[PATCH] fstests: generic/362: remove the old file to reflect new mount options

[HIDDEN BUG]
There is a btrfs bug that will only trigger on newly formated TEST_DEV,
with mount option "nodatasum":

 FSTYP         -- btrfs
 PLATFORM      -- Linux/x86_64 btrfs-vm 7.1.0-rc4-custom+ #381 SMP PREEMPT_DYNAMIC Tue May 26 10:47:14 ACST 2026
 MKFS_OPTIONS  -- -O bgt -K /dev/mapper/test-scratch1
 MOUNT_OPTIONS -- -o nodatasum /dev/mapper/test-scratch1 /mnt/scratch

 generic/362  0s ... - output mismatch (see /home/adam/xfstests/results//generic/362.out.bad)
     --- tests/generic/362.out	2024-08-24 15:31:37.200000000 +0930
     +++ /home/adam/xfstests/results//generic/362.out.bad	2026-05-26 16:24:40.201201849 +0930
     @@ -1,2 +1,3 @@
      QA output created by 362
     +First write failed: Input/output error
      Silence is golden
     ...
     (Run 'diff -u /home/adam/xfstests/tests/generic/362.out /home/adam/xfstests/results//generic/362.out.bad'  to see the entire diff)

But if one has formated TEST_DEV, run test with default mount option,
then change the mount option to "nodatasum", the test will not fail
anymore:

 FSTYP         -- btrfs
 PLATFORM      -- Linux/x86_64 btrfs-vm 7.1.0-rc4-custom+ #381 SMP PREEMPT_DYNAMIC Tue May 26 10:47:14 ACST 2026
 MKFS_OPTIONS  -- -O bgt -K /dev/mapper/test-scratch1
 MOUNT_OPTIONS -- /dev/mapper/test-scratch1 /mnt/scratch

 generic/362  0s ...  0s
 Ran: generic/362
 Passed all 1 tests

 FSTYP         -- btrfs
 PLATFORM      -- Linux/x86_64 btrfs-vm 7.1.0-rc4-custom+ #381 SMP PREEMPT_DYNAMIC Tue May 26 10:47:14 ACST 2026
 MKFS_OPTIONS  -- -O bgt -K /dev/mapper/test-scratch1
 MOUNT_OPTIONS -- -o nodatasum /dev/mapper/test-scratch1 /mnt/scratch

 generic/362  0s ...  0s
 Ran: generic/362
 Passed all 1 tests

[CAUSE]
Btrfs' nodatasum mount option only affect new files, but the test case
itself is using TEST_DEV, and never delete the file
"$TEST_DIR/dio-append-buf-fault"

So if the file is created with default mount option, then all later
"nodatasum" mount option will not affect that file, thus hide the test
failure.

[FIX]
Always delete the target file "$TEST_DIR/dio-append-buf-fault" before
running dio-append-buf-fault command.

So that the new target file is always newly created and will follow
btrfs' new mount option and expose the failure for nodatasum.

Signed-off-by: Qu Wenruo <[email protected]>
---
I'm already looking into the test failure, because it's mostly hidden by
the btrfs' falling back to buffered IO behavior.

With the incoming IOMAP_DIO_BOUNCE usage inside btrfs, it will expose
the failure unconditionally.
---
 tests/generic/362 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/generic/362 b/tests/generic/362
index 0cfaa726..86191e57 100755
--- a/tests/generic/362
+++ b/tests/generic/362
@@ -20,6 +20,10 @@ _require_test_program dio-append-buf-fault
 _fixed_by_fs_commit btrfs 939b656bc8ab \
 	"btrfs: fix corruption after buffer fault in during direct IO append write"
 
+# Remove the existing file, so a new inode can be created, and will be
+# affected by changed mount options.
+rm -rf $TEST_DIR/dio-append-buf-fault
+
 # On error the test program writes messages to stderr, causing a golden output
 # mismatch and making the test fail.
 $here/src/dio-append-buf-fault $TEST_DIR/dio-append-buf-fault
-- 
2.51.2