Revert "cgroups: Add ability to reuse existing cgroup yard directory"

Reasoning: some systems have /sys/fs/cgroup stuff mounted as read-only
and we have to either remount it rw or create our own set. The former
doesn't look sane as this rw remounting is also done by ststemd, so
let's return back to manual cgyard construction.

This reverts commit 860df95f.

Conflicts:
	cgroup.c
	include/cr_options.h
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Documentation/criu.txt

@@ -235,9 +235,6 @@ The '<mode>' may be one of below.
     Change the root cgroup the controller will be installed into. No controller
     means that root is the default for all controllers not specified.
 
-*--cgroup-yard* '<dir>'::
-   Use directory '<dir>' as cgroups yard instead of /sys/fs/cgroup.
-
 *--tcp-established*::
     Restore previously dumped established TCP connections. This implies that
     the network has been locked between *dump* and *restore* phases so other

cgroup.c

@@ -935,10 +935,14 @@ int prepare_task_cgroup(struct pstree_item *me)
 
 void fini_cgroup(void)
 {
-	if (cg_yard) {
-		close_service_fd(CGROUP_YARD);
-		cg_yard = NULL;
-	}
+	if (!cg_yard)
+		return;
+
+	close_service_fd(CGROUP_YARD);
+	umount2(cg_yard, MNT_DETACH);
+	rmdir(cg_yard);
+	xfree(cg_yard);
+	cg_yard = NULL;
 }
 
 static int restore_cgroup_prop(const CgroupPropEntry * cg_prop_entry_p,
@@ -1130,14 +1134,33 @@ static int prepare_cgroup_sfd(CgroupEntry *ce)
 	int off, i, ret;
 	char paux[PATH_MAX];
 
-	pr_info("Preparing cgroups yard (cgroups restore mode %#x)\n",
-		opts.manage_cgroups);
 	if (!opts.manage_cgroups)
 		return 0;
 
-	cg_yard = opts.cg_yard;
-	off = strlen(opts.cg_yard);
-	strcpy(paux, opts.cg_yard);
+	pr_info("Preparing cgroups yard (cgroups restore mode %#x)\n",
+		opts.manage_cgroups);
+
+	off = sprintf(paux, ".criu.cgyard.XXXXXX");
+	if (mkdtemp(paux) == NULL) {
+		pr_perror("Can't make temp cgyard dir");
+		return -1;
+	}
+
+	cg_yard = xstrdup(paux);
+	if (!cg_yard) {
+		rmdir(paux);
+		return -1;
+	}
+
+	if (mount("none", cg_yard, "tmpfs", 0, NULL)) {
+		pr_perror("Can't mount tmpfs in cgyard");
+		goto err;
+	}
+
+	if (mount("none", cg_yard, NULL, MS_PRIVATE, NULL)) {
+		pr_perror("Can't make cgyard private");
+		goto err;
+	}
 
 	pr_debug("Opening %s as cg yard\n", cg_yard);
 	i = open(cg_yard, O_DIRECTORY);

crtools.c

@@ -56,7 +56,6 @@ void init_opts(void)
 	INIT_LIST_HEAD(&opts.inherit_fds);
 	INIT_LIST_HEAD(&opts.new_cgroup_roots);
 
-	opts.cg_yard = "/sys/fs/cgroup";
 	opts.cpu_cap = CPU_CAP_DEFAULT;
 	opts.manage_cgroups = CG_MODE_DEFAULT;
 	opts.ps_socket = -1;
@@ -235,7 +234,6 @@ int main(int argc, char *argv[], char *envp[])
 		{ "enable-fs",			required_argument,	0, 1065 },
 		{ "enable-external-sharing", 	no_argument, 		0, 1066 },
 		{ "enable-external-masters", 	no_argument, 		0, 1067 },
-		{ "cgroup-yard",		required_argument,	0, 1068 },
 		{ },
 	};
 
@@ -464,9 +462,6 @@ int main(int argc, char *argv[], char *envp[])
 		case 1067:
 			opts.enable_external_masters = true;
 			break;
-		case 1068:
-			opts.cg_yard = optarg;
-			break;
 		case 'M':
 			{
 				char *aux;
@@ -708,7 +703,6 @@ usage:
 "                        change the root cgroup the controller will be\n"
 "                        installed into. No controller means that root is the\n"
 "                        default for all controllers not specified.\n"
-"  --cgroup-yard DIR     use DIR as premounted cgroups external yard\n"
 "  --skip-mnt PATH       ignore this mountpoint when dumping the mount namespace.\n"
 "  --enable-fs FSNAMES   a comma separated list of filesystem names or \"all\".\n"
 "                        force criu to (try to) dump/restore these filesystem's\n"

include/cr_options.h

@@ -72,7 +72,6 @@ struct cr_options {
 	bool			force_irmap;
 	char			**exec_cmd;
 	unsigned int		manage_cgroups;
-	char			*cg_yard;
 	char			*new_global_cg_root;
 	struct list_head	new_cgroup_roots;
 	bool			autodetect_ext_mounts;