lxcapi-snapshot: don't snapshot directory-backed containers

src/lxc/bdev.c

@@ -2116,6 +2116,19 @@ static int rsync_rootfs_wrapper(void *data)
 	struct rsync_data *arg = data;
 	return rsync_rootfs(arg);
 }
+
+bool bdev_is_dir(const char *path)
+{
+	struct bdev *orig = bdev_init(path, NULL, NULL);
+	bool ret = false;
+	if (!orig)
+		return ret;
+	if (strcmp(orig->type, "dir") == 0)
+		ret = true;
+	bdev_put(orig);
+	return ret;
+}
+
 /*
  * If we're not snaphotting, then bdev_copy becomes a simple case of mount
  * the original, mount the new, and rsync the contents.

src/lxc/bdev.h

@@ -86,6 +86,8 @@ struct bdev {
 
 char *overlayfs_getlower(char *p);
 
+bool bdev_is_dir(const char *path);
+
 /*
  * Instantiate a bdev object.  The src is used to determine which blockdev
  * type this should be.  The dst and data are optional, and will be used

src/lxc/lxccontainer.c

@@ -2827,6 +2827,13 @@ static int 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 (bdev_is_dir(c->lxc_conf->rootfs.path)) {
+		ERROR("Snapshot of directory-backed container requested.");
+		ERROR("Making a copy-clone.  If you do want snapshots, then");
+		ERROR("please create an overlayfs clone first, snapshot that");
+		ERROR("and keep the original container pristine.");
+		flags &= ~LXC_CLONE_SNAPSHOT | LXC_CLONE_MAYBE_SNAPSHOT;
+	}
 	c2 = c->clone(c, newname, snappath, flags, NULL, NULL, 0, NULL);
 	if (!c2) {
 		ERROR("clone of %s:%s failed", c->config_path, c->name);