// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/falloc.h>
#include <linux/filelock.h>
#include <linux/writeback.h>
#include <linux/compat.h>
#include <linux/slab.h>
#include <linux/btrfs.h>
#include <linux/uio.h>
#include <linux/iversion.h>
#include <linux/fsverity.h>
#include "ctree.h"
#include "direct-io.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "tree-log.h"
#include "locking.h"
#include "qgroup.h"
#include "compression.h"
#include "delalloc-space.h"
#include "reflink.h"
#include "subpage.h"
#include "fs.h"
#include "accessors.h"
#include "extent-tree.h"
#include "file-item.h"
#include "ioctl.h"
#include "file.h"
#include "super.h"
#include "print-tree.h"

/*
 * Unlock folio after btrfs_file_write() is done with it.
 */
static void btrfs_drop_folio(struct btrfs_fs_info *fs_info, struct folio *folio,
                             u64 pos, u64 copied)
{
        u64 block_start = round_down(pos, fs_info->sectorsize);
        u64 block_len = round_up(pos + copied, fs_info->sectorsize) - block_start;

        ASSERT(block_len <= U32_MAX);
        /*
         * Folio checked is some magic around finding folios that have been
         * modified without going through btrfs_dirty_folio().  Clear it here.
         * There should be no need to mark the pages accessed as
         * prepare_one_folio() should have marked them accessed in
         * prepare_one_folio() via find_or_create_page()
         */
        btrfs_folio_clamp_clear_checked(fs_info, folio, block_start, block_len);
        folio_unlock(folio);
        folio_put(folio);
}

/*
 * After copy_folio_from_iter_atomic(), update the following things for delalloc:
 * - Mark newly dirtied folio as DELALLOC in the io tree.
 *   Used to advise which range is to be written back.
 * - Mark modified folio as Uptodate/Dirty and not needing COW fixup
 * - Update inode size for past EOF write
 */
int btrfs_dirty_folio(struct btrfs_inode *inode, struct folio *folio, loff_t pos,
                      size_t write_bytes, struct extent_state **cached, bool noreserve)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        int ret = 0;
        u64 num_bytes;
        u64 start_pos;
        u64 end_of_last_block;
        const u64 end_pos = pos + write_bytes;
        loff_t isize = i_size_read(&inode->vfs_inode);
        unsigned int extra_bits = 0;

        if (write_bytes == 0)
                return 0;

        if (noreserve)
                extra_bits |= EXTENT_NORESERVE;

        start_pos = round_down(pos, fs_info->sectorsize);
        num_bytes = round_up(end_pos - start_pos, fs_info->sectorsize);
        ASSERT(num_bytes <= U32_MAX);
        ASSERT(folio_pos(folio) <= pos && folio_next_pos(folio) >= end_pos);

        end_of_last_block = start_pos + num_bytes - 1;

        /*
         * The pages may have already been dirty, clear out old accounting so
         * we can set things up properly
         */
        btrfs_clear_extent_bit(&inode->io_tree, start_pos, end_of_last_block,
                               EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
                               cached);

        ret = btrfs_set_extent_delalloc(inode, start_pos, end_of_last_block,
                                        extra_bits, cached);
        if (ret)
                return ret;

        btrfs_folio_clamp_set_uptodate(fs_info, folio, start_pos, num_bytes);
        btrfs_folio_clamp_clear_checked(fs_info, folio, start_pos, num_bytes);
        btrfs_folio_clamp_set_dirty(fs_info, folio, start_pos, num_bytes);

        /*
         * we've only changed i_size in ram, and we haven't updated
         * the disk i_size.  There is no need to log the inode
         * at this time.
         */
        if (end_pos > isize)
                i_size_write(&inode->vfs_inode, end_pos);
        return 0;
}

/*
 * this is very complex, but the basic idea is to drop all extents
 * in the range start - end.  hint_block is filled in with a block number
 * that would be a good hint to the block allocator for this file.
 *
 * If an extent intersects the range but is not entirely inside the range
 * it is either truncated or split.  Anything entirely inside the range
 * is deleted from the tree.
 *
 * Note: the VFS' inode number of bytes is not updated, it's up to the caller
 * to deal with that. We set the field 'bytes_found' of the arguments structure
 * with the number of allocated bytes found in the target range, so that the
 * caller can update the inode's number of bytes in an atomic way when
 * replacing extents in a range to avoid races with stat(2).
 */
int btrfs_drop_extents(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct btrfs_inode *inode,
                       struct btrfs_drop_extents_args *args)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 ino = btrfs_ino(inode);
        u64 search_start = args->start;
        u64 disk_bytenr = 0;
        u64 num_bytes = 0;
        u64 extent_offset = 0;
        u64 extent_end = 0;
        u64 last_end = args->start;
        int del_nr = 0;
        int del_slot = 0;
        int extent_type;
        int recow;
        int ret;
        int modify_tree = -1;
        int update_refs;
        int found = 0;
        struct btrfs_path *path = args->path;

        args->bytes_found = 0;
        args->extent_inserted = false;

        /* Must always have a path if ->replace_extent is true */
        ASSERT(!(args->replace_extent && !args->path));

        if (!path) {
                path = btrfs_alloc_path();
                if (!path) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        if (args->drop_cache)
                btrfs_drop_extent_map_range(inode, args->start, args->end - 1, false);

        if (data_race(args->start >= inode->disk_i_size) && !args->replace_extent)
                modify_tree = 0;

        update_refs = (btrfs_root_id(root) != BTRFS_TREE_LOG_OBJECTID);
        while (1) {
                recow = 0;
                ret = btrfs_lookup_file_extent(trans, root, path, ino,
                                               search_start, modify_tree);
                if (ret < 0)
                        break;
                if (ret > 0 && path->slots[0] > 0 && search_start == args->start) {
                        leaf = path->nodes[0];
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
                        if (key.objectid == ino &&
                            key.type == BTRFS_EXTENT_DATA_KEY)
                                path->slots[0]--;
                }
                ret = 0;
next_slot:
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        if (WARN_ON(del_nr > 0)) {
                                btrfs_print_leaf(leaf);
                                ret = -EINVAL;
                                break;
                        }
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                break;
                        if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        leaf = path->nodes[0];
                        recow = 1;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

                if (key.objectid > ino)
                        break;
                if (WARN_ON_ONCE(key.objectid < ino) ||
                    key.type < BTRFS_EXTENT_DATA_KEY) {
                        ASSERT(del_nr == 0);
                        path->slots[0]++;
                        goto next_slot;
                }
                if (key.type > BTRFS_EXTENT_DATA_KEY || key.offset >= args->end)
                        break;

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                extent_type = btrfs_file_extent_type(leaf, fi);

                if (extent_type == BTRFS_FILE_EXTENT_REG ||
                    extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
                        extent_offset = btrfs_file_extent_offset(leaf, fi);
                        extent_end = key.offset +
                                btrfs_file_extent_num_bytes(leaf, fi);
                } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        extent_end = key.offset +
                                btrfs_file_extent_ram_bytes(leaf, fi);
                } else {
                        /* can't happen */
                        BUG();
                }

                /*
                 * Don't skip extent items representing 0 byte lengths. They
                 * used to be created (bug) if while punching holes we hit
                 * -ENOSPC condition. So if we find one here, just ensure we
                 * delete it, otherwise we would insert a new file extent item
                 * with the same key (offset) as that 0 bytes length file
                 * extent item in the call to setup_items_for_insert() later
                 * in this function.
                 */
                if (extent_end == key.offset && extent_end >= search_start) {
                        last_end = extent_end;
                        goto delete_extent_item;
                }

                if (extent_end <= search_start) {
                        path->slots[0]++;
                        goto next_slot;
                }

                found = 1;
                search_start = max(key.offset, args->start);
                if (recow || !modify_tree) {
                        modify_tree = -1;
                        btrfs_release_path(path);
                        continue;
                }

                /*
                 *     | - range to drop - |
                 *  | -------- extent -------- |
                 */
                if (args->start > key.offset && args->end < extent_end) {
                        if (WARN_ON(del_nr > 0)) {
                                btrfs_print_leaf(leaf);
                                ret = -EINVAL;
                                break;
                        }
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = args->start;
                        ret = btrfs_duplicate_item(trans, root, path,
                                                   &new_key);
                        if (ret == -EAGAIN) {
                                btrfs_release_path(path);
                                continue;
                        }
                        if (ret < 0)
                                break;

                        leaf = path->nodes[0];
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        args->start - key.offset);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);

                        extent_offset += args->start - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - args->start);

                        if (update_refs && disk_bytenr > 0) {
                                struct btrfs_ref ref = {
                                        .action = BTRFS_ADD_DELAYED_REF,
                                        .bytenr = disk_bytenr,
                                        .num_bytes = num_bytes,
                                        .parent = 0,
                                        .owning_root = btrfs_root_id(root),
                                        .ref_root = btrfs_root_id(root),
                                };
                                btrfs_init_data_ref(&ref, new_key.objectid,
                                                    args->start - extent_offset,
                                                    0, false);
                                ret = btrfs_inc_extent_ref(trans, &ref);
                                if (unlikely(ret)) {
                                        btrfs_abort_transaction(trans, ret);
                                        break;
                                }
                        }
                        key.offset = args->start;
                }
                /*
                 * From here on out we will have actually dropped something, so
                 * last_end can be updated.
                 */
                last_end = extent_end;

                /*
                 *  | ---- range to drop ----- |
                 *      | -------- extent -------- |
                 */
                if (args->start <= key.offset && args->end < extent_end) {
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        memcpy(&new_key, &key, sizeof(new_key));
                        new_key.offset = args->end;
                        btrfs_set_item_key_safe(trans, path, &new_key);

                        extent_offset += args->end - key.offset;
                        btrfs_set_file_extent_offset(leaf, fi, extent_offset);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - args->end);
                        if (update_refs && disk_bytenr > 0)
                                args->bytes_found += args->end - key.offset;
                        break;
                }

                search_start = extent_end;
                /*
                 *       | ---- range to drop ----- |
                 *  | -------- extent -------- |
                 */
                if (args->start > key.offset && args->end >= extent_end) {
                        if (WARN_ON(del_nr > 0)) {
                                btrfs_print_leaf(leaf);
                                ret = -EINVAL;
                                break;
                        }
                        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                ret = -EOPNOTSUPP;
                                break;
                        }

                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        args->start - key.offset);
                        if (update_refs && disk_bytenr > 0)
                                args->bytes_found += extent_end - args->start;
                        if (args->end == extent_end)
                                break;

                        path->slots[0]++;
                        goto next_slot;
                }

                /*
                 *  | ---- range to drop ----- |
                 *    | ------ extent ------ |
                 */
                if (args->start <= key.offset && args->end >= extent_end) {
delete_extent_item:
                        if (del_nr == 0) {
                                del_slot = path->slots[0];
                                del_nr = 1;
                        } else {
                                if (WARN_ON(del_slot + del_nr != path->slots[0])) {
                                        btrfs_print_leaf(leaf);
                                        ret = -EINVAL;
                                        break;
                                }
                                del_nr++;
                        }

                        if (update_refs &&
                            extent_type == BTRFS_FILE_EXTENT_INLINE) {
                                args->bytes_found += extent_end - key.offset;
                                extent_end = ALIGN(extent_end,
                                                   fs_info->sectorsize);
                        } else if (update_refs && disk_bytenr > 0) {
                                struct btrfs_ref ref = {
                                        .action = BTRFS_DROP_DELAYED_REF,
                                        .bytenr = disk_bytenr,
                                        .num_bytes = num_bytes,
                                        .parent = 0,
                                        .owning_root = btrfs_root_id(root),
                                        .ref_root = btrfs_root_id(root),
                                };
                                btrfs_init_data_ref(&ref, key.objectid,
                                                    key.offset - extent_offset,
                                                    0, false);
                                ret = btrfs_free_extent(trans, &ref);
                                if (unlikely(ret)) {
                                        btrfs_abort_transaction(trans, ret);
                                        break;
                                }
                                args->bytes_found += extent_end - key.offset;
                        }

                        if (args->end == extent_end)
                                break;

                        if (path->slots[0] + 1 < btrfs_header_nritems(leaf)) {
                                path->slots[0]++;
                                goto next_slot;
                        }

                        ret = btrfs_del_items(trans, root, path, del_slot,
                                              del_nr);
                        if (unlikely(ret)) {
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }

                        del_nr = 0;
                        del_slot = 0;

                        btrfs_release_path(path);
                        continue;
                }

                BUG();
        }

        if (!ret && del_nr > 0) {
                /*
                 * Set path->slots[0] to first slot, so that after the delete
                 * if items are move off from our leaf to its immediate left or
                 * right neighbor leafs, we end up with a correct and adjusted
                 * path->slots[0] for our insertion (if args->replace_extent).
                 */
                path->slots[0] = del_slot;
                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (ret)
                        btrfs_abort_transaction(trans, ret);
        }

        leaf = path->nodes[0];
        /*
         * If btrfs_del_items() was called, it might have deleted a leaf, in
         * which case it unlocked our path, so check path->locks[0] matches a
         * write lock.
         */
        if (!ret && args->replace_extent &&
            path->locks[0] == BTRFS_WRITE_LOCK &&
            btrfs_leaf_free_space(leaf) >=
            sizeof(struct btrfs_item) + args->extent_item_size) {

                key.objectid = ino;
                key.type = BTRFS_EXTENT_DATA_KEY;
                key.offset = args->start;
                if (!del_nr && path->slots[0] < btrfs_header_nritems(leaf)) {
                        struct btrfs_key slot_key;

                        btrfs_item_key_to_cpu(leaf, &slot_key, path->slots[0]);
                        if (btrfs_comp_cpu_keys(&key, &slot_key) > 0)
                                path->slots[0]++;
                }
                btrfs_setup_item_for_insert(trans, root, path, &key,
                                            args->extent_item_size);
                args->extent_inserted = true;
        }

        if (!args->path)
                btrfs_free_path(path);
        else if (!args->extent_inserted)
                btrfs_release_path(path);
out:
        args->drop_end = found ? min(args->end, last_end) : args->end;

        return ret;
}

static bool extent_mergeable(struct extent_buffer *leaf, int slot, u64 objectid,
                             u64 bytenr, u64 orig_offset, u64 *start, u64 *end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        u64 extent_end;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return false;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != objectid || key.type != BTRFS_EXTENT_DATA_KEY)
                return false;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG ||
            btrfs_file_extent_disk_bytenr(leaf, fi) != bytenr ||
            btrfs_file_extent_offset(leaf, fi) != key.offset - orig_offset ||
            btrfs_file_extent_compression(leaf, fi) ||
            btrfs_file_extent_encryption(leaf, fi) ||
            btrfs_file_extent_other_encoding(leaf, fi))
                return false;

        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if ((*start && *start != key.offset) || (*end && *end != extent_end))
                return false;

        *start = key.offset;
        *end = extent_end;
        return true;
}

/*
 * Mark extent in the range start - end as written.
 *
 * This changes extent type from 'pre-allocated' to 'regular'. If only
 * part of extent is marked as written, the extent will be split into
 * two or three.
 */
int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
                              struct btrfs_inode *inode, u64 start, u64 end)
{
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_file_extent_item *fi;
        struct btrfs_ref ref = { 0 };
        struct btrfs_key key;
        struct btrfs_key new_key;
        u64 bytenr;
        u64 num_bytes;
        u64 extent_end;
        u64 orig_offset;
        u64 other_start;
        u64 other_end;
        u64 split;
        int del_nr = 0;
        int del_slot = 0;
        int recow;
        int ret;
        u64 ino = btrfs_ino(inode);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
again:
        recow = 0;
        split = start;
        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = split;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0)
                return ret;
        if (ret > 0 && path->slots[0] > 0)
                path->slots[0]--;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (unlikely(key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }
        fi = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);
        if (unlikely(btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_PREALLOC)) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }
        extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
        if (unlikely(key.offset > start || extent_end < end)) {
                ret = -EINVAL;
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
        num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
        orig_offset = key.offset - btrfs_file_extent_offset(leaf, fi);
        memcpy(&new_key, &key, sizeof(new_key));

        if (start == key.offset && end < extent_end) {
                other_start = 0;
                other_end = start;
                if (extent_mergeable(leaf, path->slots[0] - 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        new_key.offset = end;
                        btrfs_set_item_key_safe(trans, path, &new_key);
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        extent_end - end);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     end - orig_offset);
                        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        end - other_start);
                        return 0;
                }
        }

        if (start > key.offset && end == extent_end) {
                other_start = end;
                other_end = 0;
                if (extent_mergeable(leaf, path->slots[0] + 1,
                                     ino, bytenr, orig_offset,
                                     &other_start, &other_end)) {
                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        start - key.offset);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        path->slots[0]++;
                        new_key.offset = start;
                        btrfs_set_item_key_safe(trans, path, &new_key);

                        fi = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_file_extent_item);
                        btrfs_set_file_extent_generation(leaf, fi,
                                                         trans->transid);
                        btrfs_set_file_extent_num_bytes(leaf, fi,
                                                        other_end - start);
                        btrfs_set_file_extent_offset(leaf, fi,
                                                     start - orig_offset);
                        return 0;
                }
        }

        while (start > key.offset || end < extent_end) {
                if (key.offset == start)
                        split = end;

                new_key.offset = split;
                ret = btrfs_duplicate_item(trans, root, path, &new_key);
                if (ret == -EAGAIN) {
                        btrfs_release_path(path);
                        goto again;
                }
                if (unlikely(ret < 0)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }

                leaf = path->nodes[0];
                fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                                    struct btrfs_file_extent_item);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                split - key.offset);

                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);

                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_offset(leaf, fi, split - orig_offset);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - split);

                ref.action = BTRFS_ADD_DELAYED_REF;
                ref.bytenr = bytenr;
                ref.num_bytes = num_bytes;
                ref.parent = 0;
                ref.owning_root = btrfs_root_id(root);
                ref.ref_root = btrfs_root_id(root);
                btrfs_init_data_ref(&ref, ino, orig_offset, 0, false);
                ret = btrfs_inc_extent_ref(trans, &ref);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }

                if (split == start) {
                        key.offset = start;
                } else {
                        if (unlikely(start != key.offset)) {
                                ret = -EINVAL;
                                btrfs_abort_transaction(trans, ret);
                                return ret;
                        }
                        path->slots[0]--;
                        extent_end = end;
                }
                recow = 1;
        }

        other_start = end;
        other_end = 0;

        ref.action = BTRFS_DROP_DELAYED_REF;
        ref.bytenr = bytenr;
        ref.num_bytes = num_bytes;
        ref.parent = 0;
        ref.owning_root = btrfs_root_id(root);
        ref.ref_root = btrfs_root_id(root);
        btrfs_init_data_ref(&ref, ino, orig_offset, 0, false);
        if (extent_mergeable(leaf, path->slots[0] + 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                extent_end = other_end;
                del_slot = path->slots[0] + 1;
                del_nr++;
                ret = btrfs_free_extent(trans, &ref);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
        }
        other_start = 0;
        other_end = start;
        if (extent_mergeable(leaf, path->slots[0] - 1,
                             ino, bytenr, orig_offset,
                             &other_start, &other_end)) {
                if (recow) {
                        btrfs_release_path(path);
                        goto again;
                }
                key.offset = other_start;
                del_slot = path->slots[0];
                del_nr++;
                ret = btrfs_free_extent(trans, &ref);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
        }
        if (del_nr == 0) {
                fi = btrfs_item_ptr(leaf, path->slots[0],
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
        } else {
                fi = btrfs_item_ptr(leaf, del_slot - 1,
                           struct btrfs_file_extent_item);
                btrfs_set_file_extent_type(leaf, fi,
                                           BTRFS_FILE_EXTENT_REG);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                btrfs_set_file_extent_num_bytes(leaf, fi,
                                                extent_end - key.offset);

                ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
                if (unlikely(ret < 0)) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
        }

        return 0;
}

/*
 * On error return an unlocked folio and the error value
 * On success return a locked folio and 0
 */
static int prepare_uptodate_folio(struct inode *inode, struct folio *folio, u64 pos,
                                  u64 len)
{
        u64 clamp_start = max_t(u64, pos, folio_pos(folio));
        u64 clamp_end = min_t(u64, pos + len, folio_next_pos(folio));
        const u32 blocksize = inode_to_fs_info(inode)->sectorsize;
        int ret = 0;

        if (folio_test_uptodate(folio))
                return 0;

        if (IS_ALIGNED(clamp_start, blocksize) &&
            IS_ALIGNED(clamp_end, blocksize))
                return 0;

        ret = btrfs_read_folio(NULL, folio);
        if (ret)
                return ret;
        folio_lock(folio);
        if (unlikely(!folio_test_uptodate(folio))) {
                folio_unlock(folio);
                return -EIO;
        }

        /*
         * Since btrfs_read_folio() will unlock the folio before it returns,
         * there is a window where btrfs_release_folio() can be called to
         * release the page.  Here we check both inode mapping and page
         * private to make sure the page was not released.
         *
         * The private flag check is essential for subpage as we need to store
         * extra bitmap using folio private.
         */
        if (folio->mapping != inode->i_mapping || !folio_test_private(folio)) {
                folio_unlock(folio);
                return -EAGAIN;
        }
        return 0;
}

static gfp_t get_prepare_gfp_flags(struct inode *inode, bool nowait)
{
        gfp_t gfp;

        gfp = btrfs_alloc_write_mask(inode->i_mapping);
        if (nowait) {
                gfp &= ~__GFP_DIRECT_RECLAIM;
                gfp |= GFP_NOWAIT;
        }

        return gfp;
}

/*
 * Get folio into the page cache and lock it.
 */
static noinline int prepare_one_folio(struct inode *inode, struct folio **folio_ret,
                                      loff_t pos, size_t write_bytes,
                                      bool nowait)
{
        const pgoff_t index = pos >> PAGE_SHIFT;
        gfp_t mask = get_prepare_gfp_flags(inode, nowait);
        fgf_t fgp_flags = (nowait ? FGP_WRITEBEGIN | FGP_NOWAIT : FGP_WRITEBEGIN) |
                          fgf_set_order(write_bytes);
        struct folio *folio;
        int ret;

again:
        folio = __filemap_get_folio(inode->i_mapping, index, fgp_flags, mask);
        if (IS_ERR(folio))
                return PTR_ERR(folio);

        ret = set_folio_extent_mapped(folio);
        if (ret < 0) {
                folio_unlock(folio);
                folio_put(folio);
                return ret;
        }
        ret = prepare_uptodate_folio(inode, folio, pos, write_bytes);
        if (ret) {
                /* The folio is already unlocked. */
                folio_put(folio);
                if (!nowait && ret == -EAGAIN)
                        goto again;
                return ret;
        }
        *folio_ret = folio;
        return 0;
}

/*
 * Locks the extent and properly waits for data=ordered extents to finish
 * before allowing the folios to be modified if need.
 *
 * Return:
 * 1 - the extent is locked
 * 0 - the extent is not locked, and everything is OK
 * -EAGAIN - need to prepare the folios again
 */
static noinline int
lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct folio *folio,
                                loff_t pos, size_t write_bytes,
                                u64 *lockstart, u64 *lockend, bool nowait,
                                struct extent_state **cached_state)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        u64 start_pos;
        u64 last_pos;
        int ret = 0;

        start_pos = round_down(pos, fs_info->sectorsize);
        last_pos = round_up(pos + write_bytes, fs_info->sectorsize) - 1;

        if (start_pos < inode->vfs_inode.i_size) {
                struct btrfs_ordered_extent *ordered;

                if (nowait) {
                        if (!btrfs_try_lock_extent(&inode->io_tree, start_pos,
                                                   last_pos, cached_state)) {
                                folio_unlock(folio);
                                folio_put(folio);
                                return -EAGAIN;
                        }
                } else {
                        btrfs_lock_extent(&inode->io_tree, start_pos, last_pos,
                                          cached_state);
                }

                ordered = btrfs_lookup_ordered_range(inode, start_pos,
                                                     last_pos - start_pos + 1);
                if (ordered &&
                    ordered->file_offset + ordered->num_bytes > start_pos &&
                    ordered->file_offset <= last_pos) {
                        btrfs_unlock_extent(&inode->io_tree, start_pos, last_pos,
                                            cached_state);
                        folio_unlock(folio);
                        folio_put(folio);
                        btrfs_start_ordered_extent(ordered);
                        btrfs_put_ordered_extent(ordered);
                        return -EAGAIN;
                }
                if (ordered)
                        btrfs_put_ordered_extent(ordered);

                *lockstart = start_pos;
                *lockend = last_pos;
                ret = 1;
        }

        /*
         * We should be called after prepare_one_folio() which should have locked
         * all pages in the range.
         */
        WARN_ON(!folio_test_locked(folio));

        return ret;
}

/*
 * Check if we can do nocow write into the range [@pos, @pos + @write_bytes)
 *
 * @pos:         File offset.
 * @write_bytes: The length to write, will be updated to the nocow writeable
 *               range.
 * @nowait:      Indicate if we can block or not (non-blocking IO context).
 *
 * This function will flush ordered extents in the range to ensure proper
 * nocow checks.
 *
 * Return:
 * > 0          If we can nocow, and updates @write_bytes.
 *  0           If we can't do a nocow write.
 * -EAGAIN      If we can't do a nocow write because snapshotting of the inode's
 *              root is in progress or because we are in a non-blocking IO
 *              context and need to block (@nowait is true).
 * < 0          If an error happened.
 *
 * NOTE: Callers need to call btrfs_check_nocow_unlock() if we return > 0.
 */
int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
                           size_t *write_bytes, bool nowait)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct btrfs_root *root = inode->root;
        struct extent_state *cached_state = NULL;
        u64 lockstart, lockend;
        u64 cur_offset;
        int ret = 0;

        if (!(inode->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)))
                return 0;

        if (!btrfs_drew_try_write_lock(&root->snapshot_lock))
                return -EAGAIN;

        lockstart = round_down(pos, fs_info->sectorsize);
        lockend = round_up(pos + *write_bytes,
                           fs_info->sectorsize) - 1;

        if (nowait) {
                if (!btrfs_try_lock_ordered_range(inode, lockstart, lockend,
                                                  &cached_state)) {
                        btrfs_drew_write_unlock(&root->snapshot_lock);
                        return -EAGAIN;
                }
        } else {
                btrfs_lock_and_flush_ordered_range(inode, lockstart, lockend,
                                                   &cached_state);
        }

        cur_offset = lockstart;
        while (cur_offset < lockend) {
                u64 num_bytes = lockend - cur_offset + 1;

                ret = can_nocow_extent(inode, cur_offset, &num_bytes, NULL, nowait);
                if (ret <= 0) {
                        /*
                         * If cur_offset == lockstart it means we haven't found
                         * any extent against which we can NOCOW, so unlock the
                         * snapshot lock.
                         */
                        if (cur_offset == lockstart)
                                btrfs_drew_write_unlock(&root->snapshot_lock);
                        break;
                }
                cur_offset += num_bytes;
        }

        btrfs_unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

        /*
         * cur_offset > lockstart means there's at least a partial range we can
         * NOCOW, and that range can cover one or more extents.
         */
        if (cur_offset > lockstart) {
                *write_bytes = min_t(size_t, *write_bytes, cur_offset - pos);
                return 1;
        }

        return ret;
}

void btrfs_check_nocow_unlock(struct btrfs_inode *inode)
{
        btrfs_drew_write_unlock(&inode->root->snapshot_lock);
}

int btrfs_write_check(struct kiocb *iocb, size_t count)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        loff_t pos = iocb->ki_pos;
        int ret;
        loff_t oldsize;

        /*
         * Quickly bail out on NOWAIT writes if we don't have the nodatacow or
         * prealloc flags, as without those flags we always have to COW. We will
         * later check if we can really COW into the target range (using
         * can_nocow_extent() at btrfs_get_blocks_direct_write()).
         */
        if ((iocb->ki_flags & IOCB_NOWAIT) &&
            !(BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)))
                return -EAGAIN;

        ret = file_remove_privs(file);
        if (ret)
                return ret;

        /*
         * We reserve space for updating the inode when we reserve space for the
         * extent we are going to write, so we will enospc out there.  We don't
         * need to start yet another transaction to update the inode as we will
         * update the inode when we finish writing whatever data we write.
         */
        if (!IS_NOCMTIME(inode)) {
                inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
                inode_inc_iversion(inode);
        }

        oldsize = i_size_read(inode);
        if (pos > oldsize) {
                /* Expand hole size to cover write data, preventing empty gap */
                loff_t end_pos = round_up(pos + count, fs_info->sectorsize);

                ret = btrfs_cont_expand(BTRFS_I(inode), oldsize, end_pos);
                if (ret)
                        return ret;
        }

        return 0;
}

static void release_space(struct btrfs_inode *inode, struct extent_changeset *data_reserved,
                          u64 start, u64 len, bool only_release_metadata)
{
        if (len == 0)
                return;

        if (only_release_metadata) {
                btrfs_check_nocow_unlock(inode);
                btrfs_delalloc_release_metadata(inode, len, true);
        } else {
                const struct btrfs_fs_info *fs_info = inode->root->fs_info;

                btrfs_delalloc_release_space(inode, data_reserved,
                                             round_down(start, fs_info->sectorsize),
                                             len, true);
        }
}

/*
 * Reserve data and metadata space for this buffered write range.
 *
 * Return >0 for the number of bytes reserved, which is always block aligned.
 * Return <0 for error.
 */
static ssize_t reserve_space(struct btrfs_inode *inode,
                             struct extent_changeset **data_reserved,
                             u64 start, size_t *len, bool nowait,
                             bool *only_release_metadata)
{
        const struct btrfs_fs_info *fs_info = inode->root->fs_info;
        const unsigned int block_offset = (start & (fs_info->sectorsize - 1));
        size_t reserve_bytes;
        int ret;

        ret = btrfs_check_data_free_space(inode, data_reserved, start, *len, nowait);
        if (ret < 0) {
                int can_nocow;

                if (nowait && (ret == -ENOSPC || ret == -EAGAIN))
                        return -EAGAIN;

                /*
                 * If we don't have to COW at the offset, reserve metadata only.
                 * write_bytes may get smaller than requested here.
                 */
                can_nocow = btrfs_check_nocow_lock(inode, start, len, nowait);
                if (can_nocow < 0)
                        ret = can_nocow;
                if (can_nocow > 0)
                        ret = 0;
                if (ret)
                        return ret;
                *only_release_metadata = true;
        }

        reserve_bytes = round_up(*len + block_offset, fs_info->sectorsize);
        WARN_ON(reserve_bytes == 0);
        ret = btrfs_delalloc_reserve_metadata(inode, reserve_bytes,
                                              reserve_bytes, nowait);
        if (ret) {
                if (!*only_release_metadata)
                        btrfs_free_reserved_data_space(inode, *data_reserved,
                                                       start, *len);
                else
                        btrfs_check_nocow_unlock(inode);

                if (nowait && ret == -ENOSPC)
                        ret = -EAGAIN;
                return ret;
        }
        return reserve_bytes;
}

/* Shrink the reserved data and metadata space from @reserved_len to @new_len. */
static void shrink_reserved_space(struct btrfs_inode *inode,
                                  struct extent_changeset *data_reserved,
                                  u64 reserved_start, u64 reserved_len,
                                  u64 new_len, bool only_release_metadata)
{
        const u64 diff = reserved_len - new_len;

        ASSERT(new_len <= reserved_len);
        btrfs_delalloc_shrink_extents(inode, reserved_len, new_len);
        if (only_release_metadata)
                btrfs_delalloc_release_metadata(inode, diff, true);
        else
                btrfs_delalloc_release_space(inode, data_reserved,
                                             reserved_start + new_len, diff, true);
}

/* Calculate the maximum amount of bytes we can write into one folio. */
static size_t calc_write_bytes(const struct btrfs_inode *inode,
                               const struct iov_iter *iter, u64 start)
{
        const size_t max_folio_size = mapping_max_folio_size(inode->vfs_inode.i_mapping);

        return min(max_folio_size - (start & (max_folio_size - 1)),
                   iov_iter_count(iter));
}

/*
 * Do the heavy-lifting work to copy one range into one folio of the page cache.
 *
 * Return > 0 in case we copied all bytes or just some of them.
 * Return 0 if no bytes were copied, in which case the caller should retry.
 * Return <0 on error.
 */
static int copy_one_range(struct btrfs_inode *inode, struct iov_iter *iter,
                          struct extent_changeset **data_reserved, u64 start,
                          bool nowait)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_state *cached_state = NULL;
        size_t write_bytes = calc_write_bytes(inode, iter, start);
        size_t copied;
        const u64 reserved_start = round_down(start, fs_info->sectorsize);
        u64 reserved_len;
        struct folio *folio = NULL;
        int extents_locked;
        u64 lockstart;
        u64 lockend;
        bool only_release_metadata = false;
        const unsigned int bdp_flags = (nowait ? BDP_ASYNC : 0);
        int ret;

        /*
         * Fault all pages before locking them in prepare_one_folio() to avoid
         * recursive lock.
         */
        if (unlikely(fault_in_iov_iter_readable(iter, write_bytes)))
                return -EFAULT;
        extent_changeset_release(*data_reserved);
        ret = reserve_space(inode, data_reserved, start, &write_bytes, nowait,
                            &only_release_metadata);
        if (ret < 0)
                return ret;
        reserved_len = ret;
        /* Write range must be inside the reserved range. */
        ASSERT(reserved_start <= start);
        ASSERT(start + write_bytes <= reserved_start + reserved_len);

again:
        ret = balance_dirty_pages_ratelimited_flags(inode->vfs_inode.i_mapping,
                                                    bdp_flags);
        if (ret) {
                btrfs_delalloc_release_extents(inode, reserved_len);
                release_space(inode, *data_reserved, reserved_start, reserved_len,
                              only_release_metadata);
                return ret;
        }

        ret = prepare_one_folio(&inode->vfs_inode, &folio, start, write_bytes, false);
        if (ret) {
                btrfs_delalloc_release_extents(inode, reserved_len);
                release_space(inode, *data_reserved, reserved_start, reserved_len,
                              only_release_metadata);
                return ret;
        }

        /*
         * The reserved range goes beyond the current folio, shrink the reserved
         * space to the folio boundary.
         */
        if (reserved_start + reserved_len > folio_next_pos(folio)) {
                const u64 last_block = folio_next_pos(folio);

                shrink_reserved_space(inode, *data_reserved, reserved_start,
                                      reserved_len, last_block - reserved_start,
                                      only_release_metadata);
                write_bytes = last_block - start;
                reserved_len = last_block - reserved_start;
        }

        extents_locked = lock_and_cleanup_extent_if_need(inode, folio, start,
                                                         write_bytes, &lockstart,
                                                         &lockend, nowait,
                                                         &cached_state);
        if (extents_locked < 0) {
                if (!nowait && extents_locked == -EAGAIN)
                        goto again;

                btrfs_delalloc_release_extents(inode, reserved_len);
                release_space(inode, *data_reserved, reserved_start, reserved_len,
                              only_release_metadata);
                return extents_locked;
        }

        copied = copy_folio_from_iter_atomic(folio, offset_in_folio(folio, start),
                                             write_bytes, iter);
        flush_dcache_folio(folio);

        if (unlikely(copied < write_bytes)) {
                u64 last_block;

                /*
                 * The original write range doesn't need an uptodate folio as
                 * the range is block aligned. But now a short copy happened.
                 * We cannot handle it without an uptodate folio.
                 *
                 * So just revert the range and we will retry.
                 */
                if (!folio_test_uptodate(folio)) {
                        iov_iter_revert(iter, copied);
                        copied = 0;
                }

                /* No copied bytes, unlock, release reserved space and exit. */
                if (copied == 0) {
                        if (extents_locked)
                                btrfs_unlock_extent(&inode->io_tree, lockstart, lockend,
                                                    &cached_state);
                        else
                                btrfs_free_extent_state(cached_state);
                        btrfs_delalloc_release_extents(inode, reserved_len);
                        release_space(inode, *data_reserved, reserved_start, reserved_len,
                                      only_release_metadata);
                        btrfs_drop_folio(fs_info, folio, start, copied);
                        return 0;
                }

                /* Release the reserved space beyond the last block. */
                last_block = round_up(start + copied, fs_info->sectorsize);

                shrink_reserved_space(inode, *data_reserved, reserved_start,
                                      reserved_len, last_block - reserved_start,
                                      only_release_metadata);
                reserved_len = last_block - reserved_start;
        }

        ret = btrfs_dirty_folio(inode, folio, start, copied, &cached_state,
                                only_release_metadata);
        /*
         * If we have not locked the extent range, because the range's start
         * offset is >= i_size, we might still have a non-NULL cached extent
         * state, acquired while marking the extent range as delalloc through
         * btrfs_dirty_page(). Therefore free any possible cached extent state
         * to avoid a memory leak.
         */
        if (extents_locked)
                btrfs_unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
        else
                btrfs_free_extent_state(cached_state);

        btrfs_delalloc_release_extents(inode, reserved_len);
        if (ret) {
                btrfs_drop_folio(fs_info, folio, start, copied);
                release_space(inode, *data_reserved, reserved_start, reserved_len,
                              only_release_metadata);
                return ret;
        }
        if (only_release_metadata)
                btrfs_check_nocow_unlock(inode);

        btrfs_drop_folio(fs_info, folio, start, copied);
        return copied;
}

ssize_t btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *iter)
{
        struct file *file = iocb->ki_filp;
        loff_t pos;
        struct inode *inode = file_inode(file);
        struct extent_changeset *data_reserved = NULL;
        size_t num_written = 0;
        ssize_t ret;
        loff_t old_isize;
        unsigned int ilock_flags = 0;
        const bool nowait = (iocb->ki_flags & IOCB_NOWAIT);

        if (nowait)
                ilock_flags |= BTRFS_ILOCK_TRY;

        ret = btrfs_inode_lock(BTRFS_I(inode), ilock_flags);
        if (ret < 0)
                return ret;

        /*
         * We can only trust the isize with inode lock held, or it can race with
         * other buffered writes and cause incorrect call of
         * pagecache_isize_extended() to overwrite existing data.
         */
        old_isize = i_size_read(inode);

        ret = generic_write_checks(iocb, iter);
        if (ret <= 0)
                goto out;

        ret = btrfs_write_check(iocb, ret);
        if (ret < 0)
                goto out;

        pos = iocb->ki_pos;
        while (iov_iter_count(iter) > 0) {
                ret = copy_one_range(BTRFS_I(inode), iter, &data_reserved, pos, nowait);
                if (ret < 0)
                        break;
                pos += ret;
                num_written += ret;
                cond_resched();
        }

        extent_changeset_free(data_reserved);
        if (num_written > 0) {
                pagecache_isize_extended(inode, old_isize, iocb->ki_pos);
                iocb->ki_pos += num_written;
        }
out:
        btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
        return num_written ? num_written : ret;
}

static ssize_t btrfs_encoded_write(struct kiocb *iocb, struct iov_iter *from,
                        const struct btrfs_ioctl_encoded_io_args *encoded)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        loff_t count;
        ssize_t ret;

        btrfs_inode_lock(BTRFS_I(inode), 0);
        count = encoded->len;
        ret = generic_write_checks_count(iocb, &count);
        if (ret == 0 && count != encoded->len) {
                /*
                 * The write got truncated by generic_write_checks_count(). We
                 * can't do a partial encoded write.
                 */
                ret = -EFBIG;
        }
        if (ret || encoded->len == 0)
                goto out;

        ret = btrfs_write_check(iocb, encoded->len);
        if (ret < 0)
                goto out;

        ret = btrfs_do_encoded_write(iocb, from, encoded);
out:
        btrfs_inode_unlock(BTRFS_I(inode), 0);
        return ret;
}

ssize_t btrfs_do_write_iter(struct kiocb *iocb, struct iov_iter *from,
                            const struct btrfs_ioctl_encoded_io_args *encoded)
{
        struct file *file = iocb->ki_filp;
        struct btrfs_inode *inode = BTRFS_I(file_inode(file));
        ssize_t num_written, num_sync;

        if (btrfs_is_shutdown(inode->root->fs_info))
                return -EIO;
        /*
         * If the fs flips readonly due to some impossible error, although we
         * have opened a file as writable, we have to stop this write operation
         * to ensure consistency.
         */
        if (BTRFS_FS_ERROR(inode->root->fs_info))
                return -EROFS;

        if (encoded && (iocb->ki_flags & IOCB_NOWAIT))
                return -EOPNOTSUPP;

        if (encoded) {
                num_written = btrfs_encoded_write(iocb, from, encoded);
                num_sync = encoded->len;
        } else if (iocb->ki_flags & IOCB_DIRECT) {
                num_written = btrfs_direct_write(iocb, from);
                num_sync = num_written;
        } else {
                num_written = btrfs_buffered_write(iocb, from);
                num_sync = num_written;
        }

        btrfs_set_inode_last_sub_trans(inode);

        if (num_sync > 0) {
                num_sync = generic_write_sync(iocb, num_sync);
                if (num_sync < 0)
                        num_written = num_sync;
        }

        return num_written;
}

static ssize_t btrfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        return btrfs_do_write_iter(iocb, from, NULL);
}

int btrfs_release_file(struct inode *inode, struct file *filp)
{
        struct btrfs_file_private *private = filp->private_data;

        if (private) {
                kfree(private->filldir_buf);
                btrfs_free_extent_state(private->llseek_cached_state);
                kfree(private);
                filp->private_data = NULL;
        }

        /*
         * Set by setattr when we are about to truncate a file from a non-zero
         * size to a zero size.  This tries to flush down new bytes that may
         * have been written if the application were using truncate to replace
         * a file in place.
         */
        if (test_and_clear_bit(BTRFS_INODE_FLUSH_ON_CLOSE,
                               &BTRFS_I(inode)->runtime_flags))
                        filemap_flush(inode->i_mapping);
        return 0;
}

static int start_ordered_ops(struct btrfs_inode *inode, loff_t start, loff_t end)
{
        int ret;
        struct blk_plug plug;

        /*
         * This is only called in fsync, which would do synchronous writes, so
         * a plug can merge adjacent IOs as much as possible.  Esp. in case of
         * multiple disks using raid profile, a large IO can be split to
         * several segments of stripe length (currently 64K).
         */
        blk_start_plug(&plug);
        ret = btrfs_fdatawrite_range(inode, start, end);
        blk_finish_plug(&plug);

        return ret;
}

static inline bool skip_inode_logging(const struct btrfs_log_ctx *ctx)
{
        struct btrfs_inode *inode = ctx->inode;
        struct btrfs_fs_info *fs_info = inode->root->fs_info;

        if (btrfs_inode_in_log(inode, btrfs_get_fs_generation(fs_info)) &&
            list_empty(&ctx->ordered_extents))
                return true;

        /*
         * If we are doing a fast fsync we can not bail out if the inode's
         * last_trans is <= then the last committed transaction, because we only
         * update the last_trans of the inode during ordered extent completion,
         * and for a fast fsync we don't wait for that, we only wait for the
         * writeback to complete.
         */
        if (inode->last_trans <= btrfs_get_last_trans_committed(fs_info) &&
            (test_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &inode->runtime_flags) ||
             list_empty(&ctx->ordered_extents)))
                return true;

        return false;
}

/*
 * fsync call for both files and directories.  This logs the inode into
 * the tree log instead of forcing full commits whenever possible.
 *
 * It needs to call filemap_fdatawait so that all ordered extent updates are
 * in the metadata btree are up to date for copying to the log.
 *
 * It drops the inode mutex before doing the tree log commit.  This is an
 * important optimization for directories because holding the mutex prevents
 * new operations on the dir while we write to disk.
 */
int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct dentry *dentry = file_dentry(file);
        struct btrfs_inode *inode = BTRFS_I(d_inode(dentry));
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_trans_handle *trans;
        struct btrfs_log_ctx ctx;
        int ret = 0, err;
        u64 len;
        bool full_sync;
        bool skip_ilock = false;

        if (current->journal_info == BTRFS_TRANS_DIO_WRITE_STUB) {
                skip_ilock = true;
                current->journal_info = NULL;
                btrfs_assert_inode_locked(inode);
        }

        trace_btrfs_sync_file(file, datasync);

        btrfs_init_log_ctx(&ctx, inode);

        /*
         * Always set the range to a full range, otherwise we can get into
         * several problems, from missing file extent items to represent holes
         * when not using the NO_HOLES feature, to log tree corruption due to
         * races between hole detection during logging and completion of ordered
         * extents outside the range, to missing checksums due to ordered extents
         * for which we flushed only a subset of their pages.
         */
        start = 0;
        end = LLONG_MAX;
        len = (u64)LLONG_MAX + 1;

        /*
         * We write the dirty pages in the range and wait until they complete
         * out of the ->i_mutex. If so, we can flush the dirty pages by
         * multi-task, and make the performance up.  See
         * btrfs_wait_ordered_range for an explanation of the ASYNC check.
         */
        ret = start_ordered_ops(inode, start, end);
        if (ret)
                goto out;

        if (skip_ilock)
                down_write(&inode->i_mmap_lock);
        else
                btrfs_inode_lock(inode, BTRFS_ILOCK_MMAP);

        atomic_inc(&root->log_batch);

        /*
         * Before we acquired the inode's lock and the mmap lock, someone may
         * have dirtied more pages in the target range. We need to make sure
         * that writeback for any such pages does not start while we are logging
         * the inode, because if it does, any of the following might happen when
         * we are not doing a full inode sync:
         *
         * 1) We log an extent after its writeback finishes but before its
         *    checksums are added to the csum tree, leading to -EIO errors
         *    when attempting to read the extent after a log replay.
         *
         * 2) We can end up logging an extent before its writeback finishes.
         *    Therefore after the log replay we will have a file extent item
         *    pointing to an unwritten extent (and no data checksums as well).
         *
         * So trigger writeback for any eventual new dirty pages and then we
         * wait for all ordered extents to complete below.
         */
        ret = start_ordered_ops(inode, start, end);
        if (ret) {
                if (skip_ilock)
                        up_write(&inode->i_mmap_lock);
                else
                        btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);
                goto out;
        }

        /*
         * Always check for the full sync flag while holding the inode's lock,
         * to avoid races with other tasks. The flag must be either set all the
         * time during logging or always off all the time while logging.
         * We check the flag here after starting delalloc above, because when
         * running delalloc the full sync flag may be set if we need to drop
         * extra extent map ranges due to temporary memory allocation failures.
         */
        full_sync = test_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &inode->runtime_flags);

        /*
         * We have to do this here to avoid the priority inversion of waiting on
         * IO of a lower priority task while holding a transaction open.
         *
         * For a full fsync we wait for the ordered extents to complete while
         * for a fast fsync we wait just for writeback to complete, and then
         * attach the ordered extents to the transaction so that a transaction
         * commit waits for their completion, to avoid data loss if we fsync,
         * the current transaction commits before the ordered extents complete
         * and a power failure happens right after that.
         *
         * For zoned filesystem, if a write IO uses a ZONE_APPEND command, the
         * logical address recorded in the ordered extent may change. We need
         * to wait for the IO to stabilize the logical address.
         */
        if (full_sync || btrfs_is_zoned(fs_info)) {
                ret = btrfs_wait_ordered_range(inode, start, len);
                clear_bit(BTRFS_INODE_COW_WRITE_ERROR, &inode->runtime_flags);
        } else {
                /*
                 * Get our ordered extents as soon as possible to avoid doing
                 * checksum lookups in the csum tree, and use instead the
                 * checksums attached to the ordered extents.
                 */
                btrfs_get_ordered_extents_for_logging(inode, &ctx.ordered_extents);
                ret = filemap_fdatawait_range(inode->vfs_inode.i_mapping, start, end);
                if (ret)
                        goto out_release_extents;

                /*
                 * Check and clear the BTRFS_INODE_COW_WRITE_ERROR now after
                 * starting and waiting for writeback, because for buffered IO
                 * it may have been set during the end IO callback
                 * (end_bbio_data_write() -> btrfs_finish_ordered_extent()) in
                 * case an error happened and we need to wait for ordered
                 * extents to complete so that any extent maps that point to
                 * unwritten locations are dropped and we don't log them.
                 */
                if (test_and_clear_bit(BTRFS_INODE_COW_WRITE_ERROR, &inode->runtime_flags))
                        ret = btrfs_wait_ordered_range(inode, start, len);
        }

        if (ret)
                goto out_release_extents;

        atomic_inc(&root->log_batch);

        if (skip_inode_logging(&ctx)) {
                /*
                 * We've had everything committed since the last time we were
                 * modified so clear this flag in case it was set for whatever
                 * reason, it's no longer relevant.
                 */
                clear_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &inode->runtime_flags);
                /*
                 * An ordered extent might have started before and completed
                 * already with io errors, in which case the inode was not
                 * updated and we end up here. So check the inode's mapping
                 * for any errors that might have happened since we last
                 * checked called fsync.
                 */
                ret = filemap_check_wb_err(inode->vfs_inode.i_mapping, file->f_wb_err);
                goto out_release_extents;
        }

        btrfs_init_log_ctx_scratch_eb(&ctx);

        /*
         * We use start here because we will need to wait on the IO to complete
         * in btrfs_sync_log, which could require joining a transaction (for
         * example checking cross references in the nocow path).  If we use join
         * here we could get into a situation where we're waiting on IO to
         * happen that is blocked on a transaction trying to commit.  With start
         * we inc the extwriter counter, so we wait for all extwriters to exit
         * before we start blocking joiners.  This comment is to keep somebody
         * from thinking they are super smart and changing this to
         * btrfs_join_transaction *cough*Josef*cough*.
         */
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto out_release_extents;
        }
        trans->in_fsync = true;

        ret = btrfs_log_dentry_safe(trans, dentry, &ctx);
        /*
         * Scratch eb no longer needed, release before syncing log or commit
         * transaction, to avoid holding unnecessary memory during such long
         * operations.
         */
        if (ctx.scratch_eb) {
                free_extent_buffer(ctx.scratch_eb);
                ctx.scratch_eb = NULL;
        }
        btrfs_release_log_ctx_extents(&ctx);
        if (ret < 0) {
                /* Fallthrough and commit/free transaction. */
                ret = BTRFS_LOG_FORCE_COMMIT;
        }

        /* we've logged all the items and now have a consistent
         * version of the file in the log.  It is possible that
         * someone will come in and modify the file, but that's
         * fine because the log is consistent on disk, and we
         * have references to all of the file's extents
         *
         * It is possible that someone will come in and log the
         * file again, but that will end up using the synchronization
         * inside btrfs_sync_log to keep things safe.
         */
        if (skip_ilock)
                up_write(&inode->i_mmap_lock);
        else
                btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);

        if (ret == BTRFS_NO_LOG_SYNC) {
                ret = btrfs_end_transaction(trans);
                goto out;
        }

        /* We successfully logged the inode, attempt to sync the log. */
        if (!ret) {
                ret = btrfs_sync_log(trans, root, &ctx);
                if (!ret) {
                        ret = btrfs_end_transaction(trans);
                        goto out;
                }
        }

        /*
         * At this point we need to commit the transaction because we had
         * btrfs_need_log_full_commit() or some other error.
         *
         * If we didn't do a full sync we have to stop the trans handle, wait on
         * the ordered extents, start it again and commit the transaction.  If
         * we attempt to wait on the ordered extents here we could deadlock with
         * something like fallocate() that is holding the extent lock trying to
         * start a transaction while some other thread is trying to commit the
         * transaction while we (fsync) are currently holding the transaction
         * open.
         */
        if (!full_sync) {
                ret = btrfs_end_transaction(trans);
                if (ret)
                        goto out;
                ret = btrfs_wait_ordered_range(inode, start, len);
                if (ret)
                        goto out;

                /*
                 * This is safe to use here because we're only interested in
                 * making sure the transaction that had the ordered extents is
                 * committed.  We aren't waiting on anything past this point,
                 * we're purely getting the transaction and committing it.
                 */
                trans = btrfs_attach_transaction_barrier(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);

                        /*
                         * We committed the transaction and there's no currently
                         * running transaction, this means everything we care
                         * about made it to disk and we are done.
                         */
                        if (ret == -ENOENT)
                                ret = 0;
                        goto out;
                }
        }

        ret = btrfs_commit_transaction(trans);
out:
        free_extent_buffer(ctx.scratch_eb);
        ASSERT(list_empty(&ctx.list));
        ASSERT(list_empty(&ctx.conflict_inodes));
        err = file_check_and_advance_wb_err(file);
        if (!ret)
                ret = err;
        return ret > 0 ? -EIO : ret;

out_release_extents:
        btrfs_release_log_ctx_extents(&ctx);
        if (skip_ilock)
                up_write(&inode->i_mmap_lock);
        else
                btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);
        goto out;
}

/*
 * btrfs_page_mkwrite() is not allowed to change the file size as it gets
 * called from a page fault handler when a page is first dirtied. Hence we must
 * be careful to check for EOF conditions here. We set the page up correctly
 * for a written page which means we get ENOSPC checking when writing into
 * holes and correct delalloc and unwritten extent mapping on filesystems that
 * support these features.
 *
 * We are not allowed to take the i_mutex here so we have to play games to
 * protect against truncate races as the page could now be beyond EOF.  Because
 * truncate_setsize() writes the inode size before removing pages, once we have
 * the page lock we can determine safely if the page is beyond EOF. If it is not
 * beyond EOF, then the page is guaranteed safe against truncation until we
 * unlock the page.
 */
static vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
{
        struct page *page = vmf->page;
        struct folio *folio = page_folio(page);
        struct btrfs_inode *inode = BTRFS_I(file_inode(vmf->vma->vm_file));
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_io_tree *io_tree = &inode->io_tree;
        struct btrfs_ordered_extent *ordered;
        struct extent_state *cached_state = NULL;
        struct extent_changeset *data_reserved = NULL;
        unsigned long zero_start;
        loff_t size;
        size_t fsize = folio_size(folio);
        int ret;
        bool only_release_metadata = false;
        u64 reserved_space;
        u64 page_start;
        u64 page_end;
        u64 end;

        reserved_space = fsize;

        sb_start_pagefault(inode->vfs_inode.i_sb);
        page_start = folio_pos(folio);
        page_end = page_start + folio_size(folio) - 1;
        end = page_end;

        /*
         * Reserving delalloc space after obtaining the page lock can lead to
         * deadlock. For example, if a dirty page is locked by this function
         * and the call to btrfs_delalloc_reserve_space() ends up triggering
         * dirty page write out, then the btrfs_writepages() function could
         * end up waiting indefinitely to get a lock on the page currently
         * being processed by btrfs_page_mkwrite() function.
         */
        ret = btrfs_check_data_free_space(inode, &data_reserved, page_start,
                                          reserved_space, false);
        if (ret < 0) {
                size_t write_bytes = reserved_space;

                if (btrfs_check_nocow_lock(inode, page_start, &write_bytes, false) <= 0)
                        goto out_noreserve;

                only_release_metadata = true;

                /*
                 * Can't write the whole range, there may be shared extents or
                 * holes in the range, bail out with @only_release_metadata set
                 * to true so that we unlock the nocow lock before returning the
                 * error.
                 */
                if (write_bytes < reserved_space)
                        goto out_noreserve;
        }
        ret = btrfs_delalloc_reserve_metadata(inode, reserved_space,
                                              reserved_space, false);
        if (ret < 0) {
                if (!only_release_metadata)
                        btrfs_free_reserved_data_space(inode, data_reserved,
                                                       page_start, reserved_space);
                goto out_noreserve;
        }

        ret = file_update_time(vmf->vma->vm_file);
        if (ret < 0)
                goto out;
again:
        down_read(&inode->i_mmap_lock);
        folio_lock(folio);
        size = i_size_read(&inode->vfs_inode);

        if ((folio->mapping != inode->vfs_inode.i_mapping) ||
            (page_start >= size)) {
                /* Page got truncated out from underneath us. */
                goto out_unlock;
        }
        folio_wait_writeback(folio);

        btrfs_lock_extent(io_tree, page_start, page_end, &cached_state);
        ret = set_folio_extent_mapped(folio);
        if (ret < 0) {
                btrfs_unlock_extent(io_tree, page_start, page_end, &cached_state);
                goto out_unlock;
        }

        /*
         * We can't set the delalloc bits if there are pending ordered
         * extents.  Drop our locks and wait for them to finish.
         */
        ordered = btrfs_lookup_ordered_range(inode, page_start, fsize);
        if (ordered) {
                btrfs_unlock_extent(io_tree, page_start, page_end, &cached_state);
                folio_unlock(folio);
                up_read(&inode->i_mmap_lock);
                btrfs_start_ordered_extent(ordered);
                btrfs_put_ordered_extent(ordered);
                goto again;
        }

        if (folio_contains(folio, (size - 1) >> PAGE_SHIFT)) {
                reserved_space = round_up(size - page_start, fs_info->sectorsize);
                if (reserved_space < fsize) {
                        const u64 to_free = fsize - reserved_space;

                        end = page_start + reserved_space - 1;
                        if (only_release_metadata)
                                btrfs_delalloc_release_metadata(inode, to_free, true);
                        else
                                btrfs_delalloc_release_space(inode, data_reserved,
                                                             end + 1, to_free, true);
                }
        }

        /*
         * page_mkwrite gets called when the page is firstly dirtied after it's
         * faulted in, but write(2) could also dirty a page and set delalloc
         * bits, thus in this case for space account reason, we still need to
         * clear any delalloc bits within this page range since we have to
         * reserve data&meta space before lock_page() (see above comments).
         */
        btrfs_clear_extent_bit(io_tree, page_start, end,
                               EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
                               EXTENT_DEFRAG, &cached_state);

        ret = btrfs_set_extent_delalloc(inode, page_start, end, 0, &cached_state);
        if (ret < 0) {
                btrfs_unlock_extent(io_tree, page_start, page_end, &cached_state);
                goto out_unlock;
        }

        /* Page is wholly or partially inside EOF. */
        if (page_start + folio_size(folio) > size)
                zero_start = offset_in_folio(folio, size);
        else
                zero_start = fsize;

        if (zero_start != fsize)
                folio_zero_range(folio, zero_start, folio_size(folio) - zero_start);

        btrfs_folio_clear_checked(fs_info, folio, page_start, fsize);
        btrfs_folio_set_dirty(fs_info, folio, page_start, end + 1 - page_start);
        btrfs_folio_set_uptodate(fs_info, folio, page_start, end + 1 - page_start);

        btrfs_set_inode_last_sub_trans(inode);

        if (only_release_metadata)
                btrfs_set_extent_bit(io_tree, page_start, end, EXTENT_NORESERVE,
                                     &cached_state);

        btrfs_unlock_extent(io_tree, page_start, page_end, &cached_state);
        up_read(&inode->i_mmap_lock);

        btrfs_delalloc_release_extents(inode, fsize);
        if (only_release_metadata)
                btrfs_check_nocow_unlock(inode);
        sb_end_pagefault(inode->vfs_inode.i_sb);
        extent_changeset_free(data_reserved);
        return VM_FAULT_LOCKED;

out_unlock:
        folio_unlock(folio);
        up_read(&inode->i_mmap_lock);
out:
        btrfs_delalloc_release_extents(inode, fsize);
        if (only_release_metadata)
                btrfs_delalloc_release_metadata(inode, reserved_space, true);
        else
                btrfs_delalloc_release_space(inode, data_reserved, page_start,
                                             reserved_space, true);
out_noreserve:
        if (only_release_metadata)
                btrfs_check_nocow_unlock(inode);

        sb_end_pagefault(inode->vfs_inode.i_sb);

        extent_changeset_free(data_reserved);

        if (ret < 0)
                return vmf_error(ret);

        /* Make the VM retry the fault. */
        return VM_FAULT_NOPAGE;
}

static const struct vm_operations_struct btrfs_file_vm_ops = {
        .fault          = filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = btrfs_page_mkwrite,
};

static int btrfs_file_mmap_prepare(struct vm_area_desc *desc)
{
        struct file *filp = desc->file;
        struct address_space *mapping = filp->f_mapping;

        if (btrfs_is_shutdown(inode_to_fs_info(file_inode(filp))))
                return -EIO;
        if (!mapping->a_ops->read_folio)
                return -ENOEXEC;

        file_accessed(filp);
        desc->vm_ops = &btrfs_file_vm_ops;

        return 0;
}

static bool hole_mergeable(struct btrfs_inode *inode, struct extent_buffer *leaf,
                           int slot, u64 start, u64 end)
{
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;

        if (slot < 0 || slot >= btrfs_header_nritems(leaf))
                return false;

        btrfs_item_key_to_cpu(leaf, &key, slot);
        if (key.objectid != btrfs_ino(inode) ||
            key.type != BTRFS_EXTENT_DATA_KEY)
                return false;

        fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);

        if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG)
                return false;

        if (btrfs_file_extent_disk_bytenr(leaf, fi))
                return false;

        if (key.offset == end)
                return true;
        if (key.offset + btrfs_file_extent_num_bytes(leaf, fi) == start)
                return true;
        return false;
}

static int fill_holes(struct btrfs_trans_handle *trans,
                struct btrfs_inode *inode,
                struct btrfs_path *path, u64 offset, u64 end)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        struct extent_map *hole_em;
        struct btrfs_key key;
        int ret;

        if (btrfs_fs_incompat(fs_info, NO_HOLES))
                goto out;

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = offset;

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret <= 0) {
                /*
                 * We should have dropped this offset, so if we find it then
                 * something has gone horribly wrong.
                 */
                if (ret == 0)
                        ret = -EINVAL;
                return ret;
        }

        leaf = path->nodes[0];
        if (hole_mergeable(inode, leaf, path->slots[0] - 1, offset, end)) {
                u64 num_bytes;

                path->slots[0]--;
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) +
                        end - offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                goto out;
        }

        if (hole_mergeable(inode, leaf, path->slots[0], offset, end)) {
                u64 num_bytes;

                key.offset = offset;
                btrfs_set_item_key_safe(trans, path, &key);
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end -
                        offset;
                btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
                btrfs_set_file_extent_offset(leaf, fi, 0);
                btrfs_set_file_extent_generation(leaf, fi, trans->transid);
                goto out;
        }
        btrfs_release_path(path);

        ret = btrfs_insert_hole_extent(trans, root, btrfs_ino(inode), offset,
                                       end - offset);
        if (ret)
                return ret;

out:
        btrfs_release_path(path);

        hole_em = btrfs_alloc_extent_map();
        if (!hole_em) {
                btrfs_drop_extent_map_range(inode, offset, end - 1, false);
                btrfs_set_inode_full_sync(inode);
        } else {
                hole_em->start = offset;
                hole_em->len = end - offset;
                hole_em->ram_bytes = hole_em->len;

                hole_em->disk_bytenr = EXTENT_MAP_HOLE;
                hole_em->disk_num_bytes = 0;
                hole_em->generation = trans->transid;

                ret = btrfs_replace_extent_map_range(inode, hole_em, true);
                btrfs_free_extent_map(hole_em);
                if (ret)
                        btrfs_set_inode_full_sync(inode);
        }

        return 0;
}

/*
 * Find a hole extent on given inode and change start/len to the end of hole
 * extent.(hole/vacuum extent whose em->start <= start &&
 *         em->start + em->len > start)
 * When a hole extent is found, return 1 and modify start/len.
 */
static int find_first_non_hole(struct btrfs_inode *inode, u64 *start, u64 *len)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map *em;
        int ret = 0;

        em = btrfs_get_extent(inode, NULL,
                              round_down(*start, fs_info->sectorsize),
                              round_up(*len, fs_info->sectorsize));
        if (IS_ERR(em))
                return PTR_ERR(em);

        /* Hole or vacuum extent(only exists in no-hole mode) */
        if (em->disk_bytenr == EXTENT_MAP_HOLE) {
                const u64 em_end = btrfs_extent_map_end(em);

                ret = 1;
                *len = (em_end > *start + *len) ? 0 : (*start + *len - em_end);
                *start = em_end;
        }
        btrfs_free_extent_map(em);
        return ret;
}

/*
 * Check if there is no folio in the range.
 *
 * We cannot utilize filemap_range_has_page() in a filemap with large folios
 * as we can hit the following false positive:
 *
 *        start                            end
 *        |                                |
 *  |//|//|//|//|  |  |  |  |  |  |  |  |//|//|
 *   \         /                         \   /
 *    Folio A                            Folio B
 *
 * That large folio A and B cover the start and end indexes.
 * In that case filemap_range_has_page() will always return true, but the above
 * case is fine for btrfs_punch_hole_lock_range() usage.
 *
 * So here we only ensure that no other folios is in the range, excluding the
 * head/tail large folio.
 */
static bool check_range_has_page(struct inode *inode, u64 start, u64 end)
{
        struct folio_batch fbatch;
        bool ret = false;
        /*
         * For subpage case, if the range is not at page boundary, we could
         * have pages at the leading/tailing part of the range.
         * This could lead to dead loop since filemap_range_has_page()
         * will always return true.
         * So here we need to do extra page alignment for
         * filemap_range_has_page().
         *
         * And do not decrease page_lockend right now, as it can be 0.
         */
        const u64 page_lockstart = round_up(start, PAGE_SIZE);
        const u64 page_lockend = round_down(end + 1, PAGE_SIZE);
        const pgoff_t start_index = page_lockstart >> PAGE_SHIFT;
        const pgoff_t end_index = (page_lockend - 1) >> PAGE_SHIFT;
        pgoff_t tmp = start_index;
        int found_folios;

        /* The same page or adjacent pages. */
        if (page_lockend <= page_lockstart)
                return false;

        folio_batch_init(&fbatch);
        found_folios = filemap_get_folios(inode->i_mapping, &tmp, end_index, &fbatch);
        for (int i = 0; i < found_folios; i++) {
                struct folio *folio = fbatch.folios[i];

                /* A large folio begins before the start. Not a target. */
                if (folio->index < start_index)
                        continue;
                /* A large folio extends beyond the end. Not a target. */
                if (folio_next_index(folio) > end_index)
                        continue;
                /* A folio doesn't cover the head/tail index. Found a target. */
                ret = true;
                break;
        }
        folio_batch_release(&fbatch);
        return ret;
}

static void btrfs_punch_hole_lock_range(struct inode *inode,
                                        const u64 lockstart, const u64 lockend,
                                        struct extent_state **cached_state)
{
        while (1) {
                truncate_pagecache_range(inode, lockstart, lockend);

                btrfs_lock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                                  cached_state);
                /*
                 * We can't have ordered extents in the range, nor dirty/writeback
                 * pages, because we have locked the inode's VFS lock in exclusive
                 * mode, we have locked the inode's i_mmap_lock in exclusive mode,
                 * we have flushed all delalloc in the range and we have waited
                 * for any ordered extents in the range to complete.
                 * We can race with anyone reading pages from this range, so after
                 * locking the range check if we have pages in the range, and if
                 * we do, unlock the range and retry.
                 */
                if (!check_range_has_page(inode, lockstart, lockend))
                        break;

                btrfs_unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                                    cached_state);
        }

        btrfs_assert_inode_range_clean(BTRFS_I(inode), lockstart, lockend);
}

static int btrfs_insert_replace_extent(struct btrfs_trans_handle *trans,
                                     struct btrfs_inode *inode,
                                     struct btrfs_path *path,
                                     struct btrfs_replace_extent_info *extent_info,
                                     const u64 replace_len,
                                     const u64 bytes_to_drop)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = inode->root;
        struct btrfs_file_extent_item *extent;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        int slot;
        int ret;

        if (replace_len == 0)
                return 0;

        if (extent_info->disk_offset == 0 &&
            btrfs_fs_incompat(fs_info, NO_HOLES)) {
                btrfs_update_inode_bytes(inode, 0, bytes_to_drop);
                return 0;
        }

        key.objectid = btrfs_ino(inode);
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = extent_info->file_offset;
        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                      sizeof(struct btrfs_file_extent_item));
        if (ret)
                return ret;
        leaf = path->nodes[0];
        slot = path->slots[0];
        write_extent_buffer(leaf, extent_info->extent_buf,
                            btrfs_item_ptr_offset(leaf, slot),
                            sizeof(struct btrfs_file_extent_item));
        extent = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
        ASSERT(btrfs_file_extent_type(leaf, extent) != BTRFS_FILE_EXTENT_INLINE);
        btrfs_set_file_extent_offset(leaf, extent, extent_info->data_offset);
        btrfs_set_file_extent_num_bytes(leaf, extent, replace_len);
        if (extent_info->is_new_extent)
                btrfs_set_file_extent_generation(leaf, extent, trans->transid);
        btrfs_release_path(path);

        ret = btrfs_inode_set_file_extent_range(inode, extent_info->file_offset,
                                                replace_len);
        if (ret)
                return ret;

        /* If it's a hole, nothing more needs to be done. */
        if (extent_info->disk_offset == 0) {
                btrfs_update_inode_bytes(inode, 0, bytes_to_drop);
                return 0;
        }

        btrfs_update_inode_bytes(inode, replace_len, bytes_to_drop);

        if (extent_info->is_new_extent && extent_info->insertions == 0) {
                key.objectid = extent_info->disk_offset;
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = extent_info->disk_len;
                ret = btrfs_alloc_reserved_file_extent(trans, root,
                                                       btrfs_ino(inode),
                                                       extent_info->file_offset,
                                                       extent_info->qgroup_reserved,
                                                       &key);
        } else {
                struct btrfs_ref ref = {
                        .action = BTRFS_ADD_DELAYED_REF,
                        .bytenr = extent_info->disk_offset,
                        .num_bytes = extent_info->disk_len,
                        .owning_root = btrfs_root_id(root),
                        .ref_root = btrfs_root_id(root),
                };
                u64 ref_offset;

                ref_offset = extent_info->file_offset - extent_info->data_offset;
                btrfs_init_data_ref(&ref, btrfs_ino(inode), ref_offset, 0, false);
                ret = btrfs_inc_extent_ref(trans, &ref);
        }

        extent_info->insertions++;

        return ret;
}

/*
 * The respective range must have been previously locked, as well as the inode.
 * The end offset is inclusive (last byte of the range).
 * @extent_info is NULL for fallocate's hole punching and non-NULL when replacing
 * the file range with an extent.
 * When not punching a hole, we don't want to end up in a state where we dropped
 * extents without inserting a new one, so we must abort the transaction to avoid
 * a corruption.
 */
int btrfs_replace_file_extents(struct btrfs_inode *inode,
                               struct btrfs_path *path, const u64 start,
                               const u64 end,
                               struct btrfs_replace_extent_info *extent_info,
                               struct btrfs_trans_handle **trans_out)
{
        struct btrfs_drop_extents_args drop_args = { 0 };
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 min_size = btrfs_calc_insert_metadata_size(fs_info, 1);
        u64 ino_size = round_up(inode->vfs_inode.i_size, fs_info->sectorsize);
        struct btrfs_trans_handle *trans = NULL;
        struct btrfs_block_rsv rsv;
        unsigned int rsv_count;
        u64 cur_offset;
        u64 len = end - start;
        int ret = 0;

        if (end <= start)
                return -EINVAL;

        btrfs_init_metadata_block_rsv(fs_info, &rsv, BTRFS_BLOCK_RSV_TEMP);
        rsv.size = btrfs_calc_insert_metadata_size(fs_info, 1);
        rsv.failfast = true;

        /*
         * 1 - update the inode
         * 1 - removing the extents in the range
         * 1 - adding the hole extent if no_holes isn't set or if we are
         *     replacing the range with a new extent
         */
        if (!btrfs_fs_incompat(fs_info, NO_HOLES) || extent_info)
                rsv_count = 3;
        else
                rsv_count = 2;

        trans = btrfs_start_transaction(root, rsv_count);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                trans = NULL;
                goto out_release;
        }

        ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, &rsv,
                                      min_size, false);
        if (WARN_ON(ret))
                goto out_trans;
        trans->block_rsv = &rsv;

        cur_offset = start;
        drop_args.path = path;
        drop_args.end = end + 1;
        drop_args.drop_cache = true;
        while (cur_offset < end) {
                drop_args.start = cur_offset;
                ret = btrfs_drop_extents(trans, root, inode, &drop_args);
                /* If we are punching a hole decrement the inode's byte count */
                if (!extent_info)
                        btrfs_update_inode_bytes(inode, 0,
                                                 drop_args.bytes_found);
                if (ret != -ENOSPC) {
                        /*
                         * The only time we don't want to abort is if we are
                         * attempting to clone a partial inline extent, in which
                         * case we'll get EOPNOTSUPP.  However if we aren't
                         * clone we need to abort no matter what, because if we
                         * got EOPNOTSUPP via prealloc then we messed up and
                         * need to abort.
                         */
                        if (unlikely(ret &&
                                     (ret != -EOPNOTSUPP ||
                                      (extent_info && extent_info->is_new_extent))))
                                btrfs_abort_transaction(trans, ret);
                        break;
                }

                trans->block_rsv = &fs_info->trans_block_rsv;

                if (!extent_info && cur_offset < drop_args.drop_end &&
                    cur_offset < ino_size) {
                        ret = fill_holes(trans, inode, path, cur_offset,
                                         drop_args.drop_end);
                        if (unlikely(ret)) {
                                /*
                                 * If we failed then we didn't insert our hole
                                 * entries for the area we dropped, so now the
                                 * fs is corrupted, so we must abort the
                                 * transaction.
                                 */
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                } else if (!extent_info && cur_offset < drop_args.drop_end) {
                        /*
                         * We are past the i_size here, but since we didn't
                         * insert holes we need to clear the mapped area so we
                         * know to not set disk_i_size in this area until a new
                         * file extent is inserted here.
                         */
                        ret = btrfs_inode_clear_file_extent_range(inode,
                                        cur_offset,
                                        drop_args.drop_end - cur_offset);
                        if (unlikely(ret)) {
                                /*
                                 * We couldn't clear our area, so we could
                                 * presumably adjust up and corrupt the fs, so
                                 * we need to abort.
                                 */
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                }

                if (extent_info &&
                    drop_args.drop_end > extent_info->file_offset) {
                        u64 replace_len = drop_args.drop_end -
                                          extent_info->file_offset;

                        ret = btrfs_insert_replace_extent(trans, inode, path,
                                        extent_info, replace_len,
                                        drop_args.bytes_found);
                        if (unlikely(ret)) {
                                btrfs_abort_transaction(trans, ret);
                                break;
                        }
                        extent_info->data_len -= replace_len;
                        extent_info->data_offset += replace_len;
                        extent_info->file_offset += replace_len;
                }

                /*
                 * We are releasing our handle on the transaction, balance the
                 * dirty pages of the btree inode and flush delayed items, and
                 * then get a new transaction handle, which may now point to a
                 * new transaction in case someone else may have committed the
                 * transaction we used to replace/drop file extent items. So
                 * bump the inode's iversion and update mtime and ctime except
                 * if we are called from a dedupe context. This is because a
                 * power failure/crash may happen after the transaction is
                 * committed and before we finish replacing/dropping all the
                 * file extent items we need.
                 */
                inode_inc_iversion(&inode->vfs_inode);

                if (!extent_info || extent_info->update_times)
                        inode_set_mtime_to_ts(&inode->vfs_inode,
                                              inode_set_ctime_current(&inode->vfs_inode));

                ret = btrfs_update_inode(trans, inode);
                if (ret)
                        break;

                btrfs_end_transaction(trans);
                btrfs_btree_balance_dirty(fs_info);

                trans = btrfs_start_transaction(root, rsv_count);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        trans = NULL;
                        break;
                }

                ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
                                              &rsv, min_size, false);
                if (WARN_ON(ret))
                        break;
                trans->block_rsv = &rsv;

                cur_offset = drop_args.drop_end;
                len = end - cur_offset;
                if (!extent_info && len) {
                        ret = find_first_non_hole(inode, &cur_offset, &len);
                        if (unlikely(ret < 0))
                                break;
                        if (ret && !len) {
                                ret = 0;
                                break;
                        }
                }
        }

        /*
         * If we were cloning, force the next fsync to be a full one since we
         * we replaced (or just dropped in the case of cloning holes when
         * NO_HOLES is enabled) file extent items and did not setup new extent
         * maps for the replacement extents (or holes).
         */
        if (extent_info && !extent_info->is_new_extent)
                btrfs_set_inode_full_sync(inode);

        if (ret)
                goto out_trans;

        trans->block_rsv = &fs_info->trans_block_rsv;
        /*
         * If we are using the NO_HOLES feature we might have had already an
         * hole that overlaps a part of the region [lockstart, lockend] and
         * ends at (or beyond) lockend. Since we have no file extent items to
         * represent holes, drop_end can be less than lockend and so we must
         * make sure we have an extent map representing the existing hole (the
         * call to __btrfs_drop_extents() might have dropped the existing extent
         * map representing the existing hole), otherwise the fast fsync path
         * will not record the existence of the hole region
         * [existing_hole_start, lockend].
         */
        if (drop_args.drop_end <= end)
                drop_args.drop_end = end + 1;
        /*
         * Don't insert file hole extent item if it's for a range beyond eof
         * (because it's useless) or if it represents a 0 bytes range (when
         * cur_offset == drop_end).
         */
        if (!extent_info && cur_offset < ino_size &&
            cur_offset < drop_args.drop_end) {
                ret = fill_holes(trans, inode, path, cur_offset,
                                 drop_args.drop_end);
                if (unlikely(ret)) {
                        /* Same comment as above. */
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }
        } else if (!extent_info && cur_offset < drop_args.drop_end) {
                /* See the comment in the loop above for the reasoning here. */
                ret = btrfs_inode_clear_file_extent_range(inode, cur_offset,
                                        drop_args.drop_end - cur_offset);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }

        }
        if (extent_info) {
                ret = btrfs_insert_replace_extent(trans, inode, path,
                                extent_info, extent_info->data_len,
                                drop_args.bytes_found);
                if (unlikely(ret)) {
                        btrfs_abort_transaction(trans, ret);
                        goto out_trans;
                }
        }

out_trans:
        if (!trans)
                goto out_release;

        trans->block_rsv = &fs_info->trans_block_rsv;
        if (ret)
                btrfs_end_transaction(trans);
        else
                *trans_out = trans;
out_release:
        btrfs_block_rsv_release(fs_info, &rsv, (u64)-1, NULL);
        return ret;
}

static int btrfs_punch_hole(struct file *file, loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_state *cached_state = NULL;
        struct btrfs_path *path;
        struct btrfs_trans_handle *trans = NULL;
        u64 lockstart;
        u64 lockend;
        u64 tail_start;
        u64 tail_len;
        const u64 orig_start = offset;
        const u64 orig_end = offset + len - 1;
        int ret = 0;
        bool same_block;
        u64 ino_size;
        bool truncated_block = false;
        bool updated_inode = false;

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        ret = btrfs_wait_ordered_range(BTRFS_I(inode), offset, len);
        if (ret)
                goto out_only_mutex;

        ino_size = round_up(inode->i_size, fs_info->sectorsize);
        ret = find_first_non_hole(BTRFS_I(inode), &offset, &len);
        if (ret < 0)
                goto out_only_mutex;
        if (ret && !len) {
                /* Already in a large hole */
                ret = 0;
                goto out_only_mutex;
        }

        ret = file_modified(file);
        if (ret)
                goto out_only_mutex;

        lockstart = round_up(offset, fs_info->sectorsize);
        lockend = round_down(offset + len, fs_info->sectorsize) - 1;
        same_block = (BTRFS_BYTES_TO_BLKS(fs_info, offset))
                == (BTRFS_BYTES_TO_BLKS(fs_info, offset + len - 1));
        /*
         * Only do this if we are in the same block and we aren't doing the
         * entire block.
         */
        if (same_block && len < fs_info->sectorsize) {
                if (offset < ino_size) {
                        truncated_block = true;
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset + len - 1,
                                                   orig_start, orig_end);
                } else {
                        ret = 0;
                }
                goto out_only_mutex;
        }

        /* zero back part of the first block */
        if (offset < ino_size) {
                truncated_block = true;
                ret = btrfs_truncate_block(BTRFS_I(inode), offset, orig_start, orig_end);
                if (ret) {
                        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
                        return ret;
                }
        }

        /* Check the aligned pages after the first unaligned page,
         * if offset != orig_start, which means the first unaligned page
         * including several following pages are already in holes,
         * the extra check can be skipped */
        if (offset == orig_start) {
                /* after truncate page, check hole again */
                len = offset + len - lockstart;
                offset = lockstart;
                ret = find_first_non_hole(BTRFS_I(inode), &offset, &len);
                if (ret < 0)
                        goto out_only_mutex;
                if (ret && !len) {
                        ret = 0;
                        goto out_only_mutex;
                }
                lockstart = offset;
        }

        /* Check the tail unaligned part is in a hole */
        tail_start = lockend + 1;
        tail_len = offset + len - tail_start;
        if (tail_len) {
                ret = find_first_non_hole(BTRFS_I(inode), &tail_start, &tail_len);
                if (unlikely(ret < 0))
                        goto out_only_mutex;
                if (!ret) {
                        /* zero the front end of the last page */
                        if (tail_start + tail_len < ino_size) {
                                truncated_block = true;
                                ret = btrfs_truncate_block(BTRFS_I(inode),
                                                        tail_start + tail_len - 1,
                                                        orig_start, orig_end);
                                if (ret)
                                        goto out_only_mutex;
                        }
                }
        }

        if (lockend < lockstart) {
                ret = 0;
                goto out_only_mutex;
        }

        btrfs_punch_hole_lock_range(inode, lockstart, lockend, &cached_state);

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        ret = btrfs_replace_file_extents(BTRFS_I(inode), path, lockstart,
                                         lockend, NULL, &trans);
        btrfs_free_path(path);
        if (ret)
                goto out;

        ASSERT(trans != NULL);
        inode_inc_iversion(inode);
        inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
        ret = btrfs_update_inode(trans, BTRFS_I(inode));
        updated_inode = true;
        btrfs_end_transaction(trans);
        btrfs_btree_balance_dirty(fs_info);
out:
        btrfs_unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                            &cached_state);
out_only_mutex:
        if (!updated_inode && truncated_block && !ret) {
                /*
                 * If we only end up zeroing part of a page, we still need to
                 * update the inode item, so that all the time fields are
                 * updated as well as the necessary btrfs inode in memory fields
                 * for detecting, at fsync time, if the inode isn't yet in the
                 * log tree or it's there but not up to date.
                 */
                struct timespec64 now = inode_set_ctime_current(inode);

                inode_inc_iversion(inode);
                inode_set_mtime_to_ts(inode, now);
                trans = btrfs_start_transaction(root, 1);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                } else {
                        int ret2;

                        ret = btrfs_update_inode(trans, BTRFS_I(inode));
                        ret2 = btrfs_end_transaction(trans);
                        if (!ret)
                                ret = ret2;
                }
        }
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
        return ret;
}

/* Helper structure to record which range is already reserved */
struct falloc_range {
        struct list_head list;
        u64 start;
        u64 len;
};

/*
 * Helper function to add falloc range
 *
 * Caller should have locked the larger range of extent containing
 * [start, len)
 */
static int add_falloc_range(struct list_head *head, u64 start, u64 len)
{
        struct falloc_range *range = NULL;

        if (!list_empty(head)) {
                /*
                 * As fallocate iterates by bytenr order, we only need to check
                 * the last range.
                 */
                range = list_last_entry(head, struct falloc_range, list);
                if (range->start + range->len == start) {
                        range->len += len;
                        return 0;
                }
        }

        range = kmalloc_obj(*range);
        if (!range)
                return -ENOMEM;
        range->start = start;
        range->len = len;
        list_add_tail(&range->list, head);
        return 0;
}

static int btrfs_fallocate_update_isize(struct inode *inode,
                                        const u64 end,
                                        const int mode)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 range_start;
        u64 range_end;
        int ret;
        int ret2;

        if (mode & FALLOC_FL_KEEP_SIZE || end <= i_size_read(inode))
                return 0;

        range_start = round_down(i_size_read(inode), root->fs_info->sectorsize);
        range_end = round_up(end, root->fs_info->sectorsize);

        ret = btrfs_inode_set_file_extent_range(BTRFS_I(inode), range_start,
                                                range_end - range_start);
        if (ret)
                return ret;

        trans = btrfs_start_transaction(root, 1);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        inode_set_ctime_current(inode);
        i_size_write(inode, end);
        btrfs_inode_safe_disk_i_size_write(BTRFS_I(inode), 0);
        ret = btrfs_update_inode(trans, BTRFS_I(inode));
        ret2 = btrfs_end_transaction(trans);

        return ret ? ret : ret2;
}

enum {
        RANGE_BOUNDARY_WRITTEN_EXTENT,
        RANGE_BOUNDARY_PREALLOC_EXTENT,
        RANGE_BOUNDARY_HOLE,
};

static int btrfs_zero_range_check_range_boundary(struct btrfs_inode *inode,
                                                 u64 offset)
{
        const u64 sectorsize = inode->root->fs_info->sectorsize;
        struct extent_map *em;
        int ret;

        offset = round_down(offset, sectorsize);
        em = btrfs_get_extent(inode, NULL, offset, sectorsize);
        if (IS_ERR(em))
                return PTR_ERR(em);

        if (em->disk_bytenr == EXTENT_MAP_HOLE)
                ret = RANGE_BOUNDARY_HOLE;
        else if (em->flags & EXTENT_FLAG_PREALLOC)
                ret = RANGE_BOUNDARY_PREALLOC_EXTENT;
        else
                ret = RANGE_BOUNDARY_WRITTEN_EXTENT;

        btrfs_free_extent_map(em);
        return ret;
}

static int btrfs_zero_range(struct inode *inode,
                            loff_t offset,
                            loff_t len,
                            const int mode)
{
        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
        struct extent_map *em;
        struct extent_changeset *data_reserved = NULL;
        int ret;
        u64 alloc_hint = 0;
        const u64 sectorsize = fs_info->sectorsize;
        const u64 orig_start = offset;
        const u64 orig_end = offset + len - 1;
        u64 alloc_start = round_down(offset, sectorsize);
        u64 alloc_end = round_up(offset + len, sectorsize);
        u64 bytes_to_reserve = 0;
        bool space_reserved = false;

        em = btrfs_get_extent(BTRFS_I(inode), NULL, alloc_start,
                              alloc_end - alloc_start);
        if (IS_ERR(em)) {
                ret = PTR_ERR(em);
                goto out;
        }

        /*
         * Avoid hole punching and extent allocation for some cases. More cases
         * could be considered, but these are unlikely common and we keep things
         * as simple as possible for now. Also, intentionally, if the target
         * range contains one or more prealloc extents together with regular
         * extents and holes, we drop all the existing extents and allocate a
         * new prealloc extent, so that we get a larger contiguous disk extent.
         */
        if (em->start <= alloc_start && (em->flags & EXTENT_FLAG_PREALLOC)) {
                const u64 em_end = btrfs_extent_map_end(em);

                if (em_end >= offset + len) {
                        /*
                         * The whole range is already a prealloc extent,
                         * do nothing except updating the inode's i_size if
                         * needed.
                         */
                        btrfs_free_extent_map(em);
                        ret = btrfs_fallocate_update_isize(inode, offset + len,
                                                           mode);
                        goto out;
                }
                /*
                 * Part of the range is already a prealloc extent, so operate
                 * only on the remaining part of the range.
                 */
                alloc_start = em_end;
                ASSERT(IS_ALIGNED(alloc_start, sectorsize));
                len = offset + len - alloc_start;
                offset = alloc_start;
                alloc_hint = btrfs_extent_map_block_start(em) + em->len;
        }
        btrfs_free_extent_map(em);

        if (BTRFS_BYTES_TO_BLKS(fs_info, offset) ==
            BTRFS_BYTES_TO_BLKS(fs_info, offset + len - 1)) {
                em = btrfs_get_extent(BTRFS_I(inode), NULL, alloc_start, sectorsize);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        goto out;
                }

                if (em->flags & EXTENT_FLAG_PREALLOC) {
                        btrfs_free_extent_map(em);
                        ret = btrfs_fallocate_update_isize(inode, offset + len,
                                                           mode);
                        goto out;
                }
                if (len < sectorsize && em->disk_bytenr != EXTENT_MAP_HOLE) {
                        btrfs_free_extent_map(em);
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset + len - 1,
                                                   orig_start, orig_end);
                        if (!ret)
                                ret = btrfs_fallocate_update_isize(inode,
                                                                   offset + len,
                                                                   mode);
                        return ret;
                }
                btrfs_free_extent_map(em);
                alloc_start = round_down(offset, sectorsize);
                alloc_end = alloc_start + sectorsize;
                goto reserve_space;
        }

        alloc_start = round_up(offset, sectorsize);
        alloc_end = round_down(offset + len, sectorsize);

        /*
         * For unaligned ranges, check the pages at the boundaries, they might
         * map to an extent, in which case we need to partially zero them, or
         * they might map to a hole, in which case we need our allocation range
         * to cover them.
         */
        if (!IS_ALIGNED(offset, sectorsize)) {
                ret = btrfs_zero_range_check_range_boundary(BTRFS_I(inode),
                                                            offset);
                if (ret < 0)
                        goto out;
                if (ret == RANGE_BOUNDARY_HOLE) {
                        alloc_start = round_down(offset, sectorsize);
                        ret = 0;
                } else if (ret == RANGE_BOUNDARY_WRITTEN_EXTENT) {
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset,
                                                   orig_start, orig_end);
                        if (ret)
                                goto out;
                } else {
                        ret = 0;
                }
        }

        if (!IS_ALIGNED(offset + len, sectorsize)) {
                ret = btrfs_zero_range_check_range_boundary(BTRFS_I(inode),
                                                            offset + len);
                if (ret < 0)
                        goto out;
                if (ret == RANGE_BOUNDARY_HOLE) {
                        alloc_end = round_up(offset + len, sectorsize);
                        ret = 0;
                } else if (ret == RANGE_BOUNDARY_WRITTEN_EXTENT) {
                        ret = btrfs_truncate_block(BTRFS_I(inode), offset + len - 1,
                                                   orig_start, orig_end);
                        if (ret)
                                goto out;
                } else {
                        ret = 0;
                }
        }

reserve_space:
        if (alloc_start < alloc_end) {
                struct extent_state *cached_state = NULL;
                const u64 lockstart = alloc_start;
                const u64 lockend = alloc_end - 1;

                bytes_to_reserve = alloc_end - alloc_start;
                ret = btrfs_alloc_data_chunk_ondemand(BTRFS_I(inode),
                                                      bytes_to_reserve);
                if (ret < 0)
                        goto out;
                space_reserved = true;
                btrfs_punch_hole_lock_range(inode, lockstart, lockend,
                                            &cached_state);
                ret = btrfs_qgroup_reserve_data(BTRFS_I(inode), &data_reserved,
                                                alloc_start, bytes_to_reserve);
                if (ret) {
                        btrfs_unlock_extent(&BTRFS_I(inode)->io_tree, lockstart,
                                            lockend, &cached_state);
                        goto out;
                }
                ret = btrfs_prealloc_file_range(inode, mode, alloc_start,
                                                alloc_end - alloc_start,
                                                fs_info->sectorsize,
                                                offset + len, &alloc_hint);
                btrfs_unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                                    &cached_state);
                /* btrfs_prealloc_file_range releases reserved space on error */
                if (ret) {
                        space_reserved = false;
                        goto out;
                }
        }
        ret = btrfs_fallocate_update_isize(inode, offset + len, mode);
 out:
        if (ret && space_reserved)
                btrfs_free_reserved_data_space(BTRFS_I(inode), data_reserved,
                                               alloc_start, bytes_to_reserve);
        extent_changeset_free(data_reserved);

        return ret;
}

static long btrfs_fallocate(struct file *file, int mode,
                            loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct extent_state *cached_state = NULL;
        struct extent_changeset *data_reserved = NULL;
        struct falloc_range *range;
        struct falloc_range *tmp;
        LIST_HEAD(reserve_list);
        u64 cur_offset;
        u64 last_byte;
        u64 alloc_start;
        u64 alloc_end;
        u64 alloc_hint = 0;
        u64 locked_end;
        u64 actual_end = 0;
        u64 data_space_needed = 0;
        u64 data_space_reserved = 0;
        u64 qgroup_reserved = 0;
        struct extent_map *em;
        int blocksize = BTRFS_I(inode)->root->fs_info->sectorsize;
        int ret;

        if (btrfs_is_shutdown(inode_to_fs_info(inode)))
                return -EIO;

        /* Do not allow fallocate in ZONED mode */
        if (btrfs_is_zoned(inode_to_fs_info(inode)))
                return -EOPNOTSUPP;

        alloc_start = round_down(offset, blocksize);
        alloc_end = round_up(offset + len, blocksize);
        cur_offset = alloc_start;

        /* Make sure we aren't being give some crap mode */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
                     FALLOC_FL_ZERO_RANGE))
                return -EOPNOTSUPP;

        if (mode & FALLOC_FL_PUNCH_HOLE)
                return btrfs_punch_hole(file, offset, len);

        btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) {
                ret = inode_newsize_ok(inode, offset + len);
                if (ret)
                        goto out;
        }

        ret = file_modified(file);
        if (ret)
                goto out;

        /*
         * TODO: Move these two operations after we have checked
         * accurate reserved space, or fallocate can still fail but
         * with page truncated or size expanded.
         *
         * But that's a minor problem and won't do much harm BTW.
         */
        if (alloc_start > inode->i_size) {
                ret = btrfs_cont_expand(BTRFS_I(inode), i_size_read(inode),
                                        alloc_start);
                if (ret)
                        goto out;
        } else if (offset + len > inode->i_size) {
                /*
                 * If we are fallocating from the end of the file onward we
                 * need to zero out the end of the block if i_size lands in the
                 * middle of a block.
                 */
                ret = btrfs_truncate_block(BTRFS_I(inode), inode->i_size,
                                           inode->i_size, (u64)-1);
                if (ret)
                        goto out;
        }

        /*
         * We have locked the inode at the VFS level (in exclusive mode) and we
         * have locked the i_mmap_lock lock (in exclusive mode). Now before
         * locking the file range, flush all dealloc in the range and wait for
         * all ordered extents in the range to complete. After this we can lock
         * the file range and, due to the previous locking we did, we know there
         * can't be more delalloc or ordered extents in the range.
         */
        ret = btrfs_wait_ordered_range(BTRFS_I(inode), alloc_start,
                                       alloc_end - alloc_start);
        if (ret)
                goto out;

        if (mode & FALLOC_FL_ZERO_RANGE) {
                ret = btrfs_zero_range(inode, offset, len, mode);
                btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
                return ret;
        }

        locked_end = alloc_end - 1;
        btrfs_lock_extent(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                          &cached_state);

        btrfs_assert_inode_range_clean(BTRFS_I(inode), alloc_start, locked_end);

        /* First, check if we exceed the qgroup limit */
        while (cur_offset < alloc_end) {
                em = btrfs_get_extent(BTRFS_I(inode), NULL, cur_offset,
                                      alloc_end - cur_offset);
                if (IS_ERR(em)) {
                        ret = PTR_ERR(em);
                        break;
                }
                last_byte = min(btrfs_extent_map_end(em), alloc_end);
                actual_end = min_t(u64, btrfs_extent_map_end(em), offset + len);
                last_byte = ALIGN(last_byte, blocksize);
                if (em->disk_bytenr == EXTENT_MAP_HOLE ||
                    (cur_offset >= inode->i_size &&
                     !(em->flags & EXTENT_FLAG_PREALLOC))) {
                        const u64 range_len = last_byte - cur_offset;

                        ret = add_falloc_range(&reserve_list, cur_offset, range_len);
                        if (ret < 0) {
                                btrfs_free_extent_map(em);
                                break;
                        }
                        ret = btrfs_qgroup_reserve_data(BTRFS_I(inode),
                                        &data_reserved, cur_offset, range_len);
                        if (ret < 0) {
                                btrfs_free_extent_map(em);
                                break;
                        }
                        qgroup_reserved += range_len;
                        data_space_needed += range_len;
                }
                btrfs_free_extent_map(em);
                cur_offset = last_byte;
        }

        if (!ret && data_space_needed > 0) {
                /*
                 * We are safe to reserve space here as we can't have delalloc
                 * in the range, see above.
                 */
                ret = btrfs_alloc_data_chunk_ondemand(BTRFS_I(inode),
                                                      data_space_needed);
                if (!ret)
                        data_space_reserved = data_space_needed;
        }

        /*
         * If ret is still 0, means we're OK to fallocate.
         * Or just cleanup the list and exit.
         */
        list_for_each_entry_safe(range, tmp, &reserve_list, list) {
                if (!ret) {
                        ret = btrfs_prealloc_file_range(inode, mode,
                                        range->start,
                                        range->len, blocksize,
                                        offset + len, &alloc_hint);
                        /*
                         * btrfs_prealloc_file_range() releases space even
                         * if it returns an error.
                         */
                        data_space_reserved -= range->len;
                        qgroup_reserved -= range->len;
                } else if (data_space_reserved > 0) {
                        btrfs_free_reserved_data_space(BTRFS_I(inode),
                                               data_reserved, range->start,
                                               range->len);
                        data_space_reserved -= range->len;
                        qgroup_reserved -= range->len;
                } else if (qgroup_reserved > 0) {
                        btrfs_qgroup_free_data(BTRFS_I(inode), data_reserved,
                                               range->start, range->len, NULL);
                        qgroup_reserved -= range->len;
                }
                list_del(&range->list);
                kfree(range);
        }
        if (ret < 0)
                goto out_unlock;

        /*
         * We didn't need to allocate any more space, but we still extended the
         * size of the file so we need to update i_size and the inode item.
         */
        ret = btrfs_fallocate_update_isize(inode, actual_end, mode);
out_unlock:
        btrfs_unlock_extent(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                            &cached_state);
out:
        btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
        extent_changeset_free(data_reserved);
        return ret;
}

/*
 * Helper for btrfs_find_delalloc_in_range(). Find a subrange in a given range
 * that has unflushed and/or flushing delalloc. There might be other adjacent
 * subranges after the one it found, so btrfs_find_delalloc_in_range() keeps
 * looping while it gets adjacent subranges, and merging them together.
 */
static bool find_delalloc_subrange(struct btrfs_inode *inode, u64 start, u64 end,
                                   struct extent_state **cached_state,
                                   bool *search_io_tree,
                                   u64 *delalloc_start_ret, u64 *delalloc_end_ret)
{
        u64 len = end + 1 - start;
        u64 delalloc_len = 0;
        struct btrfs_ordered_extent *oe;
        u64 oe_start;
        u64 oe_end;

        /*
         * Search the io tree first for EXTENT_DELALLOC. If we find any, it
         * means we have delalloc (dirty pages) for which writeback has not
         * started yet.
         */
        if (*search_io_tree) {
                spin_lock(&inode->lock);
                if (inode->delalloc_bytes > 0) {
                        spin_unlock(&inode->lock);
                        *delalloc_start_ret = start;
                        delalloc_len = btrfs_count_range_bits(&inode->io_tree,
                                                              delalloc_start_ret, end,
                                                              len, EXTENT_DELALLOC, 1,
                                                              cached_state);
                } else {
                        spin_unlock(&inode->lock);
                }
        }

        if (delalloc_len > 0) {
                /*
                 * If delalloc was found then *delalloc_start_ret has a sector size
                 * aligned value (rounded down).
                 */
                *delalloc_end_ret = *delalloc_start_ret + delalloc_len - 1;

                if (*delalloc_start_ret == start) {
                        /* Delalloc for the whole range, nothing more to do. */
                        if (*delalloc_end_ret == end)
                                return true;
                        /* Else trim our search range for ordered extents. */
                        start = *delalloc_end_ret + 1;
                        len = end + 1 - start;
                }
        } else {
                /* No delalloc, future calls don't need to search again. */
                *search_io_tree = false;
        }

        /*
         * Now also check if there's any ordered extent in the range.
         * We do this because:
         *
         * 1) When delalloc is flushed, the file range is locked, we clear the
         *    EXTENT_DELALLOC bit from the io tree and create an extent map and
         *    an ordered extent for the write. So we might just have been called
         *    after delalloc is flushed and before the ordered extent completes
         *    and inserts the new file extent item in the subvolume's btree;
         *
         * 2) We may have an ordered extent created by flushing delalloc for a
         *    subrange that starts before the subrange we found marked with
         *    EXTENT_DELALLOC in the io tree.
         *
         * We could also use the extent map tree to find such delalloc that is
         * being flushed, but using the ordered extents tree is more efficient
         * because it's usually much smaller as ordered extents are removed from
         * the tree once they complete. With the extent maps, we may have them
         * in the extent map tree for a very long time, and they were either
         * created by previous writes or loaded by read operations.
         */
        oe = btrfs_lookup_first_ordered_range(inode, start, len);
        if (!oe)
                return (delalloc_len > 0);

        /* The ordered extent may span beyond our search range. */
        oe_start = max(oe->file_offset, start);
        oe_end = min(oe->file_offset + oe->num_bytes - 1, end);

        btrfs_put_ordered_extent(oe);

        /* Don't have unflushed delalloc, return the ordered extent range. */
        if (delalloc_len == 0) {
                *delalloc_start_ret = oe_start;
                *delalloc_end_ret = oe_end;
                return true;
        }

        /*
         * We have both unflushed delalloc (io_tree) and an ordered extent.
         * If the ranges are adjacent returned a combined range, otherwise
         * return the leftmost range.
         */
        if (oe_start < *delalloc_start_ret) {
                if (oe_end < *delalloc_start_ret)
                        *delalloc_end_ret = oe_end;
                *delalloc_start_ret = oe_start;
        } else if (*delalloc_end_ret + 1 == oe_start) {
                *delalloc_end_ret = oe_end;
        }

        return true;
}

/*
 * Check if there's delalloc in a given range.
 *
 * @inode:               The inode.
 * @start:               The start offset of the range. It does not need to be
 *                       sector size aligned.
 * @end:                 The end offset (inclusive value) of the search range.
 *                       It does not need to be sector size aligned.
 * @cached_state:        Extent state record used for speeding up delalloc
 *                       searches in the inode's io_tree. Can be NULL.
 * @delalloc_start_ret:  Output argument, set to the start offset of the
 *                       subrange found with delalloc (may not be sector size
 *                       aligned).
 * @delalloc_end_ret:    Output argument, set to he end offset (inclusive value)
 *                       of the subrange found with delalloc.
 *
 * Returns true if a subrange with delalloc is found within the given range, and
 * if so it sets @delalloc_start_ret and @delalloc_end_ret with the start and
 * end offsets of the subrange.
 */
bool btrfs_find_delalloc_in_range(struct btrfs_inode *inode, u64 start, u64 end,
                                  struct extent_state **cached_state,
                                  u64 *delalloc_start_ret, u64 *delalloc_end_ret)
{
        u64 cur_offset = round_down(start, inode->root->fs_info->sectorsize);
        u64 prev_delalloc_end = 0;
        bool search_io_tree = true;
        bool ret = false;

        while (cur_offset <= end) {
                u64 delalloc_start;
                u64 delalloc_end;
                bool delalloc;

                delalloc = find_delalloc_subrange(inode, cur_offset, end,
                                                  cached_state, &search_io_tree,
                                                  &delalloc_start,
                                                  &delalloc_end);
                if (!delalloc)
                        break;

                if (prev_delalloc_end == 0) {
                        /* First subrange found. */
                        *delalloc_start_ret = max(delalloc_start, start);
                        *delalloc_end_ret = delalloc_end;
                        ret = true;
                } else if (delalloc_start == prev_delalloc_end + 1) {
                        /* Subrange adjacent to the previous one, merge them. */
                        *delalloc_end_ret = delalloc_end;
                } else {
                        /* Subrange not adjacent to the previous one, exit. */
                        break;
                }

                prev_delalloc_end = delalloc_end;
                cur_offset = delalloc_end + 1;
                cond_resched();
        }

        return ret;
}

/*
 * Check if there's a hole or delalloc range in a range representing a hole (or
 * prealloc extent) found in the inode's subvolume btree.
 *
 * @inode:      The inode.
 * @whence:     Seek mode (SEEK_DATA or SEEK_HOLE).
 * @start:      Start offset of the hole region. It does not need to be sector
 *              size aligned.
 * @end:        End offset (inclusive value) of the hole region. It does not
 *              need to be sector size aligned.
 * @start_ret:  Return parameter, used to set the start of the subrange in the
 *              hole that matches the search criteria (seek mode), if such
 *              subrange is found (return value of the function is true).
 *              The value returned here may not be sector size aligned.
 *
 * Returns true if a subrange matching the given seek mode is found, and if one
 * is found, it updates @start_ret with the start of the subrange.
 */
static bool find_desired_extent_in_hole(struct btrfs_inode *inode, int whence,
                                        struct extent_state **cached_state,
                                        u64 start, u64 end, u64 *start_ret)
{
        u64 delalloc_start;
        u64 delalloc_end;
        bool delalloc;

        delalloc = btrfs_find_delalloc_in_range(inode, start, end, cached_state,
                                                &delalloc_start, &delalloc_end);
        if (delalloc && whence == SEEK_DATA) {
                *start_ret = delalloc_start;
                return true;
        }

        if (delalloc && whence == SEEK_HOLE) {
                /*
                 * We found delalloc but it starts after out start offset. So we
                 * have a hole between our start offset and the delalloc start.
                 */
                if (start < delalloc_start) {
                        *start_ret = start;
                        return true;
                }
                /*
                 * Delalloc range starts at our start offset.
                 * If the delalloc range's length is smaller than our range,
                 * then it means we have a hole that starts where the delalloc
                 * subrange ends.
                 */
                if (delalloc_end < end) {
                        *start_ret = delalloc_end + 1;
                        return true;
                }

                /* There's delalloc for the whole range. */
                return false;
        }

        if (!delalloc && whence == SEEK_HOLE) {
                *start_ret = start;
                return true;
        }

        /*
         * No delalloc in the range and we are seeking for data. The caller has
         * to iterate to the next extent item in the subvolume btree.
         */
        return false;
}

static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
{
        struct btrfs_inode *inode = BTRFS_I(file->f_mapping->host);
        struct btrfs_file_private *private;
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_state *cached_state = NULL;
        struct extent_state **delalloc_cached_state;
        const loff_t i_size = i_size_read(&inode->vfs_inode);
        const u64 ino = btrfs_ino(inode);
        struct btrfs_root *root = inode->root;
        struct btrfs_path *path;
        struct btrfs_key key;
        u64 last_extent_end;
        u64 lockstart;
        u64 lockend;
        u64 start;
        int ret;
        bool found = false;

        if (i_size == 0 || offset >= i_size)
                return -ENXIO;

        /*
         * Quick path. If the inode has no prealloc extents and its number of
         * bytes used matches its i_size, then it can not have holes.
         */
        if (whence == SEEK_HOLE &&
            !(inode->flags & BTRFS_INODE_PREALLOC) &&
            inode_get_bytes(&inode->vfs_inode) == i_size)
                return i_size;

        spin_lock(&inode->lock);
        private = file->private_data;
        spin_unlock(&inode->lock);

        if (private && private->owner_task != current) {
                /*
                 * Not allocated by us, don't use it as its cached state is used
                 * by the task that allocated it and we don't want neither to
                 * mess with it nor get incorrect results because it reflects an
                 * invalid state for the current task.
                 */
                private = NULL;
        } else if (!private) {
                private = kzalloc_obj(*private);
                /*
                 * No worries if memory allocation failed.
                 * The private structure is used only for speeding up multiple
                 * lseek SEEK_HOLE/DATA calls to a file when there's delalloc,
                 * so everything will still be correct.
                 */
                if (private) {
                        bool free = false;

                        private->owner_task = current;

                        spin_lock(&inode->lock);
                        if (file->private_data)
                                free = true;
                        else
                                file->private_data = private;
                        spin_unlock(&inode->lock);

                        if (free) {
                                kfree(private);
                                private = NULL;
                        }
                }
        }

        if (private)
                delalloc_cached_state = &private->llseek_cached_state;
        else
                delalloc_cached_state = NULL;

        /*
         * offset can be negative, in this case we start finding DATA/HOLE from
         * the very start of the file.
         */
        start = max_t(loff_t, 0, offset);

        lockstart = round_down(start, fs_info->sectorsize);
        lockend = round_up(i_size, fs_info->sectorsize);
        if (lockend <= lockstart)
                lockend = lockstart + fs_info->sectorsize;
        lockend--;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->reada = READA_FORWARD;

        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = start;

        last_extent_end = lockstart;

        btrfs_lock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0) {
                goto out;
        } else if (ret > 0 && path->slots[0] > 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
                if (key.objectid == ino && key.type == BTRFS_EXTENT_DATA_KEY)
                        path->slots[0]--;
        }

        while (start < i_size) {
                struct extent_buffer *leaf = path->nodes[0];
                struct btrfs_file_extent_item *extent;
                u64 extent_end;
                u8 type;

                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;

                        leaf = path->nodes[0];
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
                        break;

                extent_end = btrfs_file_extent_end(path);

                /*
                 * In the first iteration we may have a slot that points to an
                 * extent that ends before our start offset, so skip it.
                 */
                if (extent_end <= start) {
                        path->slots[0]++;
                        continue;
                }

                /* We have an implicit hole, NO_HOLES feature is likely set. */
                if (last_extent_end < key.offset) {
                        u64 search_start = last_extent_end;
                        u64 found_start;

                        /*
                         * First iteration, @start matches @offset and it's
                         * within the hole.
                         */
                        if (start == offset)
                                search_start = offset;

                        found = find_desired_extent_in_hole(inode, whence,
                                                            delalloc_cached_state,
                                                            search_start,
                                                            key.offset - 1,
                                                            &found_start);
                        if (found) {
                                start = found_start;
                                break;
                        }
                        /*
                         * Didn't find data or a hole (due to delalloc) in the
                         * implicit hole range, so need to analyze the extent.
                         */
                }

                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(leaf, extent);

                /*
                 * Can't access the extent's disk_bytenr field if this is an
                 * inline extent, since at that offset, it's where the extent
                 * data starts.
                 */
                if (type == BTRFS_FILE_EXTENT_PREALLOC ||
                    (type == BTRFS_FILE_EXTENT_REG &&
                     btrfs_file_extent_disk_bytenr(leaf, extent) == 0)) {
                        /*
                         * Explicit hole or prealloc extent, search for delalloc.
                         * A prealloc extent is treated like a hole.
                         */
                        u64 search_start = key.offset;
                        u64 found_start;

                        /*
                         * First iteration, @start matches @offset and it's
                         * within the hole.
                         */
                        if (start == offset)
                                search_start = offset;

                        found = find_desired_extent_in_hole(inode, whence,
                                                            delalloc_cached_state,
                                                            search_start,
                                                            extent_end - 1,
                                                            &found_start);
                        if (found) {
                                start = found_start;
                                break;
                        }
                        /*
                         * Didn't find data or a hole (due to delalloc) in the
                         * implicit hole range, so need to analyze the next
                         * extent item.
                         */
                } else {
                        /*
                         * Found a regular or inline extent.
                         * If we are seeking for data, adjust the start offset
                         * and stop, we're done.
                         */
                        if (whence == SEEK_DATA) {
                                start = max_t(u64, key.offset, offset);
                                found = true;
                                break;
                        }
                        /*
                         * Else, we are seeking for a hole, check the next file
                         * extent item.
                         */
                }

                start = extent_end;
                last_extent_end = extent_end;
                path->slots[0]++;
                if (fatal_signal_pending(current)) {
                        ret = -EINTR;
                        goto out;
                }
                cond_resched();
        }

        /* We have an implicit hole from the last extent found up to i_size. */
        if (!found && start < i_size) {
                found = find_desired_extent_in_hole(inode, whence,
                                                    delalloc_cached_state, start,
                                                    i_size - 1, &start);
                if (!found)
                        start = i_size;
        }

out:
        btrfs_unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
        btrfs_free_path(path);

        if (ret < 0)
                return ret;

        if (whence == SEEK_DATA && start >= i_size)
                return -ENXIO;

        return min_t(loff_t, start, i_size);
}

static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;

        switch (whence) {
        default:
                return generic_file_llseek(file, offset, whence);
        case SEEK_DATA:
        case SEEK_HOLE:
                btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
                offset = find_desired_extent(file, offset, whence);
                btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
                break;
        }

        if (offset < 0)
                return offset;

        return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
}

static int btrfs_file_open(struct inode *inode, struct file *filp)
{
        int ret;

        if (btrfs_is_shutdown(inode_to_fs_info(inode)))
                return -EIO;

        filp->f_mode |= FMODE_NOWAIT | FMODE_CAN_ODIRECT;

        ret = fsverity_file_open(inode, filp);
        if (ret)
                return ret;
        return generic_file_open(inode, filp);
}

static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        ssize_t ret = 0;

        if (btrfs_is_shutdown(inode_to_fs_info(file_inode(iocb->ki_filp))))
                return -EIO;

        if (iocb->ki_flags & IOCB_DIRECT) {
                ret = btrfs_direct_read(iocb, to);
                if (ret < 0 || !iov_iter_count(to) ||
                    iocb->ki_pos >= i_size_read(file_inode(iocb->ki_filp)))
                        return ret;
        }

        return filemap_read(iocb, to, ret);
}

static ssize_t btrfs_file_splice_read(struct file *in, loff_t *ppos,
                                      struct pipe_inode_info *pipe,
                                      size_t len, unsigned int flags)
{
        if (btrfs_is_shutdown(inode_to_fs_info(file_inode(in))))
                return -EIO;

        return filemap_splice_read(in, ppos, pipe, len, flags);
}

const struct file_operations btrfs_file_operations = {
        .llseek         = btrfs_file_llseek,
        .read_iter      = btrfs_file_read_iter,
        .splice_read    = btrfs_file_splice_read,
        .write_iter     = btrfs_file_write_iter,
        .splice_write   = iter_file_splice_write,
        .mmap_prepare   = btrfs_file_mmap_prepare,
        .open           = btrfs_file_open,
        .release        = btrfs_release_file,
        .get_unmapped_area = thp_get_unmapped_area,
        .fsync          = btrfs_sync_file,
        .fallocate      = btrfs_fallocate,
        .unlocked_ioctl = btrfs_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = btrfs_compat_ioctl,
#endif
        .remap_file_range = btrfs_remap_file_range,
        .uring_cmd      = btrfs_uring_cmd,
        .fop_flags      = FOP_BUFFER_RASYNC | FOP_BUFFER_WASYNC,
        .setlease       = generic_setlease,
};

int btrfs_fdatawrite_range(struct btrfs_inode *inode, loff_t start, loff_t end)
{
        struct address_space *mapping = inode->vfs_inode.i_mapping;
        int ret;

        /*
         * So with compression we will find and lock a dirty page and clear the
         * first one as dirty, setup an async extent, and immediately return
         * with the entire range locked but with nobody actually marked with
         * writeback.  So we can't just filemap_write_and_wait_range() and
         * expect it to work since it will just kick off a thread to do the
         * actual work.  So we need to call filemap_fdatawrite_range _again_
         * since it will wait on the page lock, which won't be unlocked until
         * after the pages have been marked as writeback and so we're good to go
         * from there.  We have to do this otherwise we'll miss the ordered
         * extents and that results in badness.  Please Josef, do not think you
         * know better and pull this out at some point in the future, it is
         * right and you are wrong.
         */
        ret = filemap_fdatawrite_range(mapping, start, end);
        if (!ret && test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT, &inode->runtime_flags))
                ret = filemap_fdatawrite_range(mapping, start, end);

        return ret;
}