[v2] Btrfs: fix physical offset reported by fiemap for inline extents

Commit Message

Filipe Manana June 20, 2018, 9:02 a.m. UTC

From: Filipe Manana <[e-mail]>

Commit 9d311e11fc1f ("Btrfs: fiemap: pass correct bytenr when
fm_extent_count is zero") introduced a regression where we no longer
report 0 as the physical offset for inline extents (and other extents
with a special block_start value). This is because it always sets the
variable used to report the physical offset ("disko") as em->block_start
plus some offset, and em->block_start has the value 18446744073709551614
((u64) -2) for inline extents.

This made the btrfs test 004 (from fstests) often fail, for example, for
a file with an inline extent we have the following items in the subvolume
tree:

    item 101 key (418 INODE_ITEM 0) itemoff 11029 itemsize 160
           generation 25 transid 38 size 1525 nbytes 1525
           block group 0 mode 100666 links 1 uid 0 gid 0 rdev 0
           sequence 0 flags 0x2(none)
           atime 1529342058.461891730 (2018-06-18 18:14:18)
           ctime 1529342058.461891730 (2018-06-18 18:14:18)
           mtime 1529342058.461891730 (2018-06-18 18:14:18)
           otime 1529342055.869892885 (2018-06-18 18:14:15)
    item 102 key (418 INODE_REF 264) itemoff 11016 itemsize 13
           index 25 namelen 3 name: fc7
    item 103 key (418 EXTENT_DATA 0) itemoff 9470 itemsize 1546
           generation 38 type 0 (inline)
           inline extent data size 1525 ram_bytes 1525 compression 0 (none)

Then when test 004 invoked fiemap against the file it got a non-zero
physical offset:

 $ filefrag -v /mnt/p0/d4/d7/fc7
 Filesystem type is: 9123683e
 File size of /mnt/p0/d4/d7/fc7 is 1525 (1 block of 4096 bytes)
  ext:     logical_offset:        physical_offset: length:   expected: flags:
    0:        0..    4095: 18446744073709551614..      4093:   4096:             last,not_aligned,inline,eof
 /mnt/p0/d4/d7/fc7: 1 extent found

This resulted in the test failing like this:

btrfs/004 49s ... [failed, exit status 1]- output mismatch (see /home/fdmanana/git/hub/xfstests/results//btrfs/004.out.bad)
    --- tests/btrfs/004.out	2016-08-23 10:17:35.027012095 +0100
    +++ /home/fdmanana/git/hub/xfstests/results//btrfs/004.out.bad	2018-06-18 18:15:02.385872155 +0100
    @@ -1,3 +1,10 @@
     QA output created by 004
     *** test backref walking
    -*** done
    +./tests/btrfs/004: line 227: [: 7.55578637259143e+22: integer expression expected
    +ERROR: 7.55578637259143e+22 is not a valid numeric value.
    +unexpected output from
    +	/home/fdmanana/git/hub/btrfs-progs/btrfs inspect-internal logical-resolve -s 65536 -P 7.55578637259143e+22 /home/fdmanana/btrfs-tests/scratch_1
    ...
    (Run 'diff -u tests/btrfs/004.out /home/fdmanana/git/hub/xfstests/results//btrfs/004.out.bad'  to see the entire diff)
Ran: btrfs/004

The large number in scientific notation reported as an invalid numeric
value is the result from the filter passed to perl which multiplies the
physical offset by the block size reported by fiemap.

So fix this by ensuring the physical offset is always set to 0 when we
are processing an extent with a special block_start value.

Fixes: 9d311e11fc1f ("Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero")
Signed-off-by: Filipe Manana <[e-mail]>
---

v2: Set the physical offset to 0 for other extent maps with a special
    block_start value as well.

 fs/btrfs/extent_io.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Nikolay Borisov June 25, 2018, 9:36 a.m. UTC | #1

On 20.06.2018 12:02, [e-mail] wrote:
> From: Filipe Manana <[e-mail]>
> 
<snip>

> So fix this by ensuring the physical offset is always set to 0 when we
> are processing an extent with a special block_start value.
> 
> Fixes: 9d311e11fc1f ("Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero")
> Signed-off-by: Filipe Manana <[e-mail]>

At first I was "wtf" since I had missed the u64 cast. After realising
that the constants are in fact always parsed as positive numbers then it
makes sense.

Reviewed-by: Nikolay Borisov <[e-mail]>

> ---
> 
> v2: Set the physical offset to 0 for other extent maps with a special
>     block_start value as well.
> 
>  fs/btrfs/extent_io.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 8e4a7cdbc9f5..1aa91d57404a 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4545,8 +4545,11 @@ 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 = em->block_start + offset_in_extent;
>  		flags = 0;
> +		if (em->block_start < EXTENT_MAP_LAST_BYTE)
> +			disko = em->block_start + offset_in_extent;
> +		else
> +			disko = 0;
>  
>  		/*
>  		 * bump off for our next call to get_extent
> 
--
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Patch

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 8e4a7cdbc9f5..1aa91d57404a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4545,8 +4545,11 @@  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 = em->block_start + offset_in_extent;
 		flags = 0;
+		if (em->block_start < EXTENT_MAP_LAST_BYTE)
+			disko = em->block_start + offset_in_extent;
+		else
+			disko = 0;
 
 		/*
 		 * bump off for our next call to get_extent