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

[Dave Chinner <david@fromorbit.com>]

On Thu, Jun 16, 2016 at 10:10:09AM -0500, Eric Sandeen wrote:
> On 6/16/16 6:45 AM, Brian Foster wrote:
> > 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...
> 
> Yeah, that's surprising, it's been part of util-linux[-ng] on my RHEL &
> Fedora distros since 2009.

It's to do with dependencies against systemd and ensuring core
packages don't have systemd dependencies.  i.e. uuid-runtime has a
dependency on libsystemd because of the uuidd daemon that is used to
generate uuids. Hence it has to be packaged it separately so that
linux-util/libuuid packages do not require systemd to be installed
on the system.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com