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>

fs/f2fs/f2fs.h

@@ -70,6 +70,13 @@ struct f2fs_mount_info {
 	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)

include/linux/f2fs_fs.h

@@ -90,7 +90,8 @@ struct f2fs_super_block {
 	__le32 cp_payload;
 	__u8 version[VERSION_LEN];	/* the kernel version */
 	__u8 init_version[VERSION_LEN];	/* the initial kernel version */
-	__u8 reserved[892];		/* valid reserved region */
+	__le32 feature;			/* defined features */
+	__u8 reserved[888];		/* valid reserved region */
 } __packed;
 
 /*