Re: xfs/420 and xfs/421: don't disturb unwritten status with md5sum

[Eryu Guan <guaneryu@gmail.com>]

On Mon, Feb 18, 2019 at 10:19:51AM +0100, Christoph Hellwig wrote:
> The way we decided if an unwritten extent is considered a hole or data
> is by checking if the page and/or blocks are marked uptodate, that is
> contain valid data in the page cache.
> 
> xfs/420 and xfs/421 try to exercise SEEK_HOLE / SEEK_DATA in the
> presence of cowextsize preallocations over holes in the data fork.  The
> current XFS code never actually uses those for buffer writes, but a
> pending patch changes that.  For SEEK_HOLE / SEEK_DATA to work properly
> in that case we also need to look at the COW fork in their
> implementations and thus have to rely on the unwritten extent page cache
> probing.  But the tests for it ensure we do have valid data in the
> pagecache by calling md5sum on the test files, and thus reading their
> contents (including the zero-filled holes) in, and thus making them
> all valid data.
> 
> Fix that by dropping the page cache content after the md5sum calls.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Hi Darrick, would you please help review this version of the fix as
well? I basically have no idea about the implementation of the "pending
patch" and what it changes.. Thanks a lot!

Eryu

> ---
>  tests/xfs/420 | 6 ++++++
>  tests/xfs/421 | 6 ++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/tests/xfs/420 b/tests/xfs/420
> index a083a12b..34199637 100755
> --- a/tests/xfs/420
> +++ b/tests/xfs/420
> @@ -83,6 +83,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "CoW the shared part then write into the empty part" | tee -a $seqres.full
>  $XFS_IO_PROG -c "cowextsize" $testdir/file1 >> $seqres.full
> @@ -106,6 +108,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "sync filesystem" | tee -a $seqres.full
>  sync
> @@ -123,6 +127,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "Remount" | tee -a $seqres.full
>  _scratch_cycle_mount
> diff --git a/tests/xfs/421 b/tests/xfs/421
> index a2734aba..374389bd 100755
> --- a/tests/xfs/421
> +++ b/tests/xfs/421
> @@ -83,6 +83,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "CoW the shared part then write into the empty part" | tee -a $seqres.full
>  $XFS_IO_PROG -c "cowextsize" $testdir/file1 >> $seqres.full
> @@ -106,6 +108,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "sync filesystem" | tee -a $seqres.full
>  sync
> @@ -123,6 +127,8 @@ echo "Compare files"
>  md5sum $testdir/file1 | _filter_scratch
>  md5sum $testdir/file2 | _filter_scratch
>  md5sum $testdir/file3 | _filter_scratch
> +# drop caches to make sure the page cache for the unwritten extents is clean
> +echo 1 > /proc/sys/vm/drop_caches
>  
>  echo "Remount" | tee -a $seqres.full
>  _scratch_cycle_mount
> -- 
> 2.20.1
>