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

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

On Thu, Sep 19, 2019 at 11:00:24PM +0800, 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.

One thing missing from this patch -- if the test formatted the scratch
device with non-default geometry, the backup superblocks from that
filesystem will not be erased.  Going back to my example from the email
thread, if the scratch disk has:

  SB0 [16M zeroes] SB1 [16M zeroes] <4 more AGs> <zeroes from 100M to 1G> \
      SB'1 [1G space] SB'2 [1G space] SB'3 [1G space]

Where SB[0-5] are the ones written by xfs/030 and SB'[1-3] were written
by a previous test that did the default scratch device mkfs, then this
patch will wipe out SB'[1-3] and SB0:

  000 [16M zeroes] SB1 [16M zeroes] <4 more AGs> <zeroes from 100M to 1G> \
      0000 [1G space] 0000 [1G space] 0000 [1G space]

But that still leaves SB[1-5] which xfs_repair could stumble over later.
For example, if the next test to be run formats a filesystem with 24MB
AGs (instead of 16) and zaps the superblock, then repair will eventually
try a linear scan looking for superblocks and find the ones from the
16MB filesystem first.

There isn't a sequence of tests that do this, but so long as we're
fixing this we might as well zap as much as we can.  So I propose adding
to try_wipe_scratch_xfs() the following:

	dbsize=
	_scratch_xfs_db -c 'sb 0' -c 'p blocksize agblocks agcount' 2>&1 | \
		sed -e 's/ = /=/g' -e 's/blocksize/dbsize/g' \
		    -e 's/agblocks/agsize/g' > $tmp.mkfs
	. $tmp.mkfs

and then repeat the for loop.  If there isn't a filesystem then
$tmp.mkfs will be an empty file and the loop won't run.

> 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.
> 
> 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
> +	fi

We probably ought to delegate all wiping to try_wipe_scratch_xfs, i.e.:

	test -b $dev || continue
	case "$FSTYP" in
	"xfs")
		_try_wipe_scratch_xfs
		;;
	*)
		$WIPEFS_PROG -a $dev
		;;
	esac

and add the WIPEFS_PROG call to _try_wipe_scratch_xfs.

>  }
>  
>  # 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()

Common helper functions should start with a '_'

> +{
> +	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

Add code as discussed above.

--D

> +}
> -- 
> 2.20.1
>