1 files changed, 147 insertions, 1 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index fa4ef18b66b1..bd4d061c6e4d 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1664,8 +1664,154 @@ out:
 	return ret;
 }
 
+static int find_desired_extent(struct inode *inode, loff_t *offset, int origin)
+{
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct extent_map *em;
+	struct extent_state *cached_state = NULL;
+	u64 lockstart = *offset;
+	u64 lockend = i_size_read(inode);
+	u64 start = *offset;
+	u64 orig_start = *offset;
+	u64 len = i_size_read(inode);
+	u64 last_end = 0;
+	int ret = 0;
+
+	lockend = max_t(u64, root->sectorsize, lockend);
+	if (lockend <= lockstart)
+		lockend = lockstart + root->sectorsize;
+
+	len = lockend - lockstart + 1;
+
+	len = max_t(u64, len, root->sectorsize);
+	if (inode->i_size == 0)
+		return -ENXIO;
+
+	lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend, 0,
+			 &cached_state, GFP_NOFS);
+
+	/*
+	 * Delalloc is such a pain.  If we have a hole and we have pending
+	 * delalloc for a portion of the hole we will get back a hole that
+	 * exists for the entire range since it hasn't been actually written
+	 * yet.  So to take care of this case we need to look for an extent just
+	 * before the position we want in case there is outstanding delalloc
+	 * going on here.
+	 */
+	if (origin == SEEK_HOLE && start != 0) {
+		if (start <= root->sectorsize)
+			em = btrfs_get_extent_fiemap(inode, NULL, 0, 0,
+						     root->sectorsize, 0);
+		else
+			em = btrfs_get_extent_fiemap(inode, NULL, 0,
+						     start - root->sectorsize,
+						     root->sectorsize, 0);
+		if (IS_ERR(em)) {
+			ret = -ENXIO;
+			goto out;
+		}
+		last_end = em->start + em->len;
+		if (em->block_start == EXTENT_MAP_DELALLOC)
+			last_end = min_t(u64, last_end, inode->i_size);
+		free_extent_map(em);
+	}
+
+	while (1) {
+		em = btrfs_get_extent_fiemap(inode, NULL, 0, start, len, 0);
+		if (IS_ERR(em)) {
+			ret = -ENXIO;
+			break;
+		}
+
+		if (em->block_start == EXTENT_MAP_HOLE) {
+			if (test_bit(EXTENT_FLAG_VACANCY, &em->flags)) {
+				if (last_end <= orig_start) {
+					free_extent_map(em);
+					ret = -ENXIO;
+					break;
+				}
+			}
+
+			if (origin == SEEK_HOLE) {
+				*offset = start;
+				free_extent_map(em);
+				break;
+			}
+		} else {
+			if (origin == SEEK_DATA) {
+				if (em->block_start == EXTENT_MAP_DELALLOC) {
+					if (start >= inode->i_size) {
+						free_extent_map(em);
+						ret = -ENXIO;
+						break;
+					}
+				}
+
+				*offset = start;
+				free_extent_map(em);
+				break;
+			}
+		}
+
+		start = em->start + em->len;
+		last_end = em->start + em->len;
+
+		if (em->block_start == EXTENT_MAP_DELALLOC)
+			last_end = min_t(u64, last_end, inode->i_size);
+
+		if (test_bit(EXTENT_FLAG_VACANCY, &em->flags)) {
+			free_extent_map(em);
+			ret = -ENXIO;
+			break;
+		}
+		free_extent_map(em);
+		cond_resched();
+	}
+	if (!ret)
+		*offset = min(*offset, inode->i_size);
+out:
+	unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
+			     &cached_state, GFP_NOFS);
+	return ret;
+}
+
+static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int origin)
+{
+	struct inode *inode = file->f_mapping->host;
+	int ret;
+
+	mutex_lock(&inode->i_mutex);
+	switch (origin) {
+	case SEEK_END:
+	case SEEK_CUR:
+		offset = generic_file_llseek_unlocked(file, offset, origin);
+		goto out;
+	case SEEK_DATA:
+	case SEEK_HOLE:
+		ret = find_desired_extent(inode, &offset, origin);
+		if (ret) {
+			mutex_unlock(&inode->i_mutex);
+			return ret;
+		}
+	}
+
+	if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET))
+		return -EINVAL;
+	if (offset > inode->i_sb->s_maxbytes)
+		return -EINVAL;
+
+	/* Special lock needed here? */
+	if (offset != file->f_pos) {
+		file->f_pos = offset;
+		file->f_version = 0;
+	}
+out:
+	mutex_unlock(&inode->i_mutex);
+	return offset;
+}
+
 const struct file_operations btrfs_file_operations = {
-	.llseek		= generic_file_llseek,
+	.llseek		= btrfs_file_llseek,
 	.read		= do_sync_read,
 	.write		= do_sync_write,
 	.aio_read       = generic_file_aio_read,