f2fs: add feature facility in superblock

This patch introduces a feature in superblock, which will indicate any new
features for f2fs.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index cd9748a..e1dd986 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -70,6 +70,13 @@
 	unsigned int	opt;
 };
 
+#define F2FS_HAS_FEATURE(sb, mask)					\
+	((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
+#define F2FS_SET_FEATURE(sb, mask)					\
+	F2FS_SB(sb)->raw_super->feature |= cpu_to_le32(mask)
+#define F2FS_CLEAR_FEATURE(sb, mask)					\
+	F2FS_SB(sb)->raw_super->feature &= ~cpu_to_le32(mask)
+
 #define CRCPOLY_LE 0xedb88320
 
 static inline __u32 f2fs_crc32(void *buf, size_t len)