overlay: correctly restore from snapshot

src/lxc/storage/btrfs.c

@@ -438,8 +438,8 @@ bool btrfs_create_clone(struct lxc_conf *conf, struct lxc_storage *orig,
 	data.orig = orig;
 	data.new = new;
 	if (am_unpriv()) {
-		ret = userns_exec_1(conf, lxc_rsync_exec_wrapper, &data,
-				    "lxc_rsync_exec_wrapper");
+		ret = userns_exec_1(conf, lxc_storage_rsync_exec_wrapper, &data,
+				    "lxc_storage_rsync_exec_wrapper");
 		if (ret < 0) {
 			ERROR("Failed to rsync from \"%s\" into \"%s\"",
 			      orig->dest, new->dest);
@@ -450,7 +450,7 @@ bool btrfs_create_clone(struct lxc_conf *conf, struct lxc_storage *orig,
 	}
 
 	ret = run_command(cmd_output, sizeof(cmd_output),
-			lxc_rsync_exec_wrapper, (void *)&data);
+			lxc_storage_rsync_exec_wrapper, (void *)&data);
 	if (ret < 0) {
 		ERROR("Failed to rsync from \"%s\" into \"%s\": %s", orig->dest,
 		      new->dest, cmd_output);

src/lxc/storage/lvm.c

@@ -507,7 +507,7 @@ bool lvm_create_clone(struct lxc_conf *conf, struct lxc_storage *orig,
 	data.orig = orig;
 	data.new = new;
 	ret = run_command(cmd_output, sizeof(cmd_output),
-			  lxc_rsync_exec_wrapper, (void *)&data);
+			  lxc_storage_rsync_exec_wrapper, (void *)&data);
 	if (ret < 0) {
 		ERROR("Failed to rsync from \"%s\" to \"%s\"", orig->dest,
 		      new->dest);

src/lxc/storage/overlay.c

@@ -43,7 +43,7 @@ static char *ovl_name;
 static char *ovl_version[] = {"overlay", "overlayfs"};
 
 static char *ovl_detect_name(void);
-static int ovl_do_rsync(struct lxc_storage *orig, struct lxc_storage *new,
+static int ovl_do_rsync(const char *src, const char *dest,
 			struct lxc_conf *conf);
 static int ovl_remount_on_enodev(const char *lower, const char *target,
 				 const char *name, unsigned long mountflags,
@@ -292,14 +292,16 @@ int ovl_clonepaths(struct lxc_storage *orig, struct lxc_storage *new, const char
 			return -ENOMEM;
 		}
 		ret = snprintf(new->src, len, "overlay:%s:%s", nsrc, ndelta);
-		free(osrc);
-		free(ndelta);
 		if (ret < 0 || (size_t)ret >= len) {
 			ERROR("Failed to create string");
+			free(osrc);
+			free(ndelta);
 			return -1;
 		}
 
-		ret = ovl_do_rsync(orig, new, conf);
+		ret = ovl_do_rsync(odelta, ndelta, conf);
+		free(osrc);
+		free(ndelta);
 		if (ret < 0)
 			return -1;
 
@@ -462,6 +464,12 @@ int ovl_destroy(struct lxc_storage *orig)
 	if (!ovl && strncmp(upper, "overlayfs:", 10))
 		return -22;
 
+	/* For an overlay container the rootfs is considered immutable
+	 * and cannot be removed when restoring from a snapshot.
+	 */
+	if (orig->flags & LXC_STORAGE_INTERNAL_OVERLAY_RESTORE)
+		return 0;
+
 	if (ovl)
 		upper += 8;
 	else
@@ -953,28 +961,25 @@ static char *ovl_detect_name(void)
 	return v;
 }
 
-static int ovl_do_rsync(struct lxc_storage *orig, struct lxc_storage *new,
+static int ovl_do_rsync(const char *src, const char *dest,
 			struct lxc_conf *conf)
 {
 	int ret = -1;
-	struct rsync_data rdata = {0, 0};
+	struct rsync_data_char rdata = {0};
 	char cmd_output[MAXPATHLEN] = {0};
 
-	rdata.orig = orig;
-	rdata.new = new;
-	if (am_unpriv()) {
+	rdata.src = (char *)src;
+	rdata.dest = (char *)dest;
+	if (am_unpriv())
 		ret = userns_exec_1(conf, lxc_rsync_exec_wrapper, &rdata,
 				    "lxc_rsync_exec_wrapper");
-		if (ret < 0)
-			ERROR("Failed to rsync from \"%s\" into \"%s\"",
-			      orig->dest, new->dest);
-	} else {
+	else
 		ret = run_command(cmd_output, sizeof(cmd_output),
 				  lxc_rsync_exec_wrapper, (void *)&rdata);
 	if (ret < 0)
-			ERROR("Failed to rsync from \"%s\" into \"%s\": %s",
-			      orig->dest, new->dest, cmd_output);
-	}
+		ERROR("Failed to rsync from \"%s\" into \"%s\"%s%s", src, dest,
+		      cmd_output[0] != '\0' ? ": " : "",
+		      cmd_output[0] != '\0' ? cmd_output : "");
 
 	return ret;
 }

src/lxc/storage/rsync.c

@@ -39,12 +39,28 @@
 
 lxc_log_define(rsync, lxc);
 
-int lxc_rsync_exec_wrapper(void *data)
+int lxc_storage_rsync_exec_wrapper(void *data)
 {
 	struct rsync_data *arg = data;
 	return lxc_rsync(arg);
 }
 
+int lxc_rsync_exec_wrapper(void *data)
+{
+	int ret;
+	struct rsync_data_char *args = data;
+
+	ret = lxc_switch_uid_gid(0, 0);
+	if (ret < 0)
+		return -1;
+
+	ret = lxc_setgroups(0, NULL);
+	if (ret < 0)
+		return -1;
+
+	return lxc_rsync_exec(args->src, args->dest);
+}
+
 int lxc_rsync_exec(const char *src, const char *dest)
 {
 	int ret;
@@ -70,8 +86,8 @@ int lxc_rsync_exec(const char *src, const char *dest)
 int lxc_rsync(struct rsync_data *data)
 {
 	int ret;
-	struct lxc_storage *orig = data->orig, *new = data->new;
 	char *dest, *src;
+	struct lxc_storage *orig = data->orig, *new = data->new;
 
 	ret = unshare(CLONE_NEWNS);
 	if (ret < 0) {
@@ -101,6 +117,7 @@ int lxc_rsync(struct rsync_data *data)
 	ret = lxc_switch_uid_gid(0, 0);
 	if (ret < 0)
 		return -1;
+
 	ret = lxc_setgroups(0, NULL);
 	if (ret < 0)
 		return -1;

src/lxc/storage/rsync.h

@@ -39,6 +39,7 @@ struct rsync_data_char {
 
 /* new helpers */
 extern int lxc_rsync_exec_wrapper(void *data);
+extern int lxc_storage_rsync_exec_wrapper(void *data);
 extern int lxc_rsync_exec(const char *src, const char *dest);
 extern int lxc_rsync(struct rsync_data *data);
 

src/lxc/storage/storage.c

@@ -502,11 +502,11 @@ struct lxc_storage *storage_copy(struct lxc_container *c, const char *cname,
 	data.orig = orig;
 	data.new = new;
 	if (am_unpriv())
-		ret = userns_exec_1(c->lxc_conf, lxc_rsync_exec_wrapper, &data,
-				    "lxc_rsync_exec_wrapper");
+		ret = userns_exec_1(c->lxc_conf, lxc_storage_rsync_exec_wrapper,
+				    &data, "lxc_storage_rsync_exec_wrapper");
 	else
 		ret = run_command(cmd_output, sizeof(cmd_output),
-				  lxc_rsync_exec_wrapper, (void *)&data);
+				  lxc_storage_rsync_exec_wrapper, (void *)&data);
 	if (ret < 0) {
 		ERROR("Failed to rsync from \"%s\" into \"%s\"%s%s", orig->dest,
 		      new->dest,
@@ -598,6 +598,8 @@ struct lxc_storage *storage_init(struct lxc_conf *conf, const char *src,
 	struct lxc_storage *bdev;
 	const struct lxc_storage_type *q;
 
+	BUILD_BUG_ON(LXC_STORAGE_INTERNAL_OVERLAY_RESTORE <= LXC_CLONE_MAXFLAGS);
+
 	if (!src)
 		src = conf->rootfs.path;
 

src/lxc/storage/storage.h

@@ -57,6 +57,8 @@
 #define DEFAULT_FS_SIZE 1073741824
 #define DEFAULT_FSTYPE "ext3"
 
+#define LXC_STORAGE_INTERNAL_OVERLAY_RESTORE  (1 << 6)
+
 struct lxc_storage;
 
 struct lxc_storage_ops {
@@ -97,6 +99,7 @@ struct lxc_storage {
 	int lofd;
 	/* index for the connected nbd device. */
 	int nbd_idx;
+	int flags;
 };
 
 extern bool storage_is_dir(struct lxc_conf *conf, const char *path);

src/lxc/storage/zfs.c

@@ -325,7 +325,7 @@ bool zfs_copy(struct lxc_conf *conf, struct lxc_storage *orig,
 	data.orig = orig;
 	data.new = new;
 	ret = run_command(cmd_output, sizeof(cmd_output),
-			  lxc_rsync_exec_wrapper, (void *)&data);
+			  lxc_storage_rsync_exec_wrapper, (void *)&data);
 	if (ret < 0) {
 		ERROR("Failed to rsync from \"%s\" into \"%s\": %s", orig->dest,
 		      new->dest, cmd_output);