 */
void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
                                u64 bytenr, u64 owner_root, u64 gen, int level)
{
        struct btrfs_tree_parent_check check = {
                .level = level,
                .transid = gen
        };
        struct extent_buffer *eb;
        int ret;

        eb = btrfs_find_create_tree_block(fs_info, bytenr, owner_root, level);
        if (IS_ERR(eb))
                return;

        if (btrfs_buffer_uptodate(eb, gen, true)) {
                free_extent_buffer(eb);
                return;
        }

        ret = read_extent_buffer_pages_nowait(eb, 0, &check);
        if (ret < 0)
                free_extent_buffer_stale(eb);
        else
                free_extent_buffer(eb);
}

/*
 * Readahead a node's child block.
 *
 * @node:       parent node we're reading from
 * @slot:       slot in the parent node for the child we want to read
 *
 * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
 * the slot in the node provided.
 */
void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
{
        btrfs_readahead_tree_block(node->fs_info,
                                   btrfs_node_blockptr(node, slot),
                                   btrfs_header_owner(node),
                                   btrfs_node_ptr_generation(node, slot),
                                   btrfs_header_level(node) - 1);
}