Re: [PATCH] common/xfs: wipe the XFS superblock of each AGs

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Sep 20, 2019 at 12:31:39PM +0800, Zorro Lang wrote:
> On Thu, Sep 19, 2019 at 07:48:36PM -0700, Darrick J. Wong wrote:
> > On Fri, Sep 20, 2019 at 09:52:11AM +0800, Yang Xu wrote:
> > > 
> > > 
> > > on 2019/09/19 23:00, Zorro Lang wrote:
> > > > xfs/030 always fails after d0e484ac699f ("check: wipe scratch devices
> > > > between tests") get merged.
> > > > 
> > > > Due to xfs/030 does a sized(100m) mkfs. Before we merge above commit,
> > > > mkfs.xfs detects an old primary superblock, it will write zeroes to
> > > > all superblocks before formatting the new filesystem. But this won't
> > > > be done if we wipe the first superblock(by merging above commit).
> > > > 
> > > > That means if we make a (smaller) sized xfs after wipefs, those *old*
> > > > superblocks which created by last time mkfs.xfs will be left on disk.
> > > > Then when we do xfs_repair, if xfs_repair can't find the first SB, it
> > > > will go to find those *old* SB at first. When it finds them,
> > > > everyting goes wrong.
> > > > 
> > > > So I try to get XFS AG geometry(by default) and then try to erase all
> > > > superblocks. Thanks Darrick J. Wong helped to analyze this issue.
> > > Feel free to add Reported-by.
> > > > 
> > > > Signed-off-by: Zorro Lang <zlang@redhat.com>
> > > > ---
> > > >   common/rc  |  4 ++++
> > > >   common/xfs | 23 +++++++++++++++++++++++
> > > >   2 files changed, 27 insertions(+)
> > > > 
> > > > diff --git a/common/rc b/common/rc
> > > > index 66c7fd4d..fe13f659 100644
> > > > --- a/common/rc
> > > > +++ b/common/rc
> > > > @@ -4048,6 +4048,10 @@ _try_wipe_scratch_devs()
> > > >   	for dev in $SCRATCH_DEV_POOL $SCRATCH_DEV $SCRATCH_LOGDEV $SCRATCH_RTDEV; do
> > > >   		test -b $dev && $WIPEFS_PROG -a $dev
> > > >   	done
> > > > +
> > > > +	if [ "$FSTYP" = "xfs" ];then
> > > > +		try_wipe_scratch_xfs
> > > I think we should add a simple comment for why we add it.
> > > 
> > > ps:_scratch_mkfs_xfs also can make case pass. We can use it and add comment.
> > > the  try_wipe_scratch_xfs method and the _scratch_mkfs_xfs method are all
> > > acceptable for me.
> > 
> > Yes, I suppose formatting and then wiping per below would also achieve
> > our means, but it would come at the extra cost of zeroing the log.  I'm
> > not too eager to increase xfstest runtime even more.
> > 
> > Hmmm, I wonder if xfs_db could just grow a 'wipe all superblocks'
> > command....
> 
> Haha, I was thinking about that too, and I tried this:
> --
> agc=`_scratch_xfs_get_sb_field agcount`
> wipe_xfs_cmd="$XFS_DB_PROG -x"
> for ((i=0; i<agc; i++)); do
> 	wipe_xfs_cmd="$wipe_xfs_cmd -c \"sb $i\" -c \"write -c magicnum 0x00000000\""
> done
> wipe_xfs_cmd="$wipe_xfs_cmd $SCRATCH_DEV"
> eval $wipe_xfs_cmd
> --
> 
> The only one problem about this, I think it's the max length of bash command:)

Yeah... I mean, the downside of all this is that a filesystme could have
thousands of AGs, though I don't imagine there are many people who set
up a 1PB array just to run xfstests ;)

--D

> Thanks,
> Zorro
> 
> > 
> > --D
> > 
> > > > +	fi
> > > >   }
> > > >   # Only run this on xfs if xfs_scrub is available and has the unicode checker
> > > > diff --git a/common/xfs b/common/xfs
> > > > index 1bce3c18..34516f82 100644
> > > > --- a/common/xfs
> > > > +++ b/common/xfs
> > > > @@ -884,3 +884,26 @@ _xfs_mount_agcount()
> > > >   {
> > > >   	$XFS_INFO_PROG "$1" | grep agcount= | sed -e 's/^.*agcount=\([0-9]*\),.*$/\1/g'
> > > >   }
> > > > +
> > > > +# wipe the superblock of each XFS AGs
> > > > +try_wipe_scratch_xfs()
> > > > +{
> > > > +	local tmp=`mktemp -u`
> > > > +
> > > > +	_scratch_mkfs_xfs -N 2>/dev/null | perl -ne '
> > > > +		if (/^meta-data=.*\s+agcount=(\d+), agsize=(\d+) blks/) {
> > > > +			print STDOUT "agcount=$1\nagsize=$2\n";
> > > > +		}
> > > > +		if (/^data\s+=\s+bsize=(\d+)\s/) {
> > > > +			print STDOUT "dbsize=$1\n";
> > > > +		}' > $tmp.mkfs
> > > > +
> > > > +	. $tmp.mkfs
> > > > +	if [ -n "$agcount" -a -n "$agsize" -a -n "$dbsize" ];then
> > > > +		for ((i = 0; i < agcount; i++)); do
> > > > +			$XFS_IO_PROG -c "pwrite $((i * dbsize * agsize)) $dbsize" \
> > > > +				$SCRATCH_DEV >/dev/null;
> > > > +		done
> > > > +       fi
> > > > +       rm -f $tmp.mkfs
> > > > +}
> > > > 
> > > 
> > >