From: Robbie Ko <robbi...@synology.com>
[BUG]
fm_mapped_extents is not correct when fm_extent_count is 0
Like:
# mount /dev/vdb5 /mnt/btrfs
# dd if=/dev/zero bs=16K count=4 oflag=dsync of=/mnt/btrfs/file
# xfs_io -c "fiemap -v" /mnt/btrfs/file
/mnt/btrfs/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 25088..25215 128 0x1
When user space wants to get the number of file extents,
set fm_extent_count to 0 to run fiemap and then read fm_mapped_extents.
In the above example, fiemap will return with fm_mapped_extents set to 4,
but it should be 1 since there's only one entry in the output.
[REASON]
The problem seems to be that disko is only set if
fieinfo->fi_extents_max is set. And this member is initialized, in the
generic ioctl_fiemap function, to the value of used-passed
fm_extent_count. So when the user passes 0 then fi_extent_max is also
set to zero and this causes btrfs to not initialize disko at all.
Eventually this leads emit_fiemap_extent being called with a bogus
'phys' argument preventing proper fiemap entries merging.
[FIX]
Move the disko initialization earlier in extent_fiemap making it
independent of user-passed arguments, allowing emit_fiemap_extent to
properly handle consecutive extent entries.
Signed-off-by: Robbie Ko <robbi...@synology.com>
---
V2:
fix comments.
fs/btrfs/extent_io.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 012d638..066b6df 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4567,7 +4567,7 @@ int extent_fiemap(struct inode *inode, struct
fiemap_extent_info *fieinfo,
offset_in_extent = em_start - em->start;
em_end = extent_map_end(em);
em_len = em_end - em_start;
- disko = 0;
+ disko = em->block_start + offset_in_extent;
flags = 0;
/*
@@ -4590,8 +4590,6 @@ int extent_fiemap(struct inode *inode, struct
fiemap_extent_info *fieinfo,
u64 bytenr = em->block_start -
(em->start - em->orig_start);
- disko = em->block_start + offset_in_extent;
-
/*
* As btrfs supports shared space, this information
* can be exported to userspace tools via
--
1.9.1
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