[PATCH v2] fstests: btrfs/315: fix golden output mismatch caused by newer util-linux

[Qu Wenruo <wqu@suse.com>]

[BUG]
With util-linux v2.41.0 and newer, test case btrfs/315 will fail like
the following:

btrfs/315 1s ... - output mismatch (see /home/adam/xfstests-dev/results//btrfs/315.out.bad)
    --- tests/btrfs/315.out	2025-04-24 15:31:28.684112371 +0930
    +++ /home/adam/xfstests-dev/results//btrfs/315.out.bad	2025-04-24 15:31:31.854883557 +0930
    @@ -1,7 +1,7 @@
     QA output created by 315
     ---- seed_device_must_fail ----
     mount: SCRATCH_MNT: WARNING: source write-protected, mounted read-only.
    -mount: TEST_DIR/315/tempfsid_mnt:  system call failed: File exists.
    +mount: TEST_DIR/315/tempfsid_mnt: () failed: File exists.
     ---- device_add_must_fail ----
     wrote 9000/9000 bytes at offset 0

[CAUSE]

With util-linux v2.41.0, the mount failure error message changed to the following:

  mount: /mnt/test/315/tempfsid_mnt: fsconfig() failed: File exists.

Thus the existing filter only striped the "fsconfig" part, leaving the
"()" without changing it to " system call".

[FIX]
The test case is doomed in day one by using a local filter, which
requires stupid catch-up game against util-linux.

Meanwhile we already have a much better filter, _filter_error_mount().
That helper can already handle the newer v2.41 output.

Let's use the superior common filter and update the golden output to:

  mount: File exists.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Remove the cursed local filter and use the generic one instead
---
 tests/btrfs/315     | 22 ++--------------------
 tests/btrfs/315.out |  2 +-
 2 files changed, 3 insertions(+), 21 deletions(-)

diff --git a/tests/btrfs/315 b/tests/btrfs/315
index e6589abe..9071e152 100755
--- a/tests/btrfs/315
+++ b/tests/btrfs/315
@@ -19,6 +19,7 @@ _cleanup()
 }
 
 . ./common/filter.btrfs
+. ./common/filter
 
 _require_scratch_dev_pool 3
 _require_btrfs_fs_feature temp_fsid
@@ -28,25 +29,6 @@ _scratch_dev_pool_get 3
 # mount point for the tempfsid device
 tempfsid_mnt=$TEST_DIR/$seq/tempfsid_mnt
 
-_filter_mount_error()
-{
-	# There are two different errors that occur at the output when
-	# mounting fails; as shown below, pick out the common part. And,
-	# remove the dmesg line.
-
-	# mount: <mnt-point>: mount(2) system call failed: File exists.
-
-	# mount: <mnt-point>: fsconfig system call failed: File exists.
-	# dmesg(1) may have more information after failed mount system call.
-
-	# For util-linux v2.4 and later:
-	# mount: <mountpoint>: mount system call failed: File exists.
-
-	grep -v dmesg | _filter_test_dir | \
-		sed -e "s/mount(2)\|fsconfig//g" \
-		    -e "s/mount\( system call failed:\)/\1/"
-}
-
 seed_device_must_fail()
 {
 	echo ---- $FUNCNAME ----
@@ -57,7 +39,7 @@ seed_device_must_fail()
 	$BTRFS_TUNE_PROG -S 1 ${SCRATCH_DEV_NAME[1]}
 
 	_scratch_mount 2>&1 | _filter_scratch
-	_mount ${SCRATCH_DEV_NAME[1]} ${tempfsid_mnt} 2>&1 | _filter_mount_error
+	_mount ${SCRATCH_DEV_NAME[1]} ${tempfsid_mnt} 2>&1 | _filter_error_mount
 }
 
 device_add_must_fail()
diff --git a/tests/btrfs/315.out b/tests/btrfs/315.out
index 3ea7a35a..ae77d4fd 100644
--- a/tests/btrfs/315.out
+++ b/tests/btrfs/315.out
@@ -1,7 +1,7 @@
 QA output created by 315
 ---- seed_device_must_fail ----
 mount: SCRATCH_MNT: WARNING: source write-protected, mounted read-only.
-mount: TEST_DIR/315/tempfsid_mnt:  system call failed: File exists.
+mount: File exists
 ---- device_add_must_fail ----
 wrote 9000/9000 bytes at offset 0
 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-- 
2.49.0