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

[Brian Foster <bfoster@redhat.com>]

On Thu, Jun 16, 2016 at 11:13:49AM +1000, Dave Chinner wrote:
> 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).
> 

Eryu pointed this on on v1 of the test but I didn't think it necessary
as it's part of a standard package on fedora. I guess that's not true
for other distros. I'll post something to fix it up...

Brian

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
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