cgroup: allow to specify a new root for each controller separately

A few controllers can be merged and before this patch, criu required to
set a new root by specifying all merged controllers.

This patch allows to specify a new root for each controller separately,
but criu will check that all merged controllers will have the same path.

https://github.com/checkpoint-restore/criu/issues/544Signed-off-by: Andrei Vagin <avagin@gmail.com>

criu/cgroup.c

@@ -186,7 +186,8 @@ int parse_cg_info(void)
 /* Check that co-mounted controllers from /proc/cgroups (e.g. cpu and cpuacct)
  * are contained in a comma separated string (e.g. from /proc/self/cgroup or
  * mount options). */
-static bool cgroup_contains(char **controllers, unsigned int n_controllers, char *name)
+static bool cgroup_contains(char **controllers,
+			unsigned int n_controllers, char *name, u64 *mask)
 {
 	unsigned int i;
 	bool all_match = true;
@@ -201,6 +202,8 @@ static bool cgroup_contains(char **controllers, unsigned int n_controllers, char
 				case '\0':
 				case ',':
 					found = true;
+					if (mask)
+						*mask &= ~(1ULL << i);
 					break;
 				}
 			}
@@ -557,7 +560,7 @@ static int collect_cgroups(struct list_head *ctls)
 		 * controller from parse_cgroups(), so find that controller if
 		 * it exists. */
 		list_for_each_entry(cg, &cgroups, l) {
-			if (cgroup_contains(cg->controllers, cg->n_controllers, cc->name)) {
+			if (cgroup_contains(cg->controllers, cg->n_controllers, cc->name, NULL)) {
 				current_controller = cg;
 				break;
 			}
@@ -1021,7 +1024,7 @@ static int prepare_cgns(CgSetEntry *se)
 
 		for (j = 0; j < n_controllers; j++) {
 			CgControllerEntry *cur = controllers[j];
-			if (cgroup_contains(cur->cnames, cur->n_cnames, ce->name)) {
+			if (cgroup_contains(cur->cnames, cur->n_cnames, ce->name, NULL)) {
 				ctrl = cur;
 				break;
 			}
@@ -1093,7 +1096,7 @@ static int move_in_cgroup(CgSetEntry *se, bool setup_cgns)
 
 		for (j = 0; j < n_controllers; j++) {
 			CgControllerEntry *cur = controllers[j];
-			if (cgroup_contains(cur->cnames, cur->n_cnames, ce->name)) {
+			if (cgroup_contains(cur->cnames, cur->n_cnames, ce->name, NULL)) {
 				ctrl = cur;
 				break;
 			}
@@ -1758,7 +1761,7 @@ static int rewrite_cgsets(CgroupEntry *cge, char **controllers, int n_controller
 			 * and its path with stripping leading
 			 * "/" is matching to be renamed.
 			 */
-			if (!(cgroup_contains(controllers, n_controllers, cg->name) &&
+			if (!(cgroup_contains(controllers, n_controllers, cg->name, NULL) &&
 					strstartswith(cg->path + 1, dir)))
 				continue;
 
@@ -1813,19 +1816,31 @@ static int rewrite_cgroup_roots(CgroupEntry *cge)
 {
 	int i, j;
 	struct cg_root_opt *o;
-	char *newroot = NULL;
 
 	for (i = 0; i < cge->n_controllers; i++) {
 		CgControllerEntry *ctrl = cge->controllers[i];
-		newroot = opts.new_global_cg_root;
+		u64 ctrl_mask = (1ULL << ctrl->n_cnames) - 1;
+		char *newroot = NULL;
 
 		list_for_each_entry(o, &opts.new_cgroup_roots, node) {
-			if (cgroup_contains(ctrl->cnames, ctrl->n_cnames, o->controller)) {
+			unsigned old_mask = ctrl_mask;
+
+			cgroup_contains(ctrl->cnames, ctrl->n_cnames,
+					o->controller, &ctrl_mask);
+			if (old_mask != ctrl_mask) {
+				if (newroot && strcmp(newroot, o->newroot)) {
+					pr_err("CG paths mismatch: %s %s\n",
+							newroot, o->newroot);
+					return -1;
+				}
 				newroot = o->newroot;
+			}
+			if (!ctrl_mask)
 				break;
 		}
 
-		}
+		if (!newroot)
+			newroot = opts.new_global_cg_root;
 
 		if (newroot) {
 			for (j = 0; j < ctrl->n_dirs; j++) {