fsck.f2fs: disable linear lookup by default

As we know, Android is the only user of casefold feature, in casefolded
directory, creating a filename w/ character has ignorable code points in
buggy kernel v6.12 is a very rare case, we don't get any report that user
can not access file w/ character has ignorable code points till now.

Let's disable linear lookup in fsck for Android by default, once there is
any related bug report of unicode code points, we can enable it again.

mkfs.f2fs -f -O casefold -C utf8 /dev/vdb
dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
s_encoding_flags                        [0x       0 : 0]
fsck.f2fs /dev/vdb -g android
dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
s_encoding_flags                        [0x       2 : 2]

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fsck/main.c

@@ -91,7 +91,7 @@ void fsck_usage()
 	MSG(0, "  --no-kernel-check skips detecting kernel change\n");
 	MSG(0, "  --kernel-check checks kernel change\n");
 	MSG(0, "  --debug-cache to debug cache when -c is used\n");
-	MSG(0, "  --nolinear-lookup=X X=1: disable linear lookup, X=0: enable linear lookup\n");
+	MSG(0, "  --nolinear-lookup=X X=1: disable linear lookup, X=0: enable linear lookup. For android case, it will disable linear lookup by default\n");
 	MSG(0, "  --fault_injection=%%d to enable fault injection with specified injection rate\n");
 	MSG(0, "  --fault_type=%%d to configure enabled fault injection type\n");
 	exit(1);
@@ -224,6 +224,9 @@ static void add_default_options(void)
 		if (c.func == FSCK) {
 			/* -a */
 			c.auto_fix = 1;
+
+			/* disable linear lookup by default */
+			c.nolinear_lookup = LINEAR_LOOKUP_DISABLE;
 		} else if (c.func == RESIZE) {
 			c.force = 1;
 		}

man/fsck.f2fs.8

@@ -68,7 +68,7 @@ Specify the level of debugging options.
 The default number is 0, which shows basic debugging messages.
 .TP
 .BI \--nolinear-lookup
-Tune linear lookup fallback, must specify an argument, 0: enable linear lookup, 1: disable linear lookup.
+Tune linear lookup fallback, must specify an argument, 0: enable linear lookup, 1: disable linear lookup. For android case, it will disable linear lookup by default.
 .TP
 .BI \-\-fault_injection=%d " enable fault injection"
 Enable fault injection in all supported types with specified injection rate.