[PATCH] fstests: btrfs/220: fix the test failure due to new default mount option

[Qu Wenruo <wqu@suse.com>]

[BUG]
The latest misc-next tree will make test case btrfs/220 fail with the
following error messages:

btrfs/220 15s ... - output mismatch (see ~/xfstests/results//btrfs/220.out.bad)
    --- tests/btrfs/220.out	2022-05-11 09:55:30.749999997 +0800
    +++ ~/xfstests/results//btrfs/220.out.bad	2022-12-09 13:57:23.706666671 +0800
    @@ -1,2 +1,5 @@
     QA output created by 220
    +Unexepcted mount options, checking for 'rw,relatime,discard=async,space_cache=v2,subvolid=5,subvol=/' in 'rw,relatime,space_cache=v2,subvolid=5,subvol=/' using 'nodiscard'
    +Unexepcted mount options, checking for 'rw,relatime,discard=async,space_cache=v2,subvolid=5,subvol=/' in 'rw,relatime,space_cache=v2,subvolid=5,subvol=/' using 'nodiscard'
    +Unexepcted mount options, checking for 'rw,relatime,discard=async,space_cache=v2,subvolid=5,subvol=/' in 'rw,relatime,space_cache=v2,subvolid=5,subvol=/' using 'nodiscard'
     Silence is golden
    ...
    (Run 'diff -u ~/xfstests/tests/btrfs/220.out ~/xfstests/results//btrfs/220.out.bad'  to see the entire diff)
Ran: btrfs/220
Failures: btrfs/220
Failed 1 of 1 tests

[CAUSE]
Since patch "btrfs: auto enable discard=async when possible", which is
already in the maintainer's tree for next merge window, btrfs will
automatically enable asynchronous discard for devices which supports
discard.

This makes our $DEFAULT_OPTS to have "discard=async" in it.

While for "nodiscard" mount option, we will completely disable all
discard, causing the above mismatch.

[FIX]
Fix it by introducing $DEFAULT_NODISCARD_OPTS specifically for
"nodiscard" mount option.

If async discard is not enabled by default, $DEFAULT_NODISCARD_OPTS will
be the same as $DEFAULT_OPTS, thus everything would work as usual.

If async discard is enabled by default, $DEFAULT_NODISCARD_OPTS will
have that removed, so for "nodiscard" we can use $DEFAULT_NODISCARD_OPTS
as expected mount options.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 tests/btrfs/220 | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tests/btrfs/220 b/tests/btrfs/220
index 4d94ccd6..30ca06f6 100755
--- a/tests/btrfs/220
+++ b/tests/btrfs/220
@@ -280,10 +280,10 @@ test_revertible_options()
 	if [ "$enable_discard_sync" = true ]; then
 		test_roundtrip_mount "discard" "discard" "discard=sync" "discard"
 		test_roundtrip_mount "discard=async" "discard=async" "discard=sync" "discard"
-		test_roundtrip_mount "discard=sync" "discard" "nodiscard" "$DEFAULT_OPTS"
+		test_roundtrip_mount "discard=sync" "discard" "nodiscard" "$DEFAULT_NODISCARD_OPTS"
 	else
 		test_roundtrip_mount "discard" "discard" "discard" "discard"
-		test_roundtrip_mount "discard" "discard" "nodiscard" "$DEFAULT_OPTS"
+		test_roundtrip_mount "discard" "discard" "nodiscard" "$DEFAULT_NODISCARD_OPTS"
 	fi
 
 	test_roundtrip_mount "enospc_debug" "enospc_debug" "noenospc_debug" "$DEFAULT_OPTS"
@@ -344,6 +344,12 @@ _scratch_mount
 DEFAULT_OPTS=$(cat /proc/self/mounts | grep $SCRATCH_MNT | \
 		$AWK_PROG '{ print $4 }')
 
+# Since 63a7cb130718 ("btrfs: auto enable discard=async when possible"),
+# "discard=async" will be automatically enabled if the device supports.
+# This can screw up our test against nodiscard options, thus remove the
+# default "discard=async" mount option for "nodiscard" tests.
+DEFAULT_NODISCARD_OPTS=$(echo -n "$DEFAULT_OPTS" | $SED_PROG 's/,discard=async//')
+
 $BTRFS_UTIL_PROG subvolume create "$SCRATCH_MNT/vol1" > /dev/null
 touch "$SCRATCH_MNT/vol1/file.txt"
 _scratch_unmount
-- 
2.38.0