f2fs: introduce dot and dotdot name check

This patch adds an inline function to check dot and dotdot names.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1454,6 +1454,17 @@ static inline void f2fs_stop_checkpoint(struct f2fs_sb_info *sbi)
 	sbi->sb->s_flags |= MS_RDONLY;
 }
 
+static inline bool is_dot_dotdot(const struct qstr *str)
+{
+	if (str->len == 1 && str->name[0] == '.')
+		return true;
+
+	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
+		return true;
+
+	return false;
+}
+
 #define get_inode_mode(i) \
 	((is_inode_flag_set(F2FS_I(i), FI_ACL_MODE)) ? \
 	 (F2FS_I(i)->i_acl_mode) : ((i)->i_mode))

fs/f2fs/hash.c

@@ -79,8 +79,7 @@ f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info)
 	const unsigned char *name = name_info->name;
 	size_t len = name_info->len;
 
-	if ((len <= 2) && (name[0] == '.') &&
-		(name[1] == '.' || name[1] == '\0'))
+	if (is_dot_dotdot(name_info))
 		return 0;
 
 	/* Initialize the default seed for the hash checksum functions */