[PATCH 1/2] generic/251: don't snapshot $here during a test

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

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

Zorro complained that the next patch caused him a regression:

generic/251 249s ... [failed, exit status 1]- output mismatch (see /root/git/xfstests/results//generic/251.out.bad)
    --- tests/generic/251.out   2022-04-29 23:07:23.263498297 +0800
    +++ /root/git/xfstests/results//generic/251.out.bad 2023-10-22 14:17:07.248059405 +0800
    @@ -1,2 +1,5 @@
     QA output created by 251
     Running the test: done.
    +5838a5839
    +> aa60581221897d3d7dd60458e1cca2fa  ./results/generic/251.full
    +!!!Checksums has changed - Filesystem possibly corrupted!!!\n
    ...
    (Run 'diff -u /root/git/xfstests/tests/generic/251.out /root/git/xfstests/results//generic/251.out.bad'  to see the entire diff)
Ran: generic/251
Failures: generic/251
Failed 1 of 1 tests

The next patch writes some debugging information into $seqres.full,
which is a file underneat $RESULT_BASE.  If the test operator does not
set RESULT_BASE, it will be set to a subdir of $here by default.  Since
this test also snapshots the contents of $here before starting its loop,
any logging to $seqres.full on such a system will cause the post-copy
checksum to fail due to a mismatch.

Fix all this by copying $here to $SCRATCH_DEV and checksumming the copy
before the FITRIM stress test begins to avoid problems with $seqres.full.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 tests/generic/251 |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/generic/251 b/tests/generic/251
index 8ee74980cc..3b807df5fa 100755
--- a/tests/generic/251
+++ b/tests/generic/251
@@ -130,7 +130,13 @@ function run_process() {
 }
 
 nproc=20
-content=$here
+
+# Copy $here to the scratch fs and make coipes of the replica.  The fstests
+# output (and hence $seqres.full) could be in $here, so we need to snapshot
+# $here before computing file checksums.
+content=$SCRATCH_MNT/orig
+mkdir -p $content
+cp -axT $here/ $content/
 
 mkdir -p $tmp