f2fs/012: test red heart lookup

As Han Qi reported in bugzilla [1], commit 5c26d2f1d3f5 ("unicode: Don't
special case ignorable code points") changes logic to handle ignorable
code points, when we handle filename which has special unicode charactor
like red heart ❤️, utf8_casefold() may return different length than in the
past, result in that f2fs cacluates hash code incorreclty, eventually,
filename w/ special unicode charactor will not be found w/ the wrong hash
code.

f2fs has introduced a linear lookup fallback w/ commit 91b587ba79e1
("f2fs: Introduce linear search for dentries"), once hash-based lookup
fails, it tries linear lookup as a fallback.

This patch can help to check whether linear lookup fallback works well
or not.

Firstly, we use below testcase to check how hash code changes:

mkfs.f2fs -f -O casefold -C utf8 /dev/vda
mount /dev/vda /mnt/f2fs
mkdir /mnt/f2fs/dir/
f2fs_io setflags casefold /mnt/f2fs/dir
touch /mnt/f2fs/dir/$'\u2764\ufe0f'
umount /mnt/f2fs
dump.f2fs -i 4 -d 3 /dev/vda
dump.f2fs -b $blkaddr_of_dir -d 3 /dev/vda

w/o ("unicode: Don't special case ignorable code points")
[dump_dirent: 991] bitmap pos[0x2] name[❤️] len[0x6] hash[0x19dd7132] ino[0x5] type[0x1]
[dump_dirent: 998] name(hex)[0xe2 0x9d 0xa4 0xef 0xb8 0x8f 0x0]

w/ ("unicode: Don't special case ignorable code points")
[dump_dirent: 991] bitmap pos[0x2] name[❤️] len[0x6] hash[0x9a2ea068] ino[0x5] type[0x1]
[dump_dirent: 998] name(hex)[0xe2 0x9d 0xa4 0xef 0xb8 0x8f 0x0]

Correct hash code:	0x19dd7132
Wrong hash code:	0x9a2ea068

So, we can test as below:

1. create file w/ red heart as its filename
2. inject wrong hash code to the file
3. disable linear lookup, expect lookup failure
4. enable linear lookup, expect lookup succeed

[1] https://bugzilla.kernel.org/show_bug.cgi?id=219586

Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Daniel Lee <chullee@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>

diff --git a/tests/f2fs/012 b/tests/f2fs/012
new file mode 100755 (executable)
index 0000000..b3df9a8
--- /dev/null
+++ b/tests/f2fs/012
@@ -0,0 +1,70 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2025 Chao Yu.  All Rights Reserved.
+#
+# FS QA Test No. f2fs/012
+#
+# This testcase checks whether linear lookup fallback works well
+# or not as below:
+# 1.create file w/ red heart as its filename
+# 2.inject wrong hash code to the file
+# 3.disable linear lookup, expect lookup failure
+# 4.enable linear lookup, expect lookup succeed
+#
+. ./common/preamble
+_begin_fstest auto quick casefold
+
+_fixed_by_kernel_commit 91b587ba79e1 \
+       "f2fs: Introduce linear search for dentries"
+
+export LC_ALL=C.UTF-8
+_require_scratch_nocheck
+_require_command "$F2FS_IO_PROG" f2fs_io
+_require_command "$F2FS_INJECT_PROG" inject.f2fs
+
+check_lookup()
+{
+       local nolinear_lookup=$1
+       local dir=$SCRATCH_MNT/dir
+       # red heart charactor in unicode format
+       local redheart=$dir/$'\u2764\ufe0f'
+
+       _scratch_mkfs -O casefold -C utf8 >> $seqres.full
+       _scratch_mount
+
+       mkdir $dir
+       $F2FS_IO_PROG setflags casefold $dir >> $seqres.full
+       touch $redheart
+       ino=`stat -c '%i' $redheart`
+       _scratch_unmount
+
+       # should tune nolinear_lookup feature before fault injection
+       $F2FS_FSCK_PROG --nolinear-lookup=$nolinear_lookup $SCRATCH_DEV >> $seqres.full
+
+       # check whether linear_lookup is changed as expected
+       if [ $nolinear_lookup == "1" ]; then
+               $F2FS_FSCK_PROG $SCRATCH_DEV | grep -q "linear_lookup \[disable\]" ||   \
+                                       _fail "linear_lookup is not disabled"
+       else
+               $F2FS_FSCK_PROG $SCRATCH_DEV | grep -q "linear_lookup \[enable\]" ||    \
+                                       _fail "linear_lookup is not enabled"
+       fi
+
+       $F2FS_INJECT_PROG --dent --mb d_hash --nid $ino --val 0x9a2ea068 $SCRATCH_DEV >> $seqres.full
+
+       _scratch_mount
+       if [ $nolinear_lookup == "1" ]; then
+               [ -f $redheart ] && _fail "red heart file should not exist"
+       else
+               [ -f $redheart ] || _fail "red heart file should exist"
+       fi
+       _scratch_unmount
+}
+
+check_lookup 1
+check_lookup 0
+
+echo "Silence is golden"
+
+status=0
+exit

diff --git a/tests/f2fs/012.out b/tests/f2fs/012.out
new file mode 100644 (file)
index 0000000..3afeca2
--- /dev/null
+++ b/tests/f2fs/012.out
@@ -0,0 +1,2 @@
+QA output created by 012
+Silence is golden