linux/fs/btrfs/fiemap.c

// SPDX-License-Identifier: GPL-2.0

#include "backref.h"
#include "btrfs_inode.h"
#include "fiemap.h"
#include "file.h"
#include "file-item.h"

struct btrfs_fiemap_entry {
	u64 offset;
	u64 phys;
	u64 len;
	u32 flags;
};

/*
 * Indicate the caller of emit_fiemap_extent() that it needs to unlock the file
 * range from the inode's io tree, unlock the subvolume tree search path, flush
 * the fiemap cache and relock the file range and research the subvolume tree.
 * The value here is something negative that can't be confused with a valid
 * errno value and different from 1 because that's also a return value from
 * fiemap_fill_next_extent() and also it's often used to mean some btree search
 * did not find a key, so make it some distinct negative value.
 */
#define BTRFS_FIEMAP_FLUSH_CACHE (-(MAX_ERRNO + 1))

/*
 * Used to:
 *
 * - Cache the next entry to be emitted to the fiemap buffer, so that we can
 *   merge extents that are contiguous and can be grouped as a single one;
 *
 * - Store extents ready to be written to the fiemap buffer in an intermediary
 *   buffer. This intermediary buffer is to ensure that in case the fiemap
 *   buffer is memory mapped to the fiemap target file, we don't deadlock
 *   during btrfs_page_mkwrite(). This is because during fiemap we are locking
 *   an extent range in order to prevent races with delalloc flushing and
 *   ordered extent completion, which is needed in order to reliably detect
 *   delalloc in holes and prealloc extents. And this can lead to a deadlock
 *   if the fiemap buffer is memory mapped to the file we are running fiemap
 *   against (a silly, useless in practice scenario, but possible) because
 *   btrfs_page_mkwrite() will try to lock the same extent range.
 */
struct fiemap_cache {
	/* An array of ready fiemap entries. */
	struct btrfs_fiemap_entry *entries;
	/* Number of entries in the entries array. */
	int entries_size;
	/* Index of the next entry in the entries array to write to. */
	int entries_pos;
	/*
	 * Once the entries array is full, this indicates what's the offset for
	 * the next file extent item we must search for in the inode's subvolume
	 * tree after unlocking the extent range in the inode's io tree and
	 * releasing the search path.
	 */
	u64 next_search_offset;
	/*
	 * This matches struct fiemap_extent_info::fi_mapped_extents, we use it
	 * to count ourselves emitted extents and stop instead of relying on
	 * fiemap_fill_next_extent() because we buffer ready fiemap entries at
	 * the @entries array, and we want to stop as soon as we hit the max
	 * amount of extents to map, not just to save time but also to make the
	 * logic at extent_fiemap() simpler.
	 */
	unsigned int extents_mapped;
	/* Fields for the cached extent (unsubmitted, not ready, extent). */
	u64 offset;
	u64 phys;
	u64 len;
	u32 flags;
	bool cached;
};

static int flush_fiemap_cache(struct fiemap_extent_info *fieinfo,
			      struct fiemap_cache *cache)
{
	for (int i = 0; i < cache->entries_pos; i++) {
		struct btrfs_fiemap_entry *entry = &cache->entries[i];
		int ret;

		ret = fiemap_fill_next_extent(fieinfo, entry->offset,
					      entry->phys, entry->len,
					      entry->flags);
		/*
		 * Ignore 1 (reached max entries) because we keep track of that
		 * ourselves in emit_fiemap_extent().
		 */
		if (ret < 0)
			return ret;
	}
	cache->entries_pos = 0;

	return 0;
}

/*
 * Helper to submit fiemap extent.
 *
 * Will try to merge current fiemap extent specified by @offset, @phys,
 * @len and @flags with cached one.
 * And only when we fails to merge, cached one will be submitted as
 * fiemap extent.
 *
 * Return value is the same as fiemap_fill_next_extent().
 */
static int emit_fiemap_extent(struct fiemap_extent_info *fieinfo,
				struct fiemap_cache *cache,
				u64 offset, u64 phys, u64 len, u32 flags)
{
	struct btrfs_fiemap_entry *entry;
	u64 cache_end;

	/* Set at the end of extent_fiemap(). */
	ASSERT((flags & FIEMAP_EXTENT_LAST) == 0);

	if (!cache->cached)
		goto assign;

	/*
	 * When iterating the extents of the inode, at extent_fiemap(), we may
	 * find an extent that starts at an offset behind the end offset of the
	 * previous extent we processed. This happens if fiemap is called
	 * without FIEMAP_FLAG_SYNC and there are ordered extents completing
	 * after we had to unlock the file range, release the search path, emit
	 * the fiemap extents stored in the buffer (cache->entries array) and
	 * the lock the remainder of the range and re-search the btree.
	 *
	 * For example we are in leaf X processing its last item, which is the
	 * file extent item for file range [512K, 1M[, and after
	 * btrfs_next_leaf() releases the path, there's an ordered extent that
	 * completes for the file range [768K, 2M[, and that results in trimming
	 * the file extent item so that it now corresponds to the file range
	 * [512K, 768K[ and a new file extent item is inserted for the file
	 * range [768K, 2M[, which may end up as the last item of leaf X or as
	 * the first item of the next leaf - in either case btrfs_next_leaf()
	 * will leave us with a path pointing to the new extent item, for the
	 * file range [768K, 2M[, since that's the first key that follows the
	 * last one we processed. So in order not to report overlapping extents
	 * to user space, we trim the length of the previously cached extent and
	 * emit it.
	 *
	 * Upon calling btrfs_next_leaf() we may also find an extent with an
	 * offset smaller than or equals to cache->offset, and this happens
	 * when we had a hole or prealloc extent with several delalloc ranges in
	 * it, but after btrfs_next_leaf() released the path, delalloc was
	 * flushed and the resulting ordered extents were completed, so we can
	 * now have found a file extent item for an offset that is smaller than
	 * or equals to what we have in cache->offset. We deal with this as
	 * described below.
	 */
	cache_end = cache->offset + cache->len;
	if (cache_end > offset) {
		if (offset == cache->offset) {
			/*
			 * We cached a dealloc range (found in the io tree) for
			 * a hole or prealloc extent and we have now found a
			 * file extent item for the same offset. What we have
			 * now is more recent and up to date, so discard what
			 * we had in the cache and use what we have just found.
			 */
			goto assign;
		} else if (offset > cache->offset) {
			/*
			 * The extent range we previously found ends after the
			 * offset of the file extent item we found and that
			 * offset falls somewhere in the middle of that previous
			 * extent range. So adjust the range we previously found
			 * to end at the offset of the file extent item we have
			 * just found, since this extent is more up to date.
			 * Emit that adjusted range and cache the file extent
			 * item we have just found. This corresponds to the case
			 * where a previously found file extent item was split
			 * due to an ordered extent completing.
			 */
			cache->len = offset - cache->offset;
			goto emit;
		} else {
			const u64 range_end = offset + len;

			/*
			 * The offset of the file extent item we have just found
			 * is behind the cached offset. This means we were
			 * processing a hole or prealloc extent for which we
			 * have found delalloc ranges (in the io tree), so what
			 * we have in the cache is the last delalloc range we
			 * found while the file extent item we found can be
			 * either for a whole delalloc range we previously
			 * emmitted or only a part of that range.
			 *
			 * We have two cases here:
			 *
			 * 1) The file extent item's range ends at or behind the
			 *    cached extent's end. In this case just ignore the
			 *    current file extent item because we don't want to
			 *    overlap with previous ranges that may have been
			 *    emmitted already;
			 *
			 * 2) The file extent item starts behind the currently
			 *    cached extent but its end offset goes beyond the
			 *    end offset of the cached extent. We don't want to
			 *    overlap with a previous range that may have been
			 *    emmitted already, so we emit the currently cached
			 *    extent and then partially store the current file
			 *    extent item's range in the cache, for the subrange
			 *    going the cached extent's end to the end of the
			 *    file extent item.
			 */
			if (range_end <= cache_end)
				return 0;

			if (!(flags & (FIEMAP_EXTENT_ENCODED | FIEMAP_EXTENT_DELALLOC)))
				phys += cache_end - offset;

			offset = cache_end;
			len = range_end - cache_end;
			goto emit;
		}
	}

	/*
	 * Only merges fiemap extents if
	 * 1) Their logical addresses are continuous
	 *
	 * 2) Their physical addresses are continuous
	 *    So truly compressed (physical size smaller than logical size)
	 *    extents won't get merged with each other
	 *
	 * 3) Share same flags
	 */
	if (cache->offset + cache->len  == offset &&
	    cache->phys + cache->len == phys  &&
	    cache->flags == flags) {
		cache->len += len;
		return 0;
	}

emit:
	/* Not mergeable, need to submit cached one */

	if (cache->entries_pos == cache->entries_size) {
		/*
		 * We will need to research for the end offset of the last
		 * stored extent and not from the current offset, because after
		 * unlocking the range and releasing the path, if there's a hole
		 * between that end offset and this current offset, a new extent
		 * may have been inserted due to a new write, so we don't want
		 * to miss it.
		 */
		entry = &cache->entries[cache->entries_size - 1];
		cache->next_search_offset = entry->offset + entry->len;
		cache->cached = false;

		return BTRFS_FIEMAP_FLUSH_CACHE;
	}

	entry = &cache->entries[cache->entries_pos];
	entry->offset = cache->offset;
	entry->phys = cache->phys;
	entry->len = cache->len;
	entry->flags = cache->flags;
	cache->entries_pos++;
	cache->extents_mapped++;

	if (cache->extents_mapped == fieinfo->fi_extents_max) {
		cache->cached = false;
		return 1;
	}
assign:
	cache->cached = true;
	cache->offset = offset;
	cache->phys = phys;
	cache->len = len;
	cache->flags = flags;

	return 0;
}

/*
 * Emit last fiemap cache
 *
 * The last fiemap cache may still be cached in the following case:
 * 0		      4k		    8k
 * |<- Fiemap range ->|
 * |<------------  First extent ----------->|
 *
 * In this case, the first extent range will be cached but not emitted.
 * So we must emit it before ending extent_fiemap().
 */
static int emit_last_fiemap_cache(struct fiemap_extent_info *fieinfo,
				  struct fiemap_cache *cache)
{
	int ret;

	if (!cache->cached)
		return 0;

	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
				      cache->len, cache->flags);
	cache->cached = false;
	if (ret > 0)
		ret = 0;
	return ret;
}

static int fiemap_next_leaf_item(struct btrfs_inode *inode, struct btrfs_path *path)
{
	struct extent_buffer *clone = path->nodes[0];
	struct btrfs_key key;
	int slot;
	int ret;

	path->slots[0]++;
	if (path->slots[0] < btrfs_header_nritems(path->nodes[0]))
		return 0;

	/*
	 * Add a temporary extra ref to an already cloned extent buffer to
	 * prevent btrfs_next_leaf() freeing it, we want to reuse it to avoid
	 * the cost of allocating a new one.
	 */
	ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED, &clone->bflags));
	atomic_inc(&clone->refs);

	ret = btrfs_next_leaf(inode->root, path);
	if (ret != 0)
		goto out;

	/*
	 * Don't bother with cloning if there are no more file extent items for
	 * our inode.
	 */
	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
	if (key.objectid != btrfs_ino(inode) || key.type != BTRFS_EXTENT_DATA_KEY) {
		ret = 1;
		goto out;
	}

	/*
	 * Important to preserve the start field, for the optimizations when
	 * checking if extents are shared (see extent_fiemap()).
	 *
	 * We must set ->start before calling copy_extent_buffer_full().  If we
	 * are on sub-pagesize blocksize, we use ->start to determine the offset
	 * into the folio where our eb exists, and if we update ->start after
	 * the fact then any subsequent reads of the eb may read from a
	 * different offset in the folio than where we originally copied into.
	 */
	clone->start = path->nodes[0]->start;
	/* See the comment at fiemap_search_slot() about why we clone. */
	copy_extent_buffer_full(clone, path->nodes[0]);

	slot = path->slots[0];
	btrfs_release_path(path);
	path->nodes[0] = clone;
	path->slots[0] = slot;
out:
	if (ret)
		free_extent_buffer(clone);

	return ret;
}

/*
 * Search for the first file extent item that starts at a given file offset or
 * the one that starts immediately before that offset.
 * Returns: 0 on success, < 0 on error, 1 if not found.
 */
static int fiemap_search_slot(struct btrfs_inode *inode, struct btrfs_path *path,
			      u64 file_offset)
{
	const u64 ino = btrfs_ino(inode);
	struct btrfs_root *root = inode->root;
	struct extent_buffer *clone;
	struct btrfs_key key;
	int slot;
	int ret;

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

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		return ret;

	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]--;
	}

	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
		ret = btrfs_next_leaf(root, path);
		if (ret != 0)
			return ret;

		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
		if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
			return 1;
	}

	/*
	 * We clone the leaf and use it during fiemap. This is because while
	 * using the leaf we do expensive things like checking if an extent is
	 * shared, which can take a long time. In order to prevent blocking
	 * other tasks for too long, we use a clone of the leaf. We have locked
	 * the file range in the inode's io tree, so we know none of our file
	 * extent items can change. This way we avoid blocking other tasks that
	 * want to insert items for other inodes in the same leaf or b+tree
	 * rebalance operations (triggered for example when someone is trying
	 * to push items into this leaf when trying to insert an item in a
	 * neighbour leaf).
	 * We also need the private clone because holding a read lock on an
	 * extent buffer of the subvolume's b+tree will make lockdep unhappy
	 * when we check if extents are shared, as backref walking may need to
	 * lock the same leaf we are processing.
	 */
	clone = btrfs_clone_extent_buffer(path->nodes[0]);
	if (!clone)
		return -ENOMEM;

	slot = path->slots[0];
	btrfs_release_path(path);
	path->nodes[0] = clone;
	path->slots[0] = slot;

	return 0;
}

/*
 * Process a range which is a hole or a prealloc extent in the inode's subvolume
 * btree. If @disk_bytenr is 0, we are dealing with a hole, otherwise a prealloc
 * extent. The end offset (@end) is inclusive.
 */
static int fiemap_process_hole(struct btrfs_inode *inode,
			       struct fiemap_extent_info *fieinfo,
			       struct fiemap_cache *cache,
			       struct extent_state **delalloc_cached_state,
			       struct btrfs_backref_share_check_ctx *backref_ctx,
			       u64 disk_bytenr, u64 extent_offset,
			       u64 extent_gen,
			       u64 start, u64 end)
{
	const u64 i_size = i_size_read(&inode->vfs_inode);
	u64 cur_offset = start;
	u64 last_delalloc_end = 0;
	u32 prealloc_flags = FIEMAP_EXTENT_UNWRITTEN;
	bool checked_extent_shared = false;
	int ret;

	/*
	 * There can be no delalloc past i_size, so don't waste time looking for
	 * it beyond i_size.
	 */
	while (cur_offset < end && cur_offset < i_size) {
		u64 delalloc_start;
		u64 delalloc_end;
		u64 prealloc_start;
		u64 prealloc_len = 0;
		bool delalloc;

		delalloc = btrfs_find_delalloc_in_range(inode, cur_offset, end,
							delalloc_cached_state,
							&delalloc_start,
							&delalloc_end);
		if (!delalloc)
			break;

		/*
		 * If this is a prealloc extent we have to report every section
		 * of it that has no delalloc.
		 */
		if (disk_bytenr != 0) {
			if (last_delalloc_end == 0) {
				prealloc_start = start;
				prealloc_len = delalloc_start - start;
			} else {
				prealloc_start = last_delalloc_end + 1;
				prealloc_len = delalloc_start - prealloc_start;
			}
		}

		if (prealloc_len > 0) {
			if (!checked_extent_shared && fieinfo->fi_extents_max) {
				ret = btrfs_is_data_extent_shared(inode,
								  disk_bytenr,
								  extent_gen,
								  backref_ctx);
				if (ret < 0)
					return ret;
				else if (ret > 0)
					prealloc_flags |= FIEMAP_EXTENT_SHARED;

				checked_extent_shared = true;
			}
			ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
						 disk_bytenr + extent_offset,
						 prealloc_len, prealloc_flags);
			if (ret)
				return ret;
			extent_offset += prealloc_len;
		}

		ret = emit_fiemap_extent(fieinfo, cache, delalloc_start, 0,
					 delalloc_end + 1 - delalloc_start,
					 FIEMAP_EXTENT_DELALLOC |
					 FIEMAP_EXTENT_UNKNOWN);
		if (ret)
			return ret;

		last_delalloc_end = delalloc_end;
		cur_offset = delalloc_end + 1;
		extent_offset += cur_offset - delalloc_start;
		cond_resched();
	}

	/*
	 * Either we found no delalloc for the whole prealloc extent or we have
	 * a prealloc extent that spans i_size or starts at or after i_size.
	 */
	if (disk_bytenr != 0 && last_delalloc_end < end) {
		u64 prealloc_start;
		u64 prealloc_len;

		if (last_delalloc_end == 0) {
			prealloc_start = start;
			prealloc_len = end + 1 - start;
		} else {
			prealloc_start = last_delalloc_end + 1;
			prealloc_len = end + 1 - prealloc_start;
		}

		if (!checked_extent_shared && fieinfo->fi_extents_max) {
			ret = btrfs_is_data_extent_shared(inode,
							  disk_bytenr,
							  extent_gen,
							  backref_ctx);
			if (ret < 0)
				return ret;
			else if (ret > 0)
				prealloc_flags |= FIEMAP_EXTENT_SHARED;
		}
		ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
					 disk_bytenr + extent_offset,
					 prealloc_len, prealloc_flags);
		if (ret)
			return ret;
	}

	return 0;
}

static int fiemap_find_last_extent_offset(struct btrfs_inode *inode,
					  struct btrfs_path *path,
					  u64 *last_extent_end_ret)
{
	const u64 ino = btrfs_ino(inode);
	struct btrfs_root *root = inode->root;
	struct extent_buffer *leaf;
	struct btrfs_file_extent_item *ei;
	struct btrfs_key key;
	u64 disk_bytenr;
	int ret;

	/*
	 * Lookup the last file extent. We're not using i_size here because
	 * there might be preallocation past i_size.
	 */
	ret = btrfs_lookup_file_extent(NULL, root, path, ino, (u64)-1, 0);
	/* There can't be a file extent item at offset (u64)-1 */
	ASSERT(ret != 0);
	if (ret < 0)
		return ret;

	/*
	 * For a non-existing key, btrfs_search_slot() always leaves us at a
	 * slot > 0, except if the btree is empty, which is impossible because
	 * at least it has the inode item for this inode and all the items for
	 * the root inode 256.
	 */
	ASSERT(path->slots[0] > 0);
	path->slots[0]--;
	leaf = path->nodes[0];
	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
	if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
		/* No file extent items in the subvolume tree. */
		*last_extent_end_ret = 0;
		return 0;
	}

	/*
	 * For an inline extent, the disk_bytenr is where inline data starts at,
	 * so first check if we have an inline extent item before checking if we
	 * have an implicit hole (disk_bytenr == 0).
	 */
	ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
	if (btrfs_file_extent_type(leaf, ei) == BTRFS_FILE_EXTENT_INLINE) {
		*last_extent_end_ret = btrfs_file_extent_end(path);
		return 0;
	}

	/*
	 * Find the last file extent item that is not a hole (when NO_HOLES is
	 * not enabled). This should take at most 2 iterations in the worst
	 * case: we have one hole file extent item at slot 0 of a leaf and
	 * another hole file extent item as the last item in the previous leaf.
	 * This is because we merge file extent items that represent holes.
	 */
	disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
	while (disk_bytenr == 0) {
		ret = btrfs_previous_item(root, path, ino, BTRFS_EXTENT_DATA_KEY);
		if (ret < 0) {
			return ret;
		} else if (ret > 0) {
			/* No file extent items that are not holes. */
			*last_extent_end_ret = 0;
			return 0;
		}
		leaf = path->nodes[0];
		ei = btrfs_item_ptr(leaf, path->slots[0],
				    struct btrfs_file_extent_item);
		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
	}

	*last_extent_end_ret = btrfs_file_extent_end(path);
	return 0;
}

static int extent_fiemap(struct btrfs_inode *inode,
			 struct fiemap_extent_info *fieinfo,
			 u64 start, u64 len)
{
	const u64 ino = btrfs_ino(inode);
	struct extent_state *cached_state = NULL;
	struct extent_state *delalloc_cached_state = NULL;
	struct btrfs_path *path;
	struct fiemap_cache cache = { 0 };
	struct btrfs_backref_share_check_ctx *backref_ctx;
	u64 last_extent_end = 0;
	u64 prev_extent_end;
	u64 range_start;
	u64 range_end;
	const u64 sectorsize = inode->root->fs_info->sectorsize;
	bool stopped = false;
	int ret;

	cache.entries_size = PAGE_SIZE / sizeof(struct btrfs_fiemap_entry);
	cache.entries = kmalloc_array(cache.entries_size,
				      sizeof(struct btrfs_fiemap_entry),
				      GFP_KERNEL);
	backref_ctx = btrfs_alloc_backref_share_check_ctx();
	path = btrfs_alloc_path();
	if (!cache.entries || !backref_ctx || !path) {
		ret = -ENOMEM;
		goto out;
	}

restart:
	range_start = round_down(start, sectorsize);
	range_end = round_up(start + len, sectorsize);
	prev_extent_end = range_start;

	lock_extent(&inode->io_tree, range_start, range_end, &cached_state);

	ret = fiemap_find_last_extent_offset(inode, path, &last_extent_end);
	if (ret < 0)
		goto out_unlock;
	btrfs_release_path(path);

	path->reada = READA_FORWARD;
	ret = fiemap_search_slot(inode, path, range_start);
	if (ret < 0) {
		goto out_unlock;
	} else if (ret > 0) {
		/*
		 * No file extent item found, but we may have delalloc between
		 * the current offset and i_size. So check for that.
		 */
		ret = 0;
		goto check_eof_delalloc;
	}

	while (prev_extent_end < range_end) {
		struct extent_buffer *leaf = path->nodes[0];
		struct btrfs_file_extent_item *ei;
		struct btrfs_key key;
		u64 extent_end;
		u64 extent_len;
		u64 extent_offset = 0;
		u64 extent_gen;
		u64 disk_bytenr = 0;
		u64 flags = 0;
		int extent_type;
		u8 compression;

		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);

		/*
		 * The first iteration can leave us at an extent item that ends
		 * before our range's start. Move to the next item.
		 */
		if (extent_end <= range_start)
			goto next_item;

		backref_ctx->curr_leaf_bytenr = leaf->start;

		/* We have in implicit hole (NO_HOLES feature enabled). */
		if (prev_extent_end < key.offset) {
			const u64 hole_end = min(key.offset, range_end) - 1;

			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx, 0, 0, 0,
						  prev_extent_end, hole_end);
			if (ret < 0) {
				goto out_unlock;
			} else if (ret > 0) {
				/* fiemap_fill_next_extent() told us to stop. */
				stopped = true;
				break;
			}

			/* We've reached the end of the fiemap range, stop. */
			if (key.offset >= range_end) {
				stopped = true;
				break;
			}
		}

		extent_len = extent_end - key.offset;
		ei = btrfs_item_ptr(leaf, path->slots[0],
				    struct btrfs_file_extent_item);
		compression = btrfs_file_extent_compression(leaf, ei);
		extent_type = btrfs_file_extent_type(leaf, ei);
		extent_gen = btrfs_file_extent_generation(leaf, ei);

		if (extent_type != BTRFS_FILE_EXTENT_INLINE) {
			disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
			if (compression == BTRFS_COMPRESS_NONE)
				extent_offset = btrfs_file_extent_offset(leaf, ei);
		}

		if (compression != BTRFS_COMPRESS_NONE)
			flags |= FIEMAP_EXTENT_ENCODED;

		if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
			flags |= FIEMAP_EXTENT_DATA_INLINE;
			flags |= FIEMAP_EXTENT_NOT_ALIGNED;
			ret = emit_fiemap_extent(fieinfo, &cache, key.offset, 0,
						 extent_len, flags);
		} else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx,
						  disk_bytenr, extent_offset,
						  extent_gen, key.offset,
						  extent_end - 1);
		} else if (disk_bytenr == 0) {
			/* We have an explicit hole. */
			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx, 0, 0, 0,
						  key.offset, extent_end - 1);
		} else {
			/* We have a regular extent. */
			if (fieinfo->fi_extents_max) {
				ret = btrfs_is_data_extent_shared(inode,
								  disk_bytenr,
								  extent_gen,
								  backref_ctx);
				if (ret < 0)
					goto out_unlock;
				else if (ret > 0)
					flags |= FIEMAP_EXTENT_SHARED;
			}

			ret = emit_fiemap_extent(fieinfo, &cache, key.offset,
						 disk_bytenr + extent_offset,
						 extent_len, flags);
		}

		if (ret < 0) {
			goto out_unlock;
		} else if (ret > 0) {
			/* emit_fiemap_extent() told us to stop. */
			stopped = true;
			break;
		}

		prev_extent_end = extent_end;
next_item:
		if (fatal_signal_pending(current)) {
			ret = -EINTR;
			goto out_unlock;
		}

		ret = fiemap_next_leaf_item(inode, path);
		if (ret < 0) {
			goto out_unlock;
		} else if (ret > 0) {
			/* No more file extent items for this inode. */
			break;
		}
		cond_resched();
	}

check_eof_delalloc:
	if (!stopped && prev_extent_end < range_end) {
		ret = fiemap_process_hole(inode, fieinfo, &cache,
					  &delalloc_cached_state, backref_ctx,
					  0, 0, 0, prev_extent_end, range_end - 1);
		if (ret < 0)
			goto out_unlock;
		prev_extent_end = range_end;
	}

	if (cache.cached && cache.offset + cache.len >= last_extent_end) {
		const u64 i_size = i_size_read(&inode->vfs_inode);

		if (prev_extent_end < i_size) {
			u64 delalloc_start;
			u64 delalloc_end;
			bool delalloc;

			delalloc = btrfs_find_delalloc_in_range(inode,
								prev_extent_end,
								i_size - 1,
								&delalloc_cached_state,
								&delalloc_start,
								&delalloc_end);
			if (!delalloc)
				cache.flags |= FIEMAP_EXTENT_LAST;
		} else {
			cache.flags |= FIEMAP_EXTENT_LAST;
		}
	}

out_unlock:
	unlock_extent(&inode->io_tree, range_start, range_end, &cached_state);

	if (ret == BTRFS_FIEMAP_FLUSH_CACHE) {
		btrfs_release_path(path);
		ret = flush_fiemap_cache(fieinfo, &cache);
		if (ret)
			goto out;
		len -= cache.next_search_offset - start;
		start = cache.next_search_offset;
		goto restart;
	} else if (ret < 0) {
		goto out;
	}

	/*
	 * Must free the path before emitting to the fiemap buffer because we
	 * may have a non-cloned leaf and if the fiemap buffer is memory mapped
	 * to a file, a write into it (through btrfs_page_mkwrite()) may trigger
	 * waiting for an ordered extent that in order to complete needs to
	 * modify that leaf, therefore leading to a deadlock.
	 */
	btrfs_free_path(path);
	path = NULL;

	ret = flush_fiemap_cache(fieinfo, &cache);
	if (ret)
		goto out;

	ret = emit_last_fiemap_cache(fieinfo, &cache);
out:
	free_extent_state(delalloc_cached_state);
	kfree(cache.entries);
	btrfs_free_backref_share_ctx(backref_ctx);
	btrfs_free_path(path);
	return ret;
}

int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
		 u64 start, u64 len)
{
	struct btrfs_inode *btrfs_inode = BTRFS_I(inode);
	int ret;

	ret = fiemap_prep(inode, fieinfo, start, &len, 0);
	if (ret)
		return ret;

	/*
	 * fiemap_prep() called filemap_write_and_wait() for the whole possible
	 * file range (0 to LLONG_MAX), but that is not enough if we have
	 * compression enabled. The first filemap_fdatawrite_range() only kicks
	 * in the compression of data (in an async thread) and will return
	 * before the compression is done and writeback is started. A second
	 * filemap_fdatawrite_range() is needed to wait for the compression to
	 * complete and writeback to start. We also need to wait for ordered
	 * extents to complete, because our fiemap implementation uses mainly
	 * file extent items to list the extents, searching for extent maps
	 * only for file ranges with holes or prealloc extents to figure out
	 * if we have delalloc in those ranges.
	 */
	if (fieinfo->fi_flags & FIEMAP_FLAG_SYNC) {
		ret = btrfs_wait_ordered_range(btrfs_inode, 0, LLONG_MAX);
		if (ret)
			return ret;
	}

	btrfs_inode_lock(btrfs_inode, BTRFS_ILOCK_SHARED);

	/*
	 * We did an initial flush to avoid holding the inode's lock while
	 * triggering writeback and waiting for the completion of IO and ordered
	 * extents. Now after we locked the inode we do it again, because it's
	 * possible a new write may have happened in between those two steps.
	 */
	if (fieinfo->fi_flags & FIEMAP_FLAG_SYNC) {
		ret = btrfs_wait_ordered_range(btrfs_inode, 0, LLONG_MAX);
		if (ret) {
			btrfs_inode_unlock(btrfs_inode, BTRFS_ILOCK_SHARED);
			return ret;
		}
	}

	ret = extent_fiemap(btrfs_inode, fieinfo, start, len);
	btrfs_inode_unlock(btrfs_inode, BTRFS_ILOCK_SHARED);

	return ret;
}