From: Tom Hromatka <tom.hromatka@oracle.com>
Date: Tue, 21 Feb 2023 21:17:58 +0000 (-0700)
Subject: api: Don't return an error when no cgroups are enabled
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=279187d7d39b2be0f86069e6b8d63cc29809309d;p=thirdparty%2Flibcgroup.git

api: Don't return an error when no cgroups are enabled

Don't return an error, ECGROUPNOTEXIST (50002), from cgroup_get_cgroup()
when no controllers are enabled in a cgroup v2 cgroup.

Simple reproducer:
	sudo mkdir -p /sys/fs/cgroup/foo/bar

	#!/usr/bin/env python3
	from libcgroup import Cgroup, Version

	cg = Cgroup('foo/bar', Version.CGROUP_V2)
	cg.get()
	print(cg)

Prior to this change, the above python code returned ECGROUPNOTEXIST in
the cg.get() line.  Now it successfully completes, but no controllers
are populated.

Reported-by: Justin Israel <justinisrael@gmail.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
(cherry picked from commit 7c99c8a385c5946c8873313b8c99cc9b5cf25bfd)
---

diff --git a/src/api.c b/src/api.c
index a944b73a..ad08bd37 100644
--- a/src/api.c
+++ b/src/api.c
@@ -3552,6 +3552,7 @@ int cgroup_get_cgroup(struct cgroup *cgroup)
 {
 	struct dirent *ctrl_dir = NULL;
 	int initial_controller_cnt;
+	int controller_cnt = 0;
 	char *control_path = NULL;
 	char path[FILENAME_MAX];
 	DIR *dir = NULL;
@@ -3644,8 +3645,10 @@ int cgroup_get_cgroup(struct cgroup *cgroup)
 				 * and we've made it this far, then they are explicitly
 				 * interested in this controller and we should not remove it.
 				 */
-				if (initial_controller_cnt == 0)
+				if (initial_controller_cnt == 0) {
+					controller_cnt++;
 					continue;
+				}
 			} else if (error) {
 				goto unlock_error;
 			}
@@ -3667,6 +3670,8 @@ int cgroup_get_cgroup(struct cgroup *cgroup)
 			goto unlock_error;
 		}
 
+		controller_cnt++;
+
 		while ((ctrl_dir = readdir(dir)) != NULL) {
 			/* Skip over non regular files */
 			if (ctrl_dir->d_type != DT_REG)
@@ -3707,8 +3712,14 @@ int cgroup_get_cgroup(struct cgroup *cgroup)
 		}
 	}
 
-	/* Check if the group really exists or not */
-	if (!cgroup->index) {
+	/*
+	 * Check if the group really exists or not.  The cgroup->index controller count can't
+	 * be used in this case because cgroup v2 allows controllers to be enabled/disabled in
+	 * the subtree_control file.  Rather, cgroup_get_cgroup() tracks the number of possible
+	 * controllers in the controller_cnt variable and uses that to determine if the cgroup
+	 * exists or not.
+	 */
+	if (!controller_cnt) {
 		error = ECGROUPNOTEXIST;
 		goto unlock_error;
 	}