Re: [PATCH v2] xfstests: xfs discontiguous multi-block buffer logging test

[Dave Chinner <david@fromorbit.com>]

On Thu, Jun 02, 2016 at 09:10:01AM -0400, Brian Foster wrote:
> XFS had a bug in the multi-block buffer logging code that caused a NULL
> lv panic at log push time due to invalid regions being set in the buffer
> log format bitmap. This was demonstrated by modifying a multi-block
> directory buffer in a manner that only logs regions beyond the first
> FSB-sized mapping of the buffer.
> 
> To recreate these conditions, this test fragments free space and
> populates several directories with enough entries to require
> discontiguous multi-block buffers. To recreate the problem, we remove
> entries from the tail end of the directory and fsync to flush the log.
> 
> Note that this test causes a panic on kernels affected by the bug. As
> such, it is included in the 'dangerous' group. The bug is resolved by
> kernel commit a3916e528b91 ("xfs: fix broken multi-fsb buffer logging").
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
.....
> +# Create a small fs with a large directory block size. We want to fill up the fs
> +# quickly and then create multi-fsb dirblocks over fragmented free space.
> +_scratch_mkfs_xfs -d size=20m -n size=64k >> $seqres.full 2>&1
> +_scratch_mount
> +
> +# Fill a source directory with many largish-named files. 1k uuid-named entries
> +# sufficiently populates a 64k directory block.
> +mkdir $SCRATCH_MNT/src
> +for i in $(seq 0 1023); do
> +	touch $SCRATCH_MNT/src/`uuidgen`
> +done

What's 'uuidgen'? Not installed on my test systems, so this needs
a requires check, I think....

Hmmm - looks like a separate package is needed on debian systems:
uuid-runtime. Can you send a followup patch that adds the necesary
checks to this test and added the above package to the iniitial list
in the README file (for ubunutu, I know, but the package name will
be the same).

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com