Do not allow snapshots of LVM backed containers

src/lxc/bdev.c

@@ -520,6 +520,7 @@ static const struct bdev_ops dir_ops = {
 	.destroy = &dir_destroy,
 	.create = &dir_create,
 	.can_snapshot = false,
+	.can_backup = true,
 };
 
 
@@ -784,6 +785,7 @@ static const struct bdev_ops zfs_ops = {
 	.destroy = &zfs_destroy,
 	.create = &zfs_create,
 	.can_snapshot = true,
+	.can_backup = true,
 };
 
 //
@@ -1179,6 +1181,7 @@ static const struct bdev_ops lvm_ops = {
 	.destroy = &lvm_destroy,
 	.create = &lvm_create,
 	.can_snapshot = true,
+	.can_backup = false,
 };
 
 /*
@@ -1858,6 +1861,7 @@ static const struct bdev_ops btrfs_ops = {
 	.destroy = &btrfs_destroy,
 	.create = &btrfs_create,
 	.can_snapshot = true,
+	.can_backup = true,
 };
 
 //
@@ -2129,6 +2133,7 @@ static const struct bdev_ops loop_ops = {
 	.destroy = &loop_destroy,
 	.create = &loop_create,
 	.can_snapshot = false,
+	.can_backup = true,
 };
 
 //
@@ -2426,6 +2431,7 @@ static const struct bdev_ops overlayfs_ops = {
 	.destroy = &overlayfs_destroy,
 	.create = &overlayfs_create,
 	.can_snapshot = true,
+	.can_backup = true,
 };
 
 //
@@ -2703,6 +2709,7 @@ static const struct bdev_ops aufs_ops = {
 	.destroy = &aufs_destroy,
 	.create = &aufs_create,
 	.can_snapshot = true,
+	.can_backup = true,
 };
 
 
@@ -2769,6 +2776,9 @@ struct bdev *bdev_init(const char *src, const char *dst, const char *mntopts)
 	struct bdev *bdev;
 	const struct bdev_type *q;
 
+	if (!src)
+		return NULL;
+
 	q = bdev_query(src);
 	if (!q)
 		return NULL;
@@ -2855,6 +2865,18 @@ bool bdev_is_dir(const char *path)
 	return ret;
 }
 
+bool bdev_can_backup(struct lxc_conf *conf)
+{
+	struct bdev *bdev = bdev_init(conf->rootfs.path, NULL, NULL);
+	bool ret;
+
+	if (!bdev)
+		return false;
+	ret = bdev->ops->can_backup;
+	bdev_put(bdev);
+	return ret;
+}
+
 /*
  * is an unprivileged user allowed to make this kind of snapshot
  */

src/lxc/bdev.h

@@ -48,6 +48,7 @@ struct bdev_ops {
 			const char *cname, const char *oldpath, const char *lxcpath,
 			int snap, uint64_t newsize, struct lxc_conf *conf);
 	bool can_snapshot;
+	bool can_backup;
 };
 
 /*
@@ -71,6 +72,7 @@ struct bdev {
 char *overlay_getlower(char *p);
 
 bool bdev_is_dir(const char *path);
+bool bdev_can_backup(struct lxc_conf *conf);
 
 /*
  * Instantiate a bdev object.  The src is used to determine which blockdev

src/lxc/lxccontainer.c

@@ -2865,6 +2865,12 @@ static int lxcapi_snapshot(struct lxc_container *c, const char *commentfile)
 	if (!c || !lxcapi_is_defined(c))
 		return -1;
 
+	if (!bdev_can_backup(c->lxc_conf)) {
+		ERROR("%s's backing store cannot be backed up.", c->name);
+		ERROR("Your container must use another backing store type.");
+		return -1;
+	}
+
 	// /var/lib/lxc -> /var/lib/lxcsnaps \0
 	ret = snprintf(snappath, MAXPATHLEN, "%ssnaps/%s", c->config_path, c->name);
 	if (ret < 0 || ret >= MAXPATHLEN)