[PATCH U-BOOT 1/3] btrfs: fix offset within btrfs_read_extent_reg()

[Dominique Martinet]

From: Dominique Martinet <dominique.martinet at atmark-techno.com>

btrfs_read_extent_reg correctly computed the extent offset in the
BTRFS_COMPRESS_NONE case, but did not account for the 'offset - key.offset'
part correctly in the compressed case, making the function read
incorrect data.

In the case I examined, the last 4k of a file was corrupted and
contained data from a few blocks prior:
btrfs_file_read()
 -> btrfs_read_extent_reg
    (aligned part loop from 0x40480000 to 0x40ba0000, 128KB at a time)
     last read had 0x4000 bytes in extent, but aligned_end - cur limited
     the read to 0x3000 (offset 0x720000)
 -> read_and_truncate_page
   -> btrfs_read_extent_reg
      reading the last 0x1000 bytes from offset 0x73000 (end of the
      previous 0x4000) into 0x40ba3000
      here key.offset = 0x70000 so we need to use it to recover the
      0x3000 offset.

Confirmed by checking data, before patch:
u-boot=> mmc load 1:1 $loadaddr boot/uImage
u-boot=> md 0x40ba0000
40ba0000: c0232ff8 c0c722cb 030e94be bf10000c    ./#.."..........
u-boot=> md 0x40ba3000
40ba3000: c0232ff8 c0c722cb 030e94be bf10000c    ./#.."..........

After patch (also confirmed with data read from linux):
u-boot=> md 0x40ba3000
40ba3000: 64cc9f03 81142256 6910000c 0c03483c    ...dV".....i<H..

Note that the code previously (before commit e3427184f38a ("fs: btrfs:
Implement btrfs_file_read()")) did not split that read in two, so
this is a regression.

Fixes: a26a6bedafcf ("fs: btrfs: Introduce btrfs_read_extent_inline() and btrfs_read_extent_reg()")
Signed-off-by: Dominique Martinet <dominique.martinet at atmark-techno.com>
---
 fs/btrfs/inode.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 40025662f250..3d6e39e6544d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -443,6 +443,8 @@ int btrfs_read_extent_reg(struct btrfs_path *path,
 	       IS_ALIGNED(len, fs_info->sectorsize));
 	ASSERT(offset >= key.offset &&
 	       offset + len <= key.offset + extent_num_bytes);
+	/* offset is now offset within extent */
+	offset = btrfs_file_extent_offset(leaf, fi) + offset - key.offset;
 
 	/* Preallocated or hole , fill @dest with zero */
 	if (btrfs_file_extent_type(leaf, fi) == BTRFS_FILE_EXTENT_PREALLOC ||
@@ -454,9 +456,7 @@ int btrfs_read_extent_reg(struct btrfs_path *path,
 	if (btrfs_file_extent_compression(leaf, fi) == BTRFS_COMPRESS_NONE) {
 		u64 logical;
 
-		logical = btrfs_file_extent_disk_bytenr(leaf, fi) +
-			  btrfs_file_extent_offset(leaf, fi) +
-			  offset - key.offset;
+		logical = btrfs_file_extent_disk_bytenr(leaf, fi) + offset;
 		read = len;
 
 		num_copies = btrfs_num_copies(fs_info, logical, len);
@@ -511,7 +511,7 @@ int btrfs_read_extent_reg(struct btrfs_path *path,
 	if (ret < dsize)
 		memset(dbuf + ret, 0, dsize - ret);
 	/* Then copy the needed part */
-	memcpy(dest, dbuf + btrfs_file_extent_offset(leaf, fi), len);
+	memcpy(dest, dbuf + offset, len);
 	ret = len;
 out:
 	free(cbuf);

-- 
2.39.2