bcachefs: Validate bset version field against sb version fields

The superblock version fields need to be accurate to know whether a
filesystem is supported, thus we should be verifying them.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -592,6 +592,7 @@ struct bch_fs {
 		__uuid_t	user_uuid;
 
 		u16		version;
+		u16		version_min;
 		u16		encoded_extent_max;
 
 		u8		nr_devices;

fs/bcachefs/btree_io.c

@@ -560,6 +560,26 @@ static int validate_bset(struct bch_fs *c, struct bch_dev *ca,
 		     BTREE_ERR_FATAL, c, ca, b, i,
 		     "unsupported bset version");
 
+	if (btree_err_on(version < c->sb.version_min,
+			 BTREE_ERR_FIXABLE, c, NULL, b, i,
+			 "bset version %u older than superblock version_min %u",
+			 version, c->sb.version_min)) {
+		mutex_lock(&c->sb_lock);
+		c->disk_sb.sb->version_min = cpu_to_le16(version);
+		bch2_write_super(c);
+		mutex_unlock(&c->sb_lock);
+	}
+
+	if (btree_err_on(version > c->sb.version,
+			 BTREE_ERR_FIXABLE, c, NULL, b, i,
+			 "bset version %u newer than superblock version %u",
+			 version, c->sb.version)) {
+		mutex_lock(&c->sb_lock);
+		c->disk_sb.sb->version = cpu_to_le16(version);
+		bch2_write_super(c);
+		mutex_unlock(&c->sb_lock);
+	}
+
 	if (btree_err_on(b->written + sectors > c->opts.btree_node_size,
 			 BTREE_ERR_FIXABLE, c, ca, b, i,
 			 "bset past end of btree node")) {

fs/bcachefs/super-io.c

@@ -369,6 +369,7 @@ static void bch2_sb_update(struct bch_fs *c)
 	c->sb.uuid		= src->uuid;
 	c->sb.user_uuid		= src->user_uuid;
 	c->sb.version		= le16_to_cpu(src->version);
+	c->sb.version_min	= le16_to_cpu(src->version_min);
 	c->sb.nr_devices	= src->nr_devices;
 	c->sb.clean		= BCH_SB_CLEAN(src);
 	c->sb.encryption_type	= BCH_SB_ENCRYPTION_TYPE(src);