storage: make storage_dir() smart

src/lxc/lxccontainer.c

@@ -3802,7 +3802,7 @@ static int do_lxcapi_snapshot(struct lxc_container *c, const char *commentfile)
 	 */
 	flags = LXC_CLONE_SNAPSHOT | LXC_CLONE_KEEPMACADDR | LXC_CLONE_KEEPNAME |
 		LXC_CLONE_KEEPBDEVTYPE | LXC_CLONE_MAYBE_SNAPSHOT;
-	if (storage_is_dir(c->lxc_conf, c->lxc_conf->rootfs.path)) {
+	if (storage_is_dir(c->lxc_conf)) {
 		ERROR("Snapshot of directory-backed container requested.");
 		ERROR("Making a copy-clone.  If you do want snapshots, then");
 		ERROR("please create an aufs or overlay clone first, snapshot that");

src/lxc/storage/storage.c

@@ -650,12 +650,16 @@ struct lxc_storage *storage_init(struct lxc_conf *conf, const char *src,
 	return bdev;
 }
 
-bool storage_is_dir(struct lxc_conf *conf, const char *path)
+bool storage_is_dir(struct lxc_conf *conf)
 {
 	struct lxc_storage *orig;
+	char *type = conf->rootfs.bdev_type;
 	bool bret = false;
 
-	orig = storage_init(conf, path, NULL, NULL);
+	if (type)
+		return (strcmp(type, "dir") == 0);
+
+	orig = storage_init(conf, conf->lxc_rootfs.path, NULL, NULL);
 	if (!orig)
 		return bret;
 

src/lxc/storage/storage.h

@@ -109,7 +109,19 @@ struct lxc_storage {
 	int flags;
 };
 
-extern bool storage_is_dir(struct lxc_conf *conf, const char *path);
+/**
+ * storage_is_dir : Check whether the roots is a directory. This function will
+ *                  trust the config file. If the config file key
+ *                  lxc.rootfs.path is set to <storage type>:<container path>
+ *                  the confile parser will have split this into <storage type>
+ *                  and <container path> and set the <bdev_type> member in the
+ *                  lxc_rootfs struct to <storage type> and the <path> member
+ *                  will be set to a clean <container path> without the <storage
+ *                  type> prefix. This is the new, clean way of handling storage
+ *                  type specifications.  If the <storage type> prefix is not
+ *                  detected liblxc will try to detect the storage type.
+ */
+extern bool storage_is_dir(struct lxc_conf *conf);
 extern bool storage_can_backup(struct lxc_conf *conf);
 
 /* Instantiate a lxc_storage object. The src is used to determine which blockdev