From: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Date: Mon, 4 Apr 2022 06:48:46 +0000 (+0530)
Subject: api.c: add support to attach tid to an empty cgroup v2
X-Git-Tag: v3.0~90
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fb8a49dc5551165716ff368df593a91b4f422e0d;p=thirdparty%2Flibcgroup.git

api.c: add support to attach tid to an empty cgroup v2

Currently, cgroup_attach_task_pid() checks for enabled
controllers before attaching the given tid to it, but in the case of
empty cgroup, it simply ignores the attaching due to no controllers
available, a.k.a. cgroup->index is 0.  Add support to recognize empty
controller cgroups.

Fixes: https://github.com/libcgroup/libcgroup/issues/129

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
---

diff --git a/src/api.c b/src/api.c
index f5b6d303..7f244315 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1858,6 +1858,8 @@ err:
 int cgroup_attach_task_pid(struct cgroup *cgroup, pid_t tid)
 {
 	char path[FILENAME_MAX] = {0};
+	char *controller_name;
+	int empty_cgroup = 0;
 	int i, ret = 0;
 
 	if (!cgroup_initialized) {
@@ -1896,15 +1898,24 @@ int cgroup_attach_task_pid(struct cgroup *cgroup, pid_t tid)
 			}
 		}
 
-		for (i = 0; i < cgroup->index; i++) {
+		if (cgroup->index == 0)
+			/* Valid empty cgroup v2 with no controllers added. */
+			empty_cgroup = 1;
+
+		for (i = 0, controller_name = NULL;
+		     empty_cgroup > 0 || i < cgroup->index;
+		     i++, empty_cgroup--) {
+
+			if (cgroup->controller[i])
+				controller_name = cgroup->controller[i]->name;
+
 			ret = cgroupv2_controller_enabled(cgroup->name,
-				cgroup->controller[i]->name);
+						          controller_name);
 			if (ret)
 				return ret;
 
 			ret = cgroup_build_tasks_procs_path(path,
-				sizeof(path), cgroup->name,
-				cgroup->controller[i]->name);
+				sizeof(path), cgroup->name, controller_name);
 			if (ret)
 				return ret;