c/r: pass --cgroup-roots on checkpoint

CRIU has added support for passing --cgroup-root on dump, which we should
use (see the criu commit 07d259f365f224b32914de26ea0fd59fc6db0001 for
details). Note that we don't have to do any version checking or anything,
because CRIU just ignored --cgroup-root on checkpoint before, so passing it
is safe, and will result in correct behavior when a sufficient version of
CRIU is present.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>

src/lxc/criu.c

@@ -69,7 +69,7 @@ struct criu_opts {
 	char tty_id[32]; /* the criu tty id for /dev/console, i.e. "tty[${rdev}:${dev}]" */
 
 	/* restore: the file to write the init process' pid into */
-	const char *cgroup_path;
+	struct lxc_handler *handler;
 	int console_fd;
 	/* The path that is bind mounted from /dev/console, if any. We don't
 	 * want to use `--ext-mount-map auto`'s result here because the pts
@@ -175,10 +175,10 @@ static void exec_criu(struct criu_opts *opts)
 			static_args += 2;
 	} else if (strcmp(opts->action, "restore") == 0) {
 		/* --root $(lxc_mount_point) --restore-detached
-		 * --restore-sibling --cgroup-root $foo
+		 * --restore-sibling
 		 * --lsm-profile apparmor:whatever
 		 */
-		static_args += 8;
+		static_args += 6;
 
 		tty_info[0] = 0;
 		if (load_tty_major_minor(opts->user->directory, tty_info, sizeof(tty_info)))
@@ -191,6 +191,8 @@ static void exec_criu(struct criu_opts *opts)
 		return;
 	}
 
+	static_args += 2 * cgroup_num_hierarchies();
+
 	if (opts->user->verbose)
 		static_args++;
 
@@ -244,6 +246,66 @@ static void exec_criu(struct criu_opts *opts)
 	DECLARE_ARG("-o");
 	DECLARE_ARG(log);
 
+	for (i = 0; i < cgroup_num_hierarchies(); i++) {
+		char **controllers = NULL, *fullname;
+		char *path;
+
+		if (!cgroup_get_hierarchies(i, &controllers)) {
+			ERROR("failed to get hierarchy %d", i);
+			goto err;
+		}
+
+		/* if we are in a dump, we have to ask the monitor process what
+		 * the right cgroup is. if this is a restore, we can just use
+		 * the handler the restore task created.
+		 */
+		if (!strcmp(opts->action, "dump") || !strcmp(opts->action, "pre-dump")) {
+			path = lxc_cmd_get_cgroup_path(opts->c->name, opts->c->config_path, controllers[0]);
+			if (!path) {
+				ERROR("failed to get cgroup path for %s", controllers[0]);
+				goto err;
+			}
+		} else {
+			const char *p;
+
+			p = cgroup_get_cgroup(opts->handler, controllers[0]);
+			if (!p) {
+				ERROR("failed to get cgroup path for %s", controllers[0]);
+				goto err;
+			}
+
+			path = strdup(p);
+			if (!path) {
+				ERROR("strdup failed");
+				goto err;
+			}
+		}
+
+		if (!lxc_deslashify(path)) {
+			ERROR("failed to deslashify %s", path);
+			free(path);
+			goto err;
+		}
+
+		fullname = lxc_string_join(",", (const char **) controllers, false);
+		if (!fullname) {
+			ERROR("failed to join controllers");
+			free(path);
+			goto err;
+		}
+
+		ret = sprintf(buf, "%s:%s", fullname, path);
+		free(path);
+		free(fullname);
+		if (ret < 0 || ret >= sizeof(buf)) {
+			ERROR("sprintf of cgroup root arg failed");
+			goto err;
+		}
+
+		DECLARE_ARG("--cgroup-root");
+		DECLARE_ARG(buf);
+	}
+
 	if (opts->user->verbose)
 		DECLARE_ARG("-vvvvvv");
 
@@ -329,8 +391,6 @@ static void exec_criu(struct criu_opts *opts)
 		DECLARE_ARG(opts->c->lxc_conf->rootfs.mount);
 		DECLARE_ARG("--restore-detached");
 		DECLARE_ARG("--restore-sibling");
-		DECLARE_ARG("--cgroup-root");
-		DECLARE_ARG(opts->cgroup_path);
 
 		if (tty_info[0]) {
 			if (opts->console_fd < 0) {
@@ -682,9 +742,9 @@ static void do_restore(struct lxc_container *c, int status_pipe, struct migrate_
 		os.action = "restore";
 		os.user = opts;
 		os.c = c;
-		os.cgroup_path = cgroup_canonical_path(handler);
 		os.console_fd = c->lxc_conf->console.slave;
 		os.criu_version = criu_version;
+		os.handler = handler;
 
 		if (os.console_fd >= 0) {
 			/* Twiddle the FD_CLOEXEC bit. We want to pass this FD to criu
@@ -891,6 +951,13 @@ static bool do_dump(struct lxc_container *c, char *mode, struct migrate_opts *op
 
 	if (pid == 0) {
 		struct criu_opts os;
+		struct lxc_handler h;
+
+		h.name = c->name;
+		if (!cgroup_init(&h)) {
+			ERROR("failed to cgroup_init()");
+			exit(1);
+		}
 
 		os.action = mode;
 		os.user = opts;