// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2010 Red Hat, Inc.
 * Copyright (C) 2016-2023 Christoph Hellwig.
 */
#include <linux/iomap.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/fserror.h>
#include "internal.h"
#include "trace.h"

#include "../internal.h"

/*
 * Structure allocated for each folio to track per-block uptodate, dirty state
 * and I/O completions.
 */
struct iomap_folio_state {
        spinlock_t              state_lock;
        unsigned int            read_bytes_pending;
        atomic_t                write_bytes_pending;

        /*
         * Each block has two bits in this bitmap:
         * Bits [0..blocks_per_folio) has the uptodate status.
         * Bits [b_p_f...(2*b_p_f))   has the dirty status.
         */
        unsigned long           state[];
};

static inline bool ifs_is_fully_uptodate(struct folio *folio,
                struct iomap_folio_state *ifs)
{
        struct inode *inode = folio->mapping->host;

        return bitmap_full(ifs->state, i_blocks_per_folio(inode, folio));
}

/*
 * Find the next uptodate block in the folio. end_blk is inclusive.
 * If no uptodate block is found, this will return end_blk + 1.
 */
static unsigned ifs_next_uptodate_block(struct folio *folio,
                unsigned start_blk, unsigned end_blk)
{
        struct iomap_folio_state *ifs = folio->private;

        return find_next_bit(ifs->state, end_blk + 1, start_blk);
}

/*
 * Find the next non-uptodate block in the folio. end_blk is inclusive.
 * If no non-uptodate block is found, this will return end_blk + 1.
 */
static unsigned ifs_next_nonuptodate_block(struct folio *folio,
                unsigned start_blk, unsigned end_blk)
{
        struct iomap_folio_state *ifs = folio->private;

        return find_next_zero_bit(ifs->state, end_blk + 1, start_blk);
}

static bool ifs_set_range_uptodate(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int first_blk = off >> inode->i_blkbits;
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;

        bitmap_set(ifs->state, first_blk, nr_blks);
        return ifs_is_fully_uptodate(folio, ifs);
}

static void iomap_set_range_uptodate(struct folio *folio, size_t off,
                size_t len)
{
        struct iomap_folio_state *ifs = folio->private;
        unsigned long flags;
        bool mark_uptodate = true;

        if (folio_test_uptodate(folio))
                return;

        if (ifs) {
                spin_lock_irqsave(&ifs->state_lock, flags);
                /*
                 * If a read with bytes pending is in progress, we must not call
                 * folio_mark_uptodate(). The read completion path
                 * (iomap_read_end()) will call folio_end_read(), which uses XOR
                 * semantics to set the uptodate bit. If we set it here, the XOR
                 * in folio_end_read() will clear it, leaving the folio not
                 * uptodate.
                 */
                mark_uptodate = ifs_set_range_uptodate(folio, ifs, off, len) &&
                                !ifs->read_bytes_pending;
                spin_unlock_irqrestore(&ifs->state_lock, flags);
        }

        if (mark_uptodate)
                folio_mark_uptodate(folio);
}

/*
 * Find the next dirty block in the folio. end_blk is inclusive.
 * If no dirty block is found, this will return end_blk + 1.
 */
static unsigned ifs_next_dirty_block(struct folio *folio,
                unsigned start_blk, unsigned end_blk)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = folio->mapping->host;
        unsigned int blks = i_blocks_per_folio(inode, folio);

        return find_next_bit(ifs->state, blks + end_blk + 1,
                        blks + start_blk) - blks;
}

/*
 * Find the next clean block in the folio. end_blk is inclusive.
 * If no clean block is found, this will return end_blk + 1.
 */
static unsigned ifs_next_clean_block(struct folio *folio,
                unsigned start_blk, unsigned end_blk)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = folio->mapping->host;
        unsigned int blks = i_blocks_per_folio(inode, folio);

        return find_next_zero_bit(ifs->state, blks + end_blk + 1,
                        blks + start_blk) - blks;
}

static unsigned ifs_find_dirty_range(struct folio *folio,
                struct iomap_folio_state *ifs, u64 *range_start, u64 range_end)
{
        struct inode *inode = folio->mapping->host;
        unsigned start_blk =
                offset_in_folio(folio, *range_start) >> inode->i_blkbits;
        unsigned end_blk = min_not_zero(
                offset_in_folio(folio, range_end) >> inode->i_blkbits,
                i_blocks_per_folio(inode, folio)) - 1;
        unsigned nblks;

        start_blk = ifs_next_dirty_block(folio, start_blk, end_blk);
        if (start_blk > end_blk)
                return 0;
        if (start_blk == end_blk)
                nblks = 1;
        else
                nblks = ifs_next_clean_block(folio, start_blk + 1, end_blk) -
                                start_blk;

        *range_start = folio_pos(folio) + (start_blk << inode->i_blkbits);
        return nblks << inode->i_blkbits;
}

static unsigned iomap_find_dirty_range(struct folio *folio, u64 *range_start,
                u64 range_end)
{
        struct iomap_folio_state *ifs = folio->private;

        if (*range_start >= range_end)
                return 0;

        if (ifs)
                return ifs_find_dirty_range(folio, ifs, range_start, range_end);
        return range_end - *range_start;
}

static void ifs_clear_range_dirty(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
        unsigned int first_blk = (off >> inode->i_blkbits);
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;
        unsigned long flags;

        spin_lock_irqsave(&ifs->state_lock, flags);
        bitmap_clear(ifs->state, first_blk + blks_per_folio, nr_blks);
        spin_unlock_irqrestore(&ifs->state_lock, flags);
}

static void iomap_clear_range_dirty(struct folio *folio, size_t off, size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs)
                ifs_clear_range_dirty(folio, ifs, off, len);
}

static void ifs_set_range_dirty(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
        unsigned int first_blk = (off >> inode->i_blkbits);
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;
        unsigned long flags;

        spin_lock_irqsave(&ifs->state_lock, flags);
        bitmap_set(ifs->state, first_blk + blks_per_folio, nr_blks);
        spin_unlock_irqrestore(&ifs->state_lock, flags);
}

static void iomap_set_range_dirty(struct folio *folio, size_t off, size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs)
                ifs_set_range_dirty(folio, ifs, off, len);
}

static struct iomap_folio_state *ifs_alloc(struct inode *inode,
                struct folio *folio, unsigned int flags)
{
        struct iomap_folio_state *ifs = folio->private;
        unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
        gfp_t gfp;

        if (ifs || nr_blocks <= 1)
                return ifs;

        if (flags & IOMAP_NOWAIT)
                gfp = GFP_NOWAIT;
        else
                gfp = GFP_NOFS | __GFP_NOFAIL;

        /*
         * ifs->state tracks two sets of state flags when the
         * filesystem block size is smaller than the folio size.
         * The first state tracks per-block uptodate and the
         * second tracks per-block dirty state.
         */
        ifs = kzalloc_flex(*ifs, state, BITS_TO_LONGS(2 * nr_blocks), gfp);
        if (!ifs)
                return ifs;

        spin_lock_init(&ifs->state_lock);
        if (folio_test_uptodate(folio))
                bitmap_set(ifs->state, 0, nr_blocks);
        if (folio_test_dirty(folio))
                bitmap_set(ifs->state, nr_blocks, nr_blocks);
        folio_attach_private(folio, ifs);

        return ifs;
}

static void ifs_free(struct folio *folio)
{
        struct iomap_folio_state *ifs = folio_detach_private(folio);

        if (!ifs)
                return;
        WARN_ON_ONCE(ifs->read_bytes_pending != 0);
        WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending));
        WARN_ON_ONCE(ifs_is_fully_uptodate(folio, ifs) !=
                        folio_test_uptodate(folio));
        kfree(ifs);
}

/*
 * Calculate how many bytes to truncate based off the number of blocks to
 * truncate and the end position to start truncating from.
 */
static size_t iomap_bytes_to_truncate(loff_t end_pos, unsigned block_bits,
                unsigned blocks_truncated)
{
        unsigned block_size = 1 << block_bits;
        unsigned block_offset = end_pos & (block_size - 1);

        if (!block_offset)
                return blocks_truncated << block_bits;

        return ((blocks_truncated - 1) << block_bits) + block_offset;
}

/*
 * Calculate the range inside the folio that we actually need to read.
 */
static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
                loff_t *pos, loff_t length, size_t *offp, size_t *lenp)
{
        struct iomap_folio_state *ifs = folio->private;
        loff_t orig_pos = *pos;
        loff_t isize = i_size_read(inode);
        unsigned block_bits = inode->i_blkbits;
        unsigned block_size = (1 << block_bits);
        size_t poff = offset_in_folio(folio, *pos);
        size_t plen = min_t(loff_t, folio_size(folio) - poff, length);
        size_t orig_plen = plen;
        unsigned first = poff >> block_bits;
        unsigned last = (poff + plen - 1) >> block_bits;

        /*
         * If the block size is smaller than the page size, we need to check the
         * per-block uptodate status and adjust the offset and length if needed
         * to avoid reading in already uptodate ranges.
         */
        if (ifs) {
                unsigned int next, blocks_skipped;

                next = ifs_next_nonuptodate_block(folio, first, last);
                blocks_skipped = next - first;

                if (blocks_skipped) {
                        unsigned long block_offset = *pos & (block_size - 1);
                        unsigned bytes_skipped =
                                (blocks_skipped << block_bits) - block_offset;

                        *pos += bytes_skipped;
                        poff += bytes_skipped;
                        plen -= bytes_skipped;
                }
                first = next;

                /* truncate len if we find any trailing uptodate block(s) */
                if (++next <= last) {
                        next = ifs_next_uptodate_block(folio, next, last);
                        if (next <= last) {
                                plen -= iomap_bytes_to_truncate(*pos + plen,
                                                block_bits, last - next + 1);
                                last = next - 1;
                        }
                }
        }

        /*
         * If the extent spans the block that contains the i_size, we need to
         * handle both halves separately so that we properly zero data in the
         * page cache for blocks that are entirely outside of i_size.
         */
        if (orig_pos <= isize && orig_pos + orig_plen > isize) {
                unsigned end = offset_in_folio(folio, isize - 1) >> block_bits;

                if (first <= end && last > end)
                        plen -= iomap_bytes_to_truncate(*pos + plen, block_bits,
                                        last - end);
        }

        *offp = poff;
        *lenp = plen;
}

static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
                loff_t pos)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);

        return srcmap->type != IOMAP_MAPPED ||
                (srcmap->flags & IOMAP_F_NEW) ||
                pos >= i_size_read(iter->inode);
}

/**
 * iomap_read_inline_data - copy inline data into the page cache
 * @iter: iteration structure
 * @folio: folio to copy to
 *
 * Copy the inline data in @iter into @folio and zero out the rest of the folio.
 * Only a single IOMAP_INLINE extent is allowed at the end of each file.
 * Returns zero for success to complete the read, or the usual negative errno.
 */
static int iomap_read_inline_data(const struct iomap_iter *iter,
                struct folio *folio)
{
        const struct iomap *iomap = iomap_iter_srcmap(iter);
        size_t size = i_size_read(iter->inode) - iomap->offset;
        size_t offset = offset_in_folio(folio, iomap->offset);

        if (WARN_ON_ONCE(!iomap->inline_data))
                return -EIO;

        if (folio_test_uptodate(folio))
                return 0;

        if (WARN_ON_ONCE(size > iomap->length)) {
                fserror_report_io(iter->inode, FSERR_BUFFERED_READ,
                                  iomap->offset, size, -EIO, GFP_NOFS);
                return -EIO;
        }
        if (offset > 0)
                ifs_alloc(iter->inode, folio, iter->flags);

        folio_fill_tail(folio, offset, iomap->inline_data, size);
        iomap_set_range_uptodate(folio, offset, folio_size(folio) - offset);
        return 0;
}

void iomap_finish_folio_read(struct folio *folio, size_t off, size_t len,
                int error)
{
        struct iomap_folio_state *ifs = folio->private;
        bool uptodate = !error;
        bool finished = true;

        if (ifs) {
                unsigned long flags;

                spin_lock_irqsave(&ifs->state_lock, flags);
                if (!error)
                        uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
                ifs->read_bytes_pending -= len;
                finished = !ifs->read_bytes_pending;
                spin_unlock_irqrestore(&ifs->state_lock, flags);
        }

        if (error)
                fserror_report_io(folio->mapping->host, FSERR_BUFFERED_READ,
                                  folio_pos(folio) + off, len, error,
                                  GFP_ATOMIC);

        if (finished)
                folio_end_read(folio, uptodate);
}
EXPORT_SYMBOL_GPL(iomap_finish_folio_read);

static void iomap_read_init(struct folio *folio)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs) {
                /*
                 * ifs->read_bytes_pending is used to track how many bytes are
                 * read in asynchronously by the IO helper. We need to track
                 * this so that we can know when the IO helper has finished
                 * reading in all the necessary ranges of the folio and can end
                 * the read.
                 *
                 * Increase ->read_bytes_pending by the folio size to start.
                 * We'll subtract any uptodate / zeroed ranges that did not
                 * require IO in iomap_read_end() after we're done processing
                 * the folio.
                 *
                 * We do this because otherwise, we would have to increment
                 * ifs->read_bytes_pending every time a range in the folio needs
                 * to be read in, which can get expensive since the spinlock
                 * needs to be held whenever modifying ifs->read_bytes_pending.
                 */
                spin_lock_irq(&ifs->state_lock);
                WARN_ON_ONCE(ifs->read_bytes_pending != 0);
                ifs->read_bytes_pending = folio_size(folio);
                spin_unlock_irq(&ifs->state_lock);
        }
}

/*
 * This ends IO if no bytes were submitted to an IO helper.
 *
 * Otherwise, this calibrates ifs->read_bytes_pending to represent only the
 * submitted bytes (see comment in iomap_read_init()). If all bytes submitted
 * have already been completed by the IO helper, then this will end the read.
 * Else the IO helper will end the read after all submitted ranges have been
 * read.
 */
static void iomap_read_end(struct folio *folio, size_t bytes_submitted)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs) {
                bool end_read, uptodate;

                spin_lock_irq(&ifs->state_lock);
                if (!ifs->read_bytes_pending) {
                        WARN_ON_ONCE(bytes_submitted);
                        spin_unlock_irq(&ifs->state_lock);
                        folio_unlock(folio);
                        return;
                }

                /*
                 * Subtract any bytes that were initially accounted to
                 * read_bytes_pending but skipped for IO.
                 */
                ifs->read_bytes_pending -= folio_size(folio) - bytes_submitted;

                /*
                 * If !ifs->read_bytes_pending, this means all pending reads by
                 * the IO helper have already completed, which means we need to
                 * end the folio read here. If ifs->read_bytes_pending != 0,
                 * the IO helper will end the folio read.
                 */
                end_read = !ifs->read_bytes_pending;
                if (end_read)
                        uptodate = ifs_is_fully_uptodate(folio, ifs);
                spin_unlock_irq(&ifs->state_lock);
                if (end_read)
                        folio_end_read(folio, uptodate);
        } else {
                /*
                 * If a folio without an ifs is submitted to the IO helper, the
                 * read must be on the entire folio and the IO helper takes
                 * ownership of the folio. This means we should only enter
                 * iomap_read_end() for the !ifs case if no bytes were submitted
                 * to the IO helper, in which case we are responsible for
                 * unlocking the folio here.
                 */
                WARN_ON_ONCE(bytes_submitted);
                folio_unlock(folio);
        }
}

static int iomap_read_folio_iter(struct iomap_iter *iter,
                struct iomap_read_folio_ctx *ctx, size_t *bytes_submitted)
{
        const struct iomap *iomap = &iter->iomap;
        loff_t pos = iter->pos;
        loff_t length = iomap_length(iter);
        struct folio *folio = ctx->cur_folio;
        size_t folio_len = folio_size(folio);
        struct iomap_folio_state *ifs;
        size_t poff, plen;
        loff_t pos_diff;
        int ret;

        if (iomap->type == IOMAP_INLINE) {
                ret = iomap_read_inline_data(iter, folio);
                if (ret)
                        return ret;
                return iomap_iter_advance(iter, length);
        }

        ifs = ifs_alloc(iter->inode, folio, iter->flags);

        length = min_t(loff_t, length, folio_len - offset_in_folio(folio, pos));
        while (length) {
                iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff,
                                &plen);

                pos_diff = pos - iter->pos;
                if (WARN_ON_ONCE(pos_diff + plen > length))
                        return -EIO;

                ret = iomap_iter_advance(iter, pos_diff);
                if (ret)
                        return ret;

                if (plen == 0)
                        return 0;

                /* zero post-eof blocks as the page may be mapped */
                if (iomap_block_needs_zeroing(iter, pos)) {
                        folio_zero_range(folio, poff, plen);
                        iomap_set_range_uptodate(folio, poff, plen);
                } else {
                        if (!*bytes_submitted)
                                iomap_read_init(folio);
                        ret = ctx->ops->read_folio_range(iter, ctx, plen);
                        if (ret < 0)
                                fserror_report_io(iter->inode,
                                                  FSERR_BUFFERED_READ, pos,
                                                  plen, ret, GFP_NOFS);
                        if (ret)
                                return ret;

                        *bytes_submitted += plen;
                        /*
                         * Hand off folio ownership to the IO helper when:
                         * 1) The entire folio has been submitted for IO, or
                         * 2) There is no ifs attached to the folio
                         *
                         * Case (2) occurs when 1 << i_blkbits matches the folio
                         * size but the underlying filesystem or block device
                         * uses a smaller granularity for IO.
                         */
                        if (*bytes_submitted == folio_len || !ifs)
                                ctx->cur_folio = NULL;
                }

                ret = iomap_iter_advance(iter, plen);
                if (ret)
                        return ret;
                length -= pos_diff + plen;
                pos = iter->pos;
        }
        return 0;
}

void iomap_read_folio(const struct iomap_ops *ops,
                struct iomap_read_folio_ctx *ctx, void *private)
{
        struct folio *folio = ctx->cur_folio;
        struct iomap_iter iter = {
                .inode          = folio->mapping->host,
                .pos            = folio_pos(folio),
                .len            = folio_size(folio),
                .private        = private,
        };
        size_t bytes_submitted = 0;
        int ret;

        trace_iomap_readpage(iter.inode, 1);

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.status = iomap_read_folio_iter(&iter, ctx,
                                &bytes_submitted);

        if (ctx->ops->submit_read)
                ctx->ops->submit_read(ctx);

        if (ctx->cur_folio)
                iomap_read_end(ctx->cur_folio, bytes_submitted);
}
EXPORT_SYMBOL_GPL(iomap_read_folio);

static int iomap_readahead_iter(struct iomap_iter *iter,
                struct iomap_read_folio_ctx *ctx, size_t *cur_bytes_submitted)
{
        int ret;

        while (iomap_length(iter)) {
                if (ctx->cur_folio &&
                    offset_in_folio(ctx->cur_folio, iter->pos) == 0) {
                        iomap_read_end(ctx->cur_folio, *cur_bytes_submitted);
                        ctx->cur_folio = NULL;
                }
                if (!ctx->cur_folio) {
                        ctx->cur_folio = readahead_folio(ctx->rac);
                        if (WARN_ON_ONCE(!ctx->cur_folio))
                                return -EINVAL;
                        *cur_bytes_submitted = 0;
                }
                ret = iomap_read_folio_iter(iter, ctx, cur_bytes_submitted);
                if (ret)
                        return ret;
        }

        return 0;
}

/**
 * iomap_readahead - Attempt to read pages from a file.
 * @ops: The operations vector for the filesystem.
 * @ctx: The ctx used for issuing readahead.
 * @private: The filesystem-specific information for issuing iomap_iter.
 *
 * This function is for filesystems to call to implement their readahead
 * address_space operation.
 *
 * Context: The @ops callbacks may submit I/O (eg to read the addresses of
 * blocks from disc), and may wait for it.  The caller may be trying to
 * access a different page, and so sleeping excessively should be avoided.
 * It may allocate memory, but should avoid costly allocations.  This
 * function is called with memalloc_nofs set, so allocations will not cause
 * the filesystem to be reentered.
 */
void iomap_readahead(const struct iomap_ops *ops,
                struct iomap_read_folio_ctx *ctx, void *private)
{
        struct readahead_control *rac = ctx->rac;
        struct iomap_iter iter = {
                .inode  = rac->mapping->host,
                .pos    = readahead_pos(rac),
                .len    = readahead_length(rac),
                .private = private,
        };
        size_t cur_bytes_submitted;

        trace_iomap_readahead(rac->mapping->host, readahead_count(rac));

        while (iomap_iter(&iter, ops) > 0)
                iter.status = iomap_readahead_iter(&iter, ctx,
                                        &cur_bytes_submitted);

        if (ctx->ops->submit_read)
                ctx->ops->submit_read(ctx);

        if (ctx->cur_folio)
                iomap_read_end(ctx->cur_folio, cur_bytes_submitted);
}
EXPORT_SYMBOL_GPL(iomap_readahead);

/*
 * iomap_is_partially_uptodate checks whether blocks within a folio are
 * uptodate or not.
 *
 * Returns true if all blocks which correspond to the specified part
 * of the folio are uptodate.
 */
bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = folio->mapping->host;
        unsigned first, last;

        if (!ifs)
                return false;

        /* Caller's range may extend past the end of this folio */
        count = min(folio_size(folio) - from, count);

        /* First and last blocks in range within folio */
        first = from >> inode->i_blkbits;
        last = (from + count - 1) >> inode->i_blkbits;

        return ifs_next_nonuptodate_block(folio, first, last) > last;
}
EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);

/**
 * iomap_get_folio - get a folio reference for writing
 * @iter: iteration structure
 * @pos: start offset of write
 * @len: Suggested size of folio to create.
 *
 * Returns a locked reference to the folio at @pos, or an error pointer if the
 * folio could not be obtained.
 */
struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len)
{
        fgf_t fgp = FGP_WRITEBEGIN | FGP_NOFS;

        if (iter->flags & IOMAP_NOWAIT)
                fgp |= FGP_NOWAIT;
        if (iter->flags & IOMAP_DONTCACHE)
                fgp |= FGP_DONTCACHE;
        fgp |= fgf_set_order(len);

        return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
                        fgp, mapping_gfp_mask(iter->inode->i_mapping));
}
EXPORT_SYMBOL_GPL(iomap_get_folio);

bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags)
{
        trace_iomap_release_folio(folio->mapping->host, folio_pos(folio),
                        folio_size(folio));

        /*
         * If the folio is dirty, we refuse to release our metadata because
         * it may be partially dirty.  Once we track per-block dirty state,
         * we can release the metadata if every block is dirty.
         */
        if (folio_test_dirty(folio))
                return false;
        ifs_free(folio);
        return true;
}
EXPORT_SYMBOL_GPL(iomap_release_folio);

void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len)
{
        trace_iomap_invalidate_folio(folio->mapping->host,
                                        folio_pos(folio) + offset, len);

        /*
         * If we're invalidating the entire folio, clear the dirty state
         * from it and release it to avoid unnecessary buildup of the LRU.
         */
        if (offset == 0 && len == folio_size(folio)) {
                WARN_ON_ONCE(folio_test_writeback(folio));
                folio_cancel_dirty(folio);
                ifs_free(folio);
        }
}
EXPORT_SYMBOL_GPL(iomap_invalidate_folio);

bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio)
{
        struct inode *inode = mapping->host;
        size_t len = folio_size(folio);

        ifs_alloc(inode, folio, 0);
        iomap_set_range_dirty(folio, 0, len);
        return filemap_dirty_folio(mapping, folio);
}
EXPORT_SYMBOL_GPL(iomap_dirty_folio);

static void
iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
{
        loff_t i_size = i_size_read(inode);

        /*
         * Only truncate newly allocated pages beyoned EOF, even if the
         * write started inside the existing inode size.
         */
        if (pos + len > i_size)
                truncate_pagecache_range(inode, max(pos, i_size),
                                         pos + len - 1);
}

static int __iomap_write_begin(const struct iomap_iter *iter,
                const struct iomap_write_ops *write_ops, size_t len,
                struct folio *folio)
{
        struct iomap_folio_state *ifs;
        loff_t pos = iter->pos;
        loff_t block_size = i_blocksize(iter->inode);
        loff_t block_start = round_down(pos, block_size);
        loff_t block_end = round_up(pos + len, block_size);
        unsigned int nr_blocks = i_blocks_per_folio(iter->inode, folio);
        size_t from = offset_in_folio(folio, pos), to = from + len;
        size_t poff, plen;

        /*
         * If the write or zeroing completely overlaps the current folio, then
         * entire folio will be dirtied so there is no need for
         * per-block state tracking structures to be attached to this folio.
         * For the unshare case, we must read in the ondisk contents because we
         * are not changing pagecache contents.
         */
        if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) &&
            pos + len >= folio_next_pos(folio))
                return 0;

        ifs = ifs_alloc(iter->inode, folio, iter->flags);
        if ((iter->flags & IOMAP_NOWAIT) && !ifs && nr_blocks > 1)
                return -EAGAIN;

        if (folio_test_uptodate(folio))
                return 0;

        do {
                iomap_adjust_read_range(iter->inode, folio, &block_start,
                                block_end - block_start, &poff, &plen);
                if (plen == 0)
                        break;

                /*
                 * If the read range will be entirely overwritten by the write,
                 * we can skip having to zero/read it in.
                 */
                if (!(iter->flags & IOMAP_UNSHARE) && from <= poff &&
                    to >= poff + plen)
                        continue;

                if (iomap_block_needs_zeroing(iter, block_start)) {
                        if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE))
                                return -EIO;
                        folio_zero_segments(folio, poff, from, to, poff + plen);
                } else {
                        int status;

                        if (iter->flags & IOMAP_NOWAIT)
                                return -EAGAIN;

                        if (write_ops && write_ops->read_folio_range)
                                status = write_ops->read_folio_range(iter,
                                                folio, block_start, plen);
                        else
                                status = iomap_bio_read_folio_range_sync(iter,
                                                folio, block_start, plen);
                        if (status < 0)
                                fserror_report_io(iter->inode,
                                                  FSERR_BUFFERED_READ, pos,
                                                  len, status, GFP_NOFS);
                        if (status)
                                return status;
                }
                iomap_set_range_uptodate(folio, poff, plen);
        } while ((block_start += plen) < block_end);

        return 0;
}

static struct folio *__iomap_get_folio(struct iomap_iter *iter,
                const struct iomap_write_ops *write_ops, size_t len)
{
        loff_t pos = iter->pos;

        if (!mapping_large_folio_support(iter->inode->i_mapping))
                len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));

        if (iter->iomap.flags & IOMAP_F_FOLIO_BATCH) {
                struct folio *folio = folio_batch_next(iter->fbatch);

                if (!folio)
                        return NULL;

                /*
                 * The folio mapping generally shouldn't have changed based on
                 * fs locks, but be consistent with filemap lookup and retry
                 * the iter if it does.
                 */
                folio_lock(folio);
                if (unlikely(folio->mapping != iter->inode->i_mapping)) {
                        iter->iomap.flags |= IOMAP_F_STALE;
                        folio_unlock(folio);
                        return NULL;
                }

                folio_get(folio);
                folio_wait_stable(folio);
                return folio;
        }

        if (write_ops && write_ops->get_folio)
                return write_ops->get_folio(iter, pos, len);
        return iomap_get_folio(iter, pos, len);
}

static void __iomap_put_folio(struct iomap_iter *iter,
                const struct iomap_write_ops *write_ops, size_t ret,
                struct folio *folio)
{
        loff_t pos = iter->pos;

        if (write_ops && write_ops->put_folio) {
                write_ops->put_folio(iter->inode, pos, ret, folio);
        } else {
                folio_unlock(folio);
                folio_put(folio);
        }
}

/* trim pos and bytes to within a given folio */
static loff_t iomap_trim_folio_range(struct iomap_iter *iter,
                struct folio *folio, size_t *offset, u64 *bytes)
{
        loff_t pos = iter->pos;
        size_t fsize = folio_size(folio);

        WARN_ON_ONCE(pos < folio_pos(folio));
        WARN_ON_ONCE(pos >= folio_pos(folio) + fsize);

        *offset = offset_in_folio(folio, pos);
        *bytes = min(*bytes, fsize - *offset);

        return pos;
}

static int iomap_write_begin_inline(const struct iomap_iter *iter,
                struct folio *folio)
{
        /* needs more work for the tailpacking case; disable for now */
        if (WARN_ON_ONCE(iomap_iter_srcmap(iter)->offset != 0))
                return -EIO;
        return iomap_read_inline_data(iter, folio);
}

/*
 * Grab and prepare a folio for write based on iter state. Returns the folio,
 * offset, and length. Callers can optionally pass a max length *plen,
 * otherwise init to zero.
 */
static int iomap_write_begin(struct iomap_iter *iter,
                const struct iomap_write_ops *write_ops, struct folio **foliop,
                size_t *poffset, u64 *plen)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);
        loff_t pos;
        u64 len = min_t(u64, SIZE_MAX, iomap_length(iter));
        struct folio *folio;
        int status = 0;

        len = min_not_zero(len, *plen);
        *foliop = NULL;
        *plen = 0;

        if (fatal_signal_pending(current))
                return -EINTR;

        folio = __iomap_get_folio(iter, write_ops, len);
        if (IS_ERR(folio))
                return PTR_ERR(folio);

        /*
         * No folio means we're done with a batch. We still have range to
         * process so return and let the caller iterate and refill the batch.
         */
        if (!folio) {
                WARN_ON_ONCE(!(iter->iomap.flags & IOMAP_F_FOLIO_BATCH));
                return 0;
        }

        /*
         * Now we have a locked folio, before we do anything with it we need to
         * check that the iomap we have cached is not stale. The inode extent
         * mapping can change due to concurrent IO in flight (e.g.
         * IOMAP_UNWRITTEN state can change and memory reclaim could have
         * reclaimed a previously partially written page at this index after IO
         * completion before this write reaches this file offset) and hence we
         * could do the wrong thing here (zero a page range incorrectly or fail
         * to zero) and corrupt data.
         */
        if (write_ops && write_ops->iomap_valid) {
                bool iomap_valid = write_ops->iomap_valid(iter->inode,
                                                         &iter->iomap);
                if (!iomap_valid) {
                        iter->iomap.flags |= IOMAP_F_STALE;
                        status = 0;
                        goto out_unlock;
                }
        }

        /*
         * The folios in a batch may not be contiguous. If we've skipped
         * forward, advance the iter to the pos of the current folio. If the
         * folio starts beyond the end of the mapping, it may have been trimmed
         * since the lookup for whatever reason. Return a NULL folio to
         * terminate the op.
         */
        if (folio_pos(folio) > iter->pos) {
                len = min_t(u64, folio_pos(folio) - iter->pos,
                                 iomap_length(iter));
                status = iomap_iter_advance(iter, len);
                len = iomap_length(iter);
                if (status || !len)
                        goto out_unlock;
        }

        pos = iomap_trim_folio_range(iter, folio, poffset, &len);

        if (srcmap->type == IOMAP_INLINE)
                status = iomap_write_begin_inline(iter, folio);
        else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
                status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
        else
                status = __iomap_write_begin(iter, write_ops, len, folio);

        if (unlikely(status))
                goto out_unlock;

        *foliop = folio;
        *plen = len;
        return 0;

out_unlock:
        __iomap_put_folio(iter, write_ops, 0, folio);
        return status;
}

static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
                size_t copied, struct folio *folio)
{
        flush_dcache_folio(folio);

        /*
         * The blocks that were entirely written will now be uptodate, so we
         * don't have to worry about a read_folio reading them and overwriting a
         * partial write.  However, if we've encountered a short write and only
         * partially written into a block, it will not be marked uptodate, so a
         * read_folio might come in and destroy our partial write.
         *
         * Do the simplest thing and just treat any short write to a
         * non-uptodate page as a zero-length write, and force the caller to
         * redo the whole thing.
         */
        if (unlikely(copied < len && !folio_test_uptodate(folio)))
                return false;
        iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len);
        iomap_set_range_dirty(folio, offset_in_folio(folio, pos), copied);
        filemap_dirty_folio(inode->i_mapping, folio);
        return true;
}

static bool iomap_write_end_inline(const struct iomap_iter *iter,
                struct folio *folio, loff_t pos, size_t copied)
{
        const struct iomap *iomap = &iter->iomap;
        void *addr;

        WARN_ON_ONCE(!folio_test_uptodate(folio));
        BUG_ON(!iomap_inline_data_valid(iomap));

        if (WARN_ON_ONCE(!iomap->inline_data))
                return false;

        flush_dcache_folio(folio);
        addr = kmap_local_folio(folio, pos);
        memcpy(iomap_inline_data(iomap, pos), addr, copied);
        kunmap_local(addr);

        mark_inode_dirty(iter->inode);
        return true;
}

/*
 * Returns true if all copied bytes have been written to the pagecache,
 * otherwise return false.
 */
static bool iomap_write_end(struct iomap_iter *iter, size_t len, size_t copied,
                struct folio *folio)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);
        loff_t pos = iter->pos;

        if (srcmap->type == IOMAP_INLINE)
                return iomap_write_end_inline(iter, folio, pos, copied);

        if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
                size_t bh_written;

                bh_written = block_write_end(pos, len, copied, folio);
                WARN_ON_ONCE(bh_written != copied && bh_written != 0);
                return bh_written == copied;
        }

        return __iomap_write_end(iter->inode, pos, len, copied, folio);
}

static int iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i,
                const struct iomap_write_ops *write_ops)
{
        ssize_t total_written = 0;
        int status = 0;
        struct address_space *mapping = iter->inode->i_mapping;
        size_t chunk = mapping_max_folio_size(mapping);
        unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0;

        do {
                struct folio *folio;
                loff_t old_size;
                size_t offset;          /* Offset into folio */
                u64 bytes;              /* Bytes to write to folio */
                size_t copied;          /* Bytes copied from user */
                u64 written;            /* Bytes have been written */
                loff_t pos;

                bytes = iov_iter_count(i);
retry:
                offset = iter->pos & (chunk - 1);
                bytes = min(chunk - offset, bytes);
                status = balance_dirty_pages_ratelimited_flags(mapping,
                                                               bdp_flags);
                if (unlikely(status))
                        break;

                if (bytes > iomap_length(iter))
                        bytes = iomap_length(iter);

                /*
                 * Bring in the user page that we'll copy from _first_.
                 * Otherwise there's a nasty deadlock on copying from the
                 * same page as we're writing to, without it being marked
                 * up-to-date.
                 *
                 * For async buffered writes the assumption is that the user
                 * page has already been faulted in. This can be optimized by
                 * faulting the user page.
                 */
                if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
                        status = -EFAULT;
                        break;
                }

                status = iomap_write_begin(iter, write_ops, &folio, &offset,
                                &bytes);
                if (unlikely(status)) {
                        iomap_write_failed(iter->inode, iter->pos, bytes);
                        break;
                }
                if (iter->iomap.flags & IOMAP_F_STALE)
                        break;

                pos = iter->pos;

                if (mapping_writably_mapped(mapping))
                        flush_dcache_folio(folio);

                copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
                written = iomap_write_end(iter, bytes, copied, folio) ?
                          copied : 0;

                /*
                 * Update the in-memory inode size after copying the data into
                 * the page cache.  It's up to the file system to write the
                 * updated size to disk, preferably after I/O completion so that
                 * no stale data is exposed.  Only once that's done can we
                 * unlock and release the folio.
                 */
                old_size = iter->inode->i_size;
                if (pos + written > old_size) {
                        i_size_write(iter->inode, pos + written);
                        iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
                }
                __iomap_put_folio(iter, write_ops, written, folio);

                if (old_size < pos)
                        pagecache_isize_extended(iter->inode, old_size, pos);

                cond_resched();
                if (unlikely(written == 0)) {
                        /*
                         * A short copy made iomap_write_end() reject the
                         * thing entirely.  Might be memory poisoning
                         * halfway through, might be a race with munmap,
                         * might be severe memory pressure.
                         */
                        iomap_write_failed(iter->inode, pos, bytes);
                        iov_iter_revert(i, copied);

                        if (chunk > PAGE_SIZE)
                                chunk /= 2;
                        if (copied) {
                                bytes = copied;
                                goto retry;
                        }
                } else {
                        total_written += written;
                        iomap_iter_advance(iter, written);
                }
        } while (iov_iter_count(i) && iomap_length(iter));

        return total_written ? 0 : status;
}

ssize_t
iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
                const struct iomap_ops *ops,
                const struct iomap_write_ops *write_ops, void *private)
{
        struct iomap_iter iter = {
                .inode          = iocb->ki_filp->f_mapping->host,
                .pos            = iocb->ki_pos,
                .len            = iov_iter_count(i),
                .flags          = IOMAP_WRITE,
                .private        = private,
        };
        ssize_t ret;

        if (iocb->ki_flags & IOCB_NOWAIT)
                iter.flags |= IOMAP_NOWAIT;
        if (iocb->ki_flags & IOCB_DONTCACHE)
                iter.flags |= IOMAP_DONTCACHE;

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.status = iomap_write_iter(&iter, i, write_ops);

        if (unlikely(iter.pos == iocb->ki_pos))
                return ret;
        ret = iter.pos - iocb->ki_pos;
        iocb->ki_pos = iter.pos;
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_file_buffered_write);

static void iomap_write_delalloc_ifs_punch(struct inode *inode,
                struct folio *folio, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        unsigned int first_blk, last_blk;
        loff_t last_byte;
        u8 blkbits = inode->i_blkbits;
        struct iomap_folio_state *ifs;

        /*
         * When we have per-block dirty tracking, there can be
         * blocks within a folio which are marked uptodate
         * but not dirty. In that case it is necessary to punch
         * out such blocks to avoid leaking any delalloc blocks.
         */
        ifs = folio->private;
        if (!ifs)
                return;

        last_byte = min_t(loff_t, end_byte - 1, folio_next_pos(folio) - 1);
        first_blk = offset_in_folio(folio, start_byte) >> blkbits;
        last_blk = offset_in_folio(folio, last_byte) >> blkbits;
        while ((first_blk = ifs_next_clean_block(folio, first_blk, last_blk))
                       <= last_blk) {
                punch(inode, folio_pos(folio) + (first_blk << blkbits),
                                1 << blkbits, iomap);
                first_blk++;
        }
}

static void iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
                loff_t *punch_start_byte, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        if (!folio_test_dirty(folio))
                return;

        /* if dirty, punch up to offset */
        if (start_byte > *punch_start_byte) {
                punch(inode, *punch_start_byte, start_byte - *punch_start_byte,
                                iomap);
        }

        /* Punch non-dirty blocks within folio */
        iomap_write_delalloc_ifs_punch(inode, folio, start_byte, end_byte,
                        iomap, punch);

        /*
         * Make sure the next punch start is correctly bound to
         * the end of this data range, not the end of the folio.
         */
        *punch_start_byte = min_t(loff_t, end_byte, folio_next_pos(folio));
}

/*
 * Scan the data range passed to us for dirty page cache folios. If we find a
 * dirty folio, punch out the preceding range and update the offset from which
 * the next punch will start from.
 *
 * We can punch out storage reservations under clean pages because they either
 * contain data that has been written back - in which case the delalloc punch
 * over that range is a no-op - or they have been read faults in which case they
 * contain zeroes and we can remove the delalloc backing range and any new
 * writes to those pages will do the normal hole filling operation...
 *
 * This makes the logic simple: we only need to keep the delalloc extents only
 * over the dirty ranges of the page cache.
 *
 * This function uses [start_byte, end_byte) intervals (i.e. open ended) to
 * simplify range iterations.
 */
static void iomap_write_delalloc_scan(struct inode *inode,
                loff_t *punch_start_byte, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        while (start_byte < end_byte) {
                struct folio    *folio;

                /* grab locked page */
                folio = filemap_lock_folio(inode->i_mapping,
                                start_byte >> PAGE_SHIFT);
                if (IS_ERR(folio)) {
                        start_byte = ALIGN_DOWN(start_byte, PAGE_SIZE) +
                                        PAGE_SIZE;
                        continue;
                }

                iomap_write_delalloc_punch(inode, folio, punch_start_byte,
                                start_byte, end_byte, iomap, punch);

                /* move offset to start of next folio in range */
                start_byte = folio_next_pos(folio);
                folio_unlock(folio);
                folio_put(folio);
        }
}

/*
 * When a short write occurs, the filesystem might need to use ->iomap_end
 * to remove space reservations created in ->iomap_begin.
 *
 * For filesystems that use delayed allocation, there can be dirty pages over
 * the delalloc extent outside the range of a short write but still within the
 * delalloc extent allocated for this iomap if the write raced with page
 * faults.
 *
 * Punch out all the delalloc blocks in the range given except for those that
 * have dirty data still pending in the page cache - those are going to be
 * written and so must still retain the delalloc backing for writeback.
 *
 * The punch() callback *must* only punch delalloc extents in the range passed
 * to it. It must skip over all other types of extents in the range and leave
 * them completely unchanged. It must do this punch atomically with respect to
 * other extent modifications.
 *
 * The punch() callback may be called with a folio locked to prevent writeback
 * extent allocation racing at the edge of the range we are currently punching.
 * The locked folio may or may not cover the range being punched, so it is not
 * safe for the punch() callback to lock folios itself.
 *
 * Lock order is:
 *
 * inode->i_rwsem (shared or exclusive)
 *   inode->i_mapping->invalidate_lock (exclusive)
 *     folio_lock()
 *       ->punch
 *         internal filesystem allocation lock
 *
 * As we are scanning the page cache for data, we don't need to reimplement the
 * wheel - mapping_seek_hole_data() does exactly what we need to identify the
 * start and end of data ranges correctly even for sub-folio block sizes. This
 * byte range based iteration is especially convenient because it means we
 * don't have to care about variable size folios, nor where the start or end of
 * the data range lies within a folio, if they lie within the same folio or even
 * if there are multiple discontiguous data ranges within the folio.
 *
 * It should be noted that mapping_seek_hole_data() is not aware of EOF, and so
 * can return data ranges that exist in the cache beyond EOF. e.g. a page fault
 * spanning EOF will initialise the post-EOF data to zeroes and mark it up to
 * date. A write page fault can then mark it dirty. If we then fail a write()
 * beyond EOF into that up to date cached range, we allocate a delalloc block
 * beyond EOF and then have to punch it out. Because the range is up to date,
 * mapping_seek_hole_data() will return it, and we will skip the punch because
 * the folio is dirty. THis is incorrect - we always need to punch out delalloc
 * beyond EOF in this case as writeback will never write back and covert that
 * delalloc block beyond EOF. Hence we limit the cached data scan range to EOF,
 * resulting in always punching out the range from the EOF to the end of the
 * range the iomap spans.
 *
 * Intervals are of the form [start_byte, end_byte) (i.e. open ended) because it
 * matches the intervals returned by mapping_seek_hole_data(). i.e. SEEK_DATA
 * returns the start of a data range (start_byte), and SEEK_HOLE(start_byte)
 * returns the end of the data range (data_end). Using closed intervals would
 * require sprinkling this code with magic "+ 1" and "- 1" arithmetic and expose
 * the code to subtle off-by-one bugs....
 */
void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
                loff_t end_byte, unsigned flags, struct iomap *iomap,
                iomap_punch_t punch)
{
        loff_t punch_start_byte = start_byte;
        loff_t scan_end_byte = min(i_size_read(inode), end_byte);

        /*
         * The caller must hold invalidate_lock to avoid races with page faults
         * re-instantiating folios and dirtying them via ->page_mkwrite whilst
         * we walk the cache and perform delalloc extent removal.  Failing to do
         * this can leave dirty pages with no space reservation in the cache.
         */
        lockdep_assert_held_write(&inode->i_mapping->invalidate_lock);

        while (start_byte < scan_end_byte) {
                loff_t          data_end;

                start_byte = mapping_seek_hole_data(inode->i_mapping,
                                start_byte, scan_end_byte, SEEK_DATA);
                /*
                 * If there is no more data to scan, all that is left is to
                 * punch out the remaining range.
                 *
                 * Note that mapping_seek_hole_data is only supposed to return
                 * either an offset or -ENXIO, so WARN on any other error as
                 * that would be an API change without updating the callers.
                 */
                if (start_byte == -ENXIO || start_byte == scan_end_byte)
                        break;
                if (WARN_ON_ONCE(start_byte < 0))
                        return;
                WARN_ON_ONCE(start_byte < punch_start_byte);
                WARN_ON_ONCE(start_byte > scan_end_byte);

                /*
                 * We find the end of this contiguous cached data range by
                 * seeking from start_byte to the beginning of the next hole.
                 */
                data_end = mapping_seek_hole_data(inode->i_mapping, start_byte,
                                scan_end_byte, SEEK_HOLE);
                if (WARN_ON_ONCE(data_end < 0))
                        return;

                /*
                 * If we race with post-direct I/O invalidation of the page cache,
                 * there might be no data left at start_byte.
                 */
                if (data_end == start_byte)
                        continue;

                WARN_ON_ONCE(data_end < start_byte);
                WARN_ON_ONCE(data_end > scan_end_byte);

                iomap_write_delalloc_scan(inode, &punch_start_byte, start_byte,
                                data_end, iomap, punch);

                /* The next data search starts at the end of this one. */
                start_byte = data_end;
        }

        if (punch_start_byte < end_byte)
                punch(inode, punch_start_byte, end_byte - punch_start_byte,
                                iomap);
}
EXPORT_SYMBOL_GPL(iomap_write_delalloc_release);

static int iomap_unshare_iter(struct iomap_iter *iter,
                const struct iomap_write_ops *write_ops)
{
        struct iomap *iomap = &iter->iomap;
        u64 bytes = iomap_length(iter);
        int status;

        if (!iomap_want_unshare_iter(iter))
                return iomap_iter_advance(iter, bytes);

        do {
                struct folio *folio;
                size_t offset;
                bool ret;

                bytes = min_t(u64, SIZE_MAX, bytes);
                status = iomap_write_begin(iter, write_ops, &folio, &offset,
                                &bytes);
                if (unlikely(status))
                        return status;
                if (iomap->flags & IOMAP_F_STALE)
                        break;

                ret = iomap_write_end(iter, bytes, bytes, folio);
                __iomap_put_folio(iter, write_ops, bytes, folio);
                if (WARN_ON_ONCE(!ret))
                        return -EIO;

                cond_resched();

                balance_dirty_pages_ratelimited(iter->inode->i_mapping);

                status = iomap_iter_advance(iter, bytes);
                if (status)
                        break;
        } while ((bytes = iomap_length(iter)) > 0);

        return status;
}

int
iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
                const struct iomap_ops *ops,
                const struct iomap_write_ops *write_ops)
{
        struct iomap_iter iter = {
                .inode          = inode,
                .pos            = pos,
                .flags          = IOMAP_WRITE | IOMAP_UNSHARE,
        };
        loff_t size = i_size_read(inode);
        int ret;

        if (pos < 0 || pos >= size)
                return 0;

        iter.len = min(len, size - pos);
        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.status = iomap_unshare_iter(&iter, write_ops);
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_file_unshare);

/*
 * Flush the remaining range of the iter and mark the current mapping stale.
 * This is used when zero range sees an unwritten mapping that may have had
 * dirty pagecache over it.
 */
static inline int iomap_zero_iter_flush_and_stale(struct iomap_iter *i)
{
        struct address_space *mapping = i->inode->i_mapping;
        loff_t end = i->pos + i->len - 1;

        i->iomap.flags |= IOMAP_F_STALE;
        return filemap_write_and_wait_range(mapping, i->pos, end);
}

static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
                const struct iomap_write_ops *write_ops)
{
        u64 bytes = iomap_length(iter);
        int status;

        do {
                struct folio *folio;
                size_t offset;
                bool ret;

                bytes = min_t(u64, SIZE_MAX, bytes);
                status = iomap_write_begin(iter, write_ops, &folio, &offset,
                                &bytes);
                if (status)
                        return status;
                if (iter->iomap.flags & IOMAP_F_STALE)
                        break;

                /* a NULL folio means we're done with a folio batch */
                if (!folio) {
                        status = iomap_iter_advance_full(iter);
                        break;
                }

                /* warn about zeroing folios beyond eof that won't write back */
                WARN_ON_ONCE(folio_pos(folio) > iter->inode->i_size);

                trace_iomap_zero_iter(iter->inode, folio_pos(folio) + offset,
                                bytes);

                folio_zero_range(folio, offset, bytes);
                folio_mark_accessed(folio);

                ret = iomap_write_end(iter, bytes, bytes, folio);
                __iomap_put_folio(iter, write_ops, bytes, folio);
                if (WARN_ON_ONCE(!ret))
                        return -EIO;

                status = iomap_iter_advance(iter, bytes);
                if (status)
                        break;
        } while ((bytes = iomap_length(iter)) > 0);

        if (did_zero)
                *did_zero = true;
        return status;
}

/**
 * iomap_fill_dirty_folios - fill a folio batch with dirty folios
 * @iter: Iteration structure
 * @start: Start offset of range. Updated based on lookup progress.
 * @end: End offset of range
 * @iomap_flags: Flags to set on the associated iomap to track the batch.
 *
 * Returns the folio count directly. Also returns the associated control flag if
 * the the batch lookup is performed and the expected offset of a subsequent
 * lookup via out params. The caller is responsible to set the flag on the
 * associated iomap.
 */
unsigned int
iomap_fill_dirty_folios(
        struct iomap_iter       *iter,
        loff_t                  *start,
        loff_t                  end,
        unsigned int            *iomap_flags)
{
        struct address_space    *mapping = iter->inode->i_mapping;
        pgoff_t                 pstart = *start >> PAGE_SHIFT;
        pgoff_t                 pend = (end - 1) >> PAGE_SHIFT;
        unsigned int            count;

        if (!iter->fbatch) {
                *start = end;
                return 0;
        }

        count = filemap_get_folios_dirty(mapping, &pstart, pend, iter->fbatch);
        *start = (pstart << PAGE_SHIFT);
        *iomap_flags |= IOMAP_F_FOLIO_BATCH;
        return count;
}
EXPORT_SYMBOL_GPL(iomap_fill_dirty_folios);

int
iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
                const struct iomap_ops *ops,
                const struct iomap_write_ops *write_ops, void *private)
{
        struct folio_batch fbatch;
        struct iomap_iter iter = {
                .inode          = inode,
                .pos            = pos,
                .len            = len,
                .flags          = IOMAP_ZERO,
                .private        = private,
                .fbatch         = &fbatch,
        };
        struct address_space *mapping = inode->i_mapping;
        int ret;
        bool range_dirty;

        folio_batch_init(&fbatch);

        /*
         * To avoid an unconditional flush, check pagecache state and only flush
         * if dirty and the fs returns a mapping that might convert on
         * writeback.
         */
        range_dirty = filemap_range_needs_writeback(mapping, iter.pos,
                                        iter.pos + iter.len - 1);
        while ((ret = iomap_iter(&iter, ops)) > 0) {
                const struct iomap *srcmap = iomap_iter_srcmap(&iter);

                if (WARN_ON_ONCE((iter.iomap.flags & IOMAP_F_FOLIO_BATCH) &&
                                 srcmap->type != IOMAP_UNWRITTEN))
                        return -EIO;

                if (!(iter.iomap.flags & IOMAP_F_FOLIO_BATCH) &&
                    (srcmap->type == IOMAP_HOLE ||
                     srcmap->type == IOMAP_UNWRITTEN)) {
                        s64 status;

                        if (range_dirty) {
                                range_dirty = false;
                                status = iomap_zero_iter_flush_and_stale(&iter);
                        } else {
                                status = iomap_iter_advance_full(&iter);
                        }
                        iter.status = status;
                        continue;
                }

                iter.status = iomap_zero_iter(&iter, did_zero, write_ops);
        }
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_zero_range);

int
iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
                const struct iomap_ops *ops,
                const struct iomap_write_ops *write_ops, void *private)
{
        unsigned int blocksize = i_blocksize(inode);
        unsigned int off = pos & (blocksize - 1);

        /* Block boundary? Nothing to do */
        if (!off)
                return 0;
        return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops,
                        write_ops, private);
}
EXPORT_SYMBOL_GPL(iomap_truncate_page);

static int iomap_folio_mkwrite_iter(struct iomap_iter *iter,
                struct folio *folio)
{
        loff_t length = iomap_length(iter);
        int ret;

        if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
                ret = __block_write_begin_int(folio, iter->pos, length, NULL,
                                              &iter->iomap);
                if (ret)
                        return ret;
                block_commit_write(folio, 0, length);
        } else {
                WARN_ON_ONCE(!folio_test_uptodate(folio));
                folio_mark_dirty(folio);
        }

        return iomap_iter_advance(iter, length);
}

vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops,
                void *private)
{
        struct iomap_iter iter = {
                .inode          = file_inode(vmf->vma->vm_file),
                .flags          = IOMAP_WRITE | IOMAP_FAULT,
                .private        = private,
        };
        struct folio *folio = page_folio(vmf->page);
        ssize_t ret;

        folio_lock(folio);
        ret = folio_mkwrite_check_truncate(folio, iter.inode);
        if (ret < 0)
                goto out_unlock;
        iter.pos = folio_pos(folio);
        iter.len = ret;
        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.status = iomap_folio_mkwrite_iter(&iter, folio);

        if (ret < 0)
                goto out_unlock;
        folio_wait_stable(folio);
        return VM_FAULT_LOCKED;
out_unlock:
        folio_unlock(folio);
        return vmf_fs_error(ret);
}
EXPORT_SYMBOL_GPL(iomap_page_mkwrite);

static void iomap_writeback_init(struct inode *inode, struct folio *folio)
{
        struct iomap_folio_state *ifs = folio->private;

        WARN_ON_ONCE(i_blocks_per_folio(inode, folio) > 1 && !ifs);
        if (ifs) {
                WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending) != 0);
                /*
                 * Set this to the folio size. After processing the folio for
                 * writeback in iomap_writeback_folio(), we'll subtract any
                 * ranges not written back.
                 *
                 * We do this because otherwise, we would have to atomically
                 * increment ifs->write_bytes_pending every time a range in the
                 * folio needs to be written back.
                 */
                atomic_set(&ifs->write_bytes_pending, folio_size(folio));
        }
}

void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
                size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        WARN_ON_ONCE(i_blocks_per_folio(inode, folio) > 1 && !ifs);
        WARN_ON_ONCE(ifs && atomic_read(&ifs->write_bytes_pending) <= 0);

        if (!ifs || atomic_sub_and_test(len, &ifs->write_bytes_pending))
                folio_end_writeback(folio);
}
EXPORT_SYMBOL_GPL(iomap_finish_folio_write);

static int iomap_writeback_range(struct iomap_writepage_ctx *wpc,
                struct folio *folio, u64 pos, u32 rlen, u64 end_pos,
                size_t *bytes_submitted)
{
        do {
                ssize_t ret;

                ret = wpc->ops->writeback_range(wpc, folio, pos, rlen, end_pos);
                if (WARN_ON_ONCE(ret == 0 || ret > rlen))
                        return -EIO;
                if (ret < 0)
                        return ret;
                rlen -= ret;
                pos += ret;

                /*
                 * Holes are not written back by ->writeback_range, so track
                 * if we did handle anything that is not a hole here.
                 */
                if (wpc->iomap.type != IOMAP_HOLE)
                        *bytes_submitted += ret;
        } while (rlen);

        return 0;
}

/*
 * Check interaction of the folio with the file end.
 *
 * If the folio is entirely beyond i_size, return false.  If it straddles
 * i_size, adjust end_pos and zero all data beyond i_size.
 */
static bool iomap_writeback_handle_eof(struct folio *folio, struct inode *inode,
                u64 *end_pos)
{
        u64 isize = i_size_read(inode);

        if (*end_pos > isize) {
                size_t poff = offset_in_folio(folio, isize);
                pgoff_t end_index = isize >> PAGE_SHIFT;

                /*
                 * If the folio is entirely ouside of i_size, skip it.
                 *
                 * This can happen due to a truncate operation that is in
                 * progress and in that case truncate will finish it off once
                 * we've dropped the folio lock.
                 *
                 * Note that the pgoff_t used for end_index is an unsigned long.
                 * If the given offset is greater than 16TB on a 32-bit system,
                 * then if we checked if the folio is fully outside i_size with
                 * "if (folio->index >= end_index + 1)", "end_index + 1" would
                 * overflow and evaluate to 0.  Hence this folio would be
                 * redirtied and written out repeatedly, which would result in
                 * an infinite loop; the user program performing this operation
                 * would hang.  Instead, we can detect this situation by
                 * checking if the folio is totally beyond i_size or if its
                 * offset is just equal to the EOF.
                 */
                if (folio->index > end_index ||
                    (folio->index == end_index && poff == 0))
                        return false;

                /*
                 * The folio straddles i_size.
                 *
                 * It must be zeroed out on each and every writepage invocation
                 * because it may be mmapped:
                 *
                 *    A file is mapped in multiples of the page size.  For a
                 *    file that is not a multiple of the page size, the
                 *    remaining memory is zeroed when mapped, and writes to that
                 *    region are not written out to the file.
                 *
                 * Also adjust the end_pos to the end of file and skip writeback
                 * for all blocks entirely beyond i_size.
                 */
                folio_zero_segment(folio, poff, folio_size(folio));
                *end_pos = isize;
        }

        return true;
}

int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = wpc->inode;
        u64 pos = folio_pos(folio);
        u64 end_pos = pos + folio_size(folio);
        u64 end_aligned = 0;
        loff_t orig_pos = pos;
        size_t bytes_submitted = 0;
        int error = 0;
        u32 rlen;

        WARN_ON_ONCE(!folio_test_locked(folio));
        WARN_ON_ONCE(folio_test_dirty(folio));
        WARN_ON_ONCE(folio_test_writeback(folio));

        trace_iomap_writeback_folio(inode, pos, folio_size(folio));

        if (!iomap_writeback_handle_eof(folio, inode, &end_pos))
                return 0;
        WARN_ON_ONCE(end_pos <= pos);

        if (i_blocks_per_folio(inode, folio) > 1) {
                if (!ifs) {
                        ifs = ifs_alloc(inode, folio, 0);
                        iomap_set_range_dirty(folio, 0, end_pos - pos);
                }

                iomap_writeback_init(inode, folio);
        }

        /*
         * Set the writeback bit ASAP, as the I/O completion for the single
         * block per folio case happen hit as soon as we're submitting the bio.
         */
        folio_start_writeback(folio);

        /*
         * Walk through the folio to find dirty areas to write back.
         */
        end_aligned = round_up(end_pos, i_blocksize(inode));
        while ((rlen = iomap_find_dirty_range(folio, &pos, end_aligned))) {
                error = iomap_writeback_range(wpc, folio, pos, rlen, end_pos,
                                &bytes_submitted);
                if (error)
                        break;
                pos += rlen;
        }

        if (bytes_submitted)
                wpc->nr_folios++;
        if (error && pos > orig_pos)
                fserror_report_io(inode, FSERR_BUFFERED_WRITE, orig_pos, 0,
                                  error, GFP_NOFS);

        /*
         * We can have dirty bits set past end of file in page_mkwrite path
         * while mapping the last partial folio. Hence it's better to clear
         * all the dirty bits in the folio here.
         */
        iomap_clear_range_dirty(folio, 0, folio_size(folio));

        /*
         * Usually the writeback bit is cleared by the I/O completion handler.
         * But we may end up either not actually writing any blocks, or (when
         * there are multiple blocks in a folio) all I/O might have finished
         * already at this point.  In that case we need to clear the writeback
         * bit ourselves right after unlocking the page.
         */
        if (ifs) {
                /*
                 * Subtract any bytes that were initially accounted to
                 * write_bytes_pending but skipped for writeback.
                 */
                size_t bytes_not_submitted = folio_size(folio) -
                                bytes_submitted;

                if (bytes_not_submitted)
                        iomap_finish_folio_write(inode, folio,
                                        bytes_not_submitted);
        } else if (!bytes_submitted) {
                folio_end_writeback(folio);
        }

        mapping_set_error(inode->i_mapping, error);
        return error;
}
EXPORT_SYMBOL_GPL(iomap_writeback_folio);

int
iomap_writepages(struct iomap_writepage_ctx *wpc)
{
        struct address_space *mapping = wpc->inode->i_mapping;
        struct folio *folio = NULL;
        int error;

        /*
         * Writeback from reclaim context should never happen except in the case
         * of a VM regression so warn about it and refuse to write the data.
         */
        if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC | PF_KSWAPD)) ==
                        PF_MEMALLOC))
                return -EIO;

        while ((folio = writeback_iter(mapping, wpc->wbc, folio, &error))) {
                error = iomap_writeback_folio(wpc, folio);
                folio_unlock(folio);
        }

        /*
         * If @error is non-zero, it means that we have a situation where some
         * part of the submission process has failed after we've marked pages
         * for writeback.
         *
         * We cannot cancel the writeback directly in that case, so always call
         * ->writeback_submit to run the I/O completion handler to clear the
         * writeback bit and let the file system proess the errors.
         */
        if (wpc->wb_ctx)
                return wpc->ops->writeback_submit(wpc, error);
        return error;
}
EXPORT_SYMBOL_GPL(iomap_writepages);