overlay: correctly handle dependency tracking

src/lxc/storage/overlay.c

@@ -186,10 +186,11 @@ int ovl_clonepaths(struct lxc_storage *orig, struct lxc_storage *new, const char
 		}
 	} else if (!strcmp(orig->type, "overlayfs") ||
 		   !strcmp(orig->type, "overlay")) {
-		char *osrc, *odelta, *nsrc, *ndelta, *work;
-		char *lastslash;
+		char *clean_old_path, *clean_new_path;
+		char *lastslash, *ndelta, *nsrc, *odelta, *osrc, *s1, *s2, *s3,
+		    *work;
 		int ret, lastslashidx;
-		size_t len;
+		size_t len, name_len;
 
 		osrc = strdup(orig->src);
 		if (!osrc) {
@@ -298,7 +299,93 @@ int ovl_clonepaths(struct lxc_storage *orig, struct lxc_storage *new, const char
 			return -1;
 		}
 
-		return ovl_do_rsync(orig, new, conf);
+		ret = ovl_do_rsync(orig, new, conf);
+		if (ret < 0)
+			return -1;
+
+		/* When we create an overlay snapshot of an overlay container in
+		 * the snapshot directory under "<lxcpath>/<name>/snaps/" we
+		 * don't need to record a dependency. If we would restore would
+		 * also fail.
+		 */
+		clean_old_path = lxc_deslashify(oldpath);
+		if (!clean_old_path)
+			return -1;
+
+		clean_new_path = lxc_deslashify(lxcpath);
+		if (!clean_new_path) {
+			free(clean_old_path);
+			return -1;
+		}
+
+		s1 = strrchr(clean_old_path, '/');
+		if (!s1) {
+			ERROR("Failed to detect \"/\" in string \"%s\"", s1);
+			free(clean_old_path);
+			free(clean_new_path);
+			return -1;
+		}
+
+		s2 = strrchr(clean_new_path, '/');
+		if (!s2) {
+			ERROR("Failed to detect \"/\" in string \"%s\"", s2);
+			free(clean_old_path);
+			free(clean_new_path);
+			return -1;
+		}
+
+		if (!strncmp(s1, "/snaps", sizeof("/snaps") - 1)) {
+			s1 = clean_new_path;
+			s2 = clean_old_path;
+			s3 = (char *)cname;
+			name_len = strlen(cname);
+			len = strlen(clean_new_path);
+		} else if (!strncmp(s2, "/snaps", sizeof("/snaps") - 1)) {
+			s1 = clean_old_path;
+			s2 = clean_new_path;
+			s3 = (char *)oldname;
+			name_len = strlen(oldname);
+			len = strlen(clean_old_path);
+		} else {
+			free(clean_old_path);
+			free(clean_new_path);
+			return 0;
+		}
+
+		if (!strncmp(s1, s2, len)) {
+			char *tmp;
+
+			tmp = (char *)(s2 + len + 1);
+			if (*tmp == '\0') {
+				free(clean_old_path);
+				free(clean_new_path);
+				return 0;
+			}
+
+			name_len = strlen(s3);
+			if (strncmp(s3, tmp, name_len)) {
+				free(clean_old_path);
+				free(clean_new_path);
+				return 0;
+			}
+
+			tmp += name_len + 1;
+			if (*tmp == '\0') {
+				free(clean_old_path);
+				free(clean_new_path);
+				return 0;
+			}
+
+			if (!strncmp(tmp, "snaps", sizeof("snaps") - 1)) {
+				free(clean_old_path);
+				free(clean_new_path);
+				return LXC_CLONE_SNAPSHOT;
+			}
+		}
+
+		free(clean_old_path);
+		free(clean_new_path);
+		return 0;
 	} else {
 		ERROR("overlay clone of %s container is not yet supported",
 		      orig->type);

src/lxc/storage/storage.c

@@ -386,7 +386,7 @@ struct lxc_storage *storage_copy(struct lxc_container *c, const char *cname,
 		snap = false;
 
 	/* If newtype is NULL and snapshot is set, then use overlay. */
-	if (!bdevtype && !keepbdevtype && snap && strcmp(orig->type, "dir") == 0)
+	if (!bdevtype && !keepbdevtype && snap && !strcmp(orig->type, "dir"))
 		bdevtype = "overlay";
 
 	if (am_unpriv() && !unpriv_snap_allowed(orig, bdevtype, snap, maybe_snap)) {
@@ -396,21 +396,24 @@ struct lxc_storage *storage_copy(struct lxc_container *c, const char *cname,
 	}
 
 	*needs_rdep = false;
-	if (bdevtype && !strcmp(orig->type, "dir") &&
-	    (strcmp(bdevtype, "aufs") == 0 ||
-	     strcmp(bdevtype, "overlayfs") == 0 ||
-	     strcmp(bdevtype, "overlay") == 0)) {
+	if (bdevtype) {
+		if (snap && !strcmp(orig->type, "lvm") &&
+		    !lvm_is_thin_volume(orig->src))
 			*needs_rdep = true;
-	} else if (snap && !strcmp(orig->type, "lvm") &&
-		   !lvm_is_thin_volume(orig->src)) {
+		else if (!strcmp(bdevtype, "overlay") ||
+			 !strcmp(bdevtype, "overlayfs"))
 			*needs_rdep = true;
-	}
-
-	if (strcmp(oldpath, lxcpath) && !bdevtype && !snap)
+	} else {
+		if (!snap && strcmp(oldpath, lxcpath))
 			bdevtype = "dir";
-	else if (!bdevtype)
+		else
 			bdevtype = orig->type;
 
+		if (!strcmp(bdevtype, "overlay") ||
+		    !strcmp(bdevtype, "overlayfs"))
+			*needs_rdep = true;
+	}
+
 	/* get new bdev type */
 	new = storage_get(bdevtype);
 	if (!new) {
@@ -428,6 +431,15 @@ struct lxc_storage *storage_copy(struct lxc_container *c, const char *cname,
 		goto on_error_put_new;
 	}
 
+	/* When we create an overlay snapshot of an overlay container in the
+	 * snapshot directory under "<lxcpath>/<name>/snaps/" we don't need to
+	 * record a dependency. If we would restore would also fail.
+	 */
+	if ((!strcmp(new->type, "overlay") ||
+	     !strcmp(new->type, "overlayfs")) &&
+	    ret == LXC_CLONE_SNAPSHOT)
+		*needs_rdep = false;
+
 	/* btrfs */
 	if (!strcmp(orig->type, "btrfs") && !strcmp(new->type, "btrfs")) {
 		bool bret = false;