[PATCH v2 1/3] xfs/178: don't fail when SCRATCH_DEV contains random xfs superblocks

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

When I added an fstests config for "RAID" striping (aka MKFS_OPTIONS='-d
su=128k,sw=4'), I suddenly started seeing this test fail sporadically
with:

--- /tmp/fstests/tests/xfs/178.out	2023-07-11 12:18:21.714970364 -0700
+++ /var/tmp/fstests/xfs/178.out.bad	2023-07-25 22:05:39.756000000 -0700
@@ -10,6 +10,20 @@ bad primary superblock - bad magic numbe

 attempting to find secondary superblock...
 found candidate secondary superblock...
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
+error reading superblock 1 -- seek to offset 584115421184 failed
+unable to verify superblock, continuing...
+found candidate secondary superblock...
 verified secondary superblock...
 writing modified primary superblock
 sb root inode INO inconsistent with calculated value INO

Eventually I tracked this down to a mis-interaction between the test,
xfs_repair, and the storage device.

If the device doesn't support discard, _scratch_mkfs won't zero the
entire disk to remove old dead superblocks that might have been written
by previous tests.  After we shatter the primary super, the xfs_repair
scanning code can still trip over those old supers when it goes looking
for secondary supers.

Most of the time it finds the actual AG 1 secondary super, but sometimes
it finds ghosts from previous formats.  When that happens, xfs_repair
will talk quite a bit about those failed secondaries, even if it
eventually finds an acceptable secondary sb and completes the repair.

Filter out the messages about secondary supers.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
v2: fix commit message to identify the problem in fstests, drop the
irrelevant mumbbling about SCSI UNMAP
---
 tests/xfs/178     |    9 ++++++++-
 tests/xfs/178.out |    2 --
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/tests/xfs/178 b/tests/xfs/178
index a65197cde3..fee1e92bf3 100755
--- a/tests/xfs/178
+++ b/tests/xfs/178
@@ -10,13 +10,20 @@
 . ./common/preamble
 _begin_fstest mkfs other auto
 
+filter_repair() {
+	_filter_repair | sed \
+		-e '/unable to verify superblock, continuing/d' \
+		-e '/found candidate secondary superblock/d' \
+		-e '/error reading superblock.*-- seek to offset/d'
+}
+
 # dd the 1st sector then repair
 _dd_repair_check()
 {
 	#dd first sector
 	dd if=/dev/zero of=$1 bs=$2 count=1 2>&1 | _filter_dd
 	#xfs_repair
-	_scratch_xfs_repair 2>&1 | _filter_repair
+	_scratch_xfs_repair 2>&1 | filter_repair
 	#check repair
 	if _check_scratch_fs; then
         	echo "repair passed"
diff --git a/tests/xfs/178.out b/tests/xfs/178.out
index 0bebe553eb..711e90cc26 100644
--- a/tests/xfs/178.out
+++ b/tests/xfs/178.out
@@ -9,7 +9,6 @@ Phase 1 - find and verify superblock...
 bad primary superblock - bad magic number !!!
 
 attempting to find secondary superblock...
-found candidate secondary superblock...
 verified secondary superblock...
 writing modified primary superblock
 sb root inode INO inconsistent with calculated value INO
@@ -45,7 +44,6 @@ Phase 1 - find and verify superblock...
 bad primary superblock - bad magic number !!!
 
 attempting to find secondary superblock...
-found candidate secondary superblock...
 verified secondary superblock...
 writing modified primary superblock
 sb root inode INO inconsistent with calculated value INO