ext4: snapshot rocompat - enable rw mount

Enable readwrite mount of filesystem with has_snapshot feature only
if ext4 was compiled with snapshot support.


Signed-off-by: Amir Goldstein <amir73il@users.sf.net>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>

fs/ext4/ext4.h

@@ -1483,6 +1483,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 					 EXT4_FEATURE_INCOMPAT_FLEX_BG)
 #define EXT4_FEATURE_RO_COMPAT_SUPP	(EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
 					 EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+					 EXT4_FEATURE_RO_COMPAT_HAS_SNAPSHOT| \
 					 EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
 					 EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
 					 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \

fs/ext4/super.c

@@ -2693,6 +2693,16 @@ static int ext4_feature_set_ok(struct super_block *sb, int readonly)
 				"must run fsck -xy to make it writable.");
 			return 0;
 		}
+	} else if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
+			EXT4_FEATURE_RO_COMPAT_HAS_SNAPSHOT)) {
+		/*
+		 * We get here when CONFIG_EXT4_FS_SNAPSHOT is not defined
+		 * so EXT4_SNAPSHOTS(sb) is defined to (0)
+		 */
+		ext4_msg(sb, KERN_ERR,
+			"Filesystem with has_snapshot feature cannot be "
+			"mounted RDWR without CONFIG_EXT4_FS_SNAPSHOT");
+		return 0;
 	}
 	return 1;
 }