[PATCH 1/1] btrfs: Align EOF length to block in extent_same

[Matt Robinson <git@nerdoftheherd.com>]

It is not currently possible to deduplicate the last block of files
whose size is not a multiple of the block size, as the btrfs_extent_same
ioctl returns -EINVAL if offset + size is greater than the file size or
is not aligned to the fs block size. This prevents btrfs from freeing up
the last extent in the file, causing gains from deduplication to be
smaller than expected.

To resolve this, allow unaligned offset + length values to be passed to
btrfs_ioctl_file_extent_same if offset + length = file size for both src
and dest.  This is implemented in the same way as in btrfs_ioctl_clone.

Signed-off-by: Matt Robinson <git@nerdoftheherd.com>
---
 fs/btrfs/ioctl.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d49fe8a..a407d8a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2871,14 +2871,16 @@ static int btrfs_cmp_data(struct inode *src, u64 loff, struct inode *dst,
 	return ret;
 }
 
-static int extent_same_check_offsets(struct inode *inode, u64 off, u64 len)
+static int extent_same_check_offsets(struct inode *inode, u64 off, u64 len,
+				     u64 len_aligned)
 {
 	u64 bs = BTRFS_I(inode)->root->fs_info->sb->s_blocksize;
 
 	if (off + len > inode->i_size || off + len < off)
 		return -EINVAL;
+
 	/* Check that we are block aligned - btrfs_clone() requires this */
-	if (!IS_ALIGNED(off, bs) || !IS_ALIGNED(off + len, bs))
+	if (!IS_ALIGNED(off, bs) || !IS_ALIGNED(off + len_aligned, bs))
 		return -EINVAL;
 
 	return 0;
@@ -2888,6 +2890,8 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 			     struct inode *dst, u64 dst_loff)
 {
 	int ret;
+	u64 len_aligned = len;
+	u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
 
 	/*
 	 * btrfs_clone() can't handle extents in the same file
@@ -2899,11 +2903,15 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 
 	btrfs_double_lock(src, loff, dst, dst_loff, len);
 
-	ret = extent_same_check_offsets(src, loff, len);
+	/* if we extend to both eofs, continue to block boundaries */
+	if (loff + len == src->i_size && dst_loff + len == dst->i_size)
+		len_aligned = ALIGN(src->i_size, bs) - loff;
+
+	ret = extent_same_check_offsets(src, loff, len, len_aligned);
 	if (ret)
 		goto out_unlock;
 
-	ret = extent_same_check_offsets(dst, dst_loff, len);
+	ret = extent_same_check_offsets(dst, dst_loff, len, len_aligned);
 	if (ret)
 		goto out_unlock;
 
@@ -2916,7 +2924,7 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 
 	ret = btrfs_cmp_data(src, loff, dst, dst_loff, len);
 	if (ret == 0)
-		ret = btrfs_clone(src, dst, loff, len, len, dst_loff);
+		ret = btrfs_clone(src, dst, loff, len, len_aligned, dst_loff);
 
 out_unlock:
 	btrfs_double_unlock(src, loff, dst, dst_loff, len);
@@ -3162,8 +3170,7 @@ static void clone_update_extent_map(struct inode *inode,
  * @inode: Inode to clone to
  * @off: Offset within source to start clone from
  * @olen: Original length, passed by user, of range to clone
- * @olen_aligned: Block-aligned value of olen, extent_same uses
- *               identical values here
+ * @olen_aligned: Block-aligned value of olen
  * @destoff: Offset within @inode to start clone
  */
 static int btrfs_clone(struct inode *src, struct inode *inode,
-- 
2.1.0