f2fs: sysfs: export linear_lookup in features directory

cat /sys/fs/f2fs/features/linear_lookup
supported

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

Author: chaseyu

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -270,7 +270,7 @@ Description:	Shows all enabled kernel features.
 		inode_checksum, flexible_inline_xattr, quota_ino,
 		inode_crtime, lost_found, verity, sb_checksum,
 		casefold, readonly, compression, test_dummy_encryption_v2,
-		atomic_write, pin_file, encrypted_casefold.
+		atomic_write, pin_file, encrypted_casefold, linear_lookup.
 
 What:		/sys/fs/f2fs/<disk>/inject_rate
 Date:		May 2016

fs/f2fs/sysfs.c

@@ -1207,6 +1207,9 @@ F2FS_FEATURE_RO_ATTR(readonly);
 F2FS_FEATURE_RO_ATTR(compression);
 #endif
 F2FS_FEATURE_RO_ATTR(pin_file);
+#ifdef CONFIG_UNICODE
+F2FS_FEATURE_RO_ATTR(linear_lookup);
+#endif
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
@@ -1356,6 +1359,9 @@ static struct attribute *f2fs_feat_attrs[] = {
 	BASE_ATTR_LIST(compression),
 #endif
 	BASE_ATTR_LIST(pin_file),
+#ifdef CONFIG_UNICODE
+	BASE_ATTR_LIST(linear_lookup),
+#endif
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs_feat);