From: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Date: Sun, 23 Apr 2023 11:16:48 +0000 (+0530)
Subject: api.c: add cgroup v2 support to cgroup_get_current_controller_path()
X-Git-Tag: v3.1.0~86
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=72ccaa389e874e70111f4a56330538441573c4e8;p=thirdparty%2Flibcgroup.git

api.c: add cgroup v2 support to cgroup_get_current_controller_path()

Add support to read/parse cgroup v2 format /proc/<pid>/cgroup to
cgroup_get_current_controller_path(). The format of /proc/<pid>/cgroup
remains the same:
hierarchy-ID:controller-list:cgroup-path

the difference is that in cgroup v2 mode:
- hierarchy-ID is always 0 (one hierarchy allowed)
- controller-list is empty

there can also be a mix of both legacy and unified controllers for a
given task if the cgroup mode is hybrid mode.  This patch, add support
for the mixed cgroup setup mode too.

Reported-by: Adriaan Schmidt <adriaan.schmidt@siemens.com>
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 941b0755..99ca01b8 100644
--- a/src/api.c
+++ b/src/api.c
@@ -4805,17 +4805,37 @@ int cgroup_init_rules_cache(void)
 int cgroup_get_current_controller_path(pid_t pid, const char *controller, char **current_path)
 {
 	FILE *pid_cgroup_fd = NULL;
+	enum cg_version_t version;
+	enum cg_setup_mode_t mode;
+	bool unified = false;
 	char *path = NULL;
 	int ret;
 
-	if (!controller)
-		return ECGOTHER;
-
 	if (!cgroup_initialized) {
 		cgroup_warn("libcgroup is not initialized\n");
 		return ECGROUPNOTINITIALIZED;
 	}
 
+	mode = cgroup_setup_mode();
+	if (mode == CGROUP_MODE_LEGACY && !controller)
+		return ECGOTHER;
+
+	/*
+	 * both unified/hybrid can have the controller mounted as
+	 * cgroup v2 version.
+	 */
+	if  (!controller) {
+		unified = true;
+	} else {
+		ret = cgroup_get_controller_version(controller, &version);
+		if (ret) {
+			cgroup_warn("Failed to get version of the controller: %s\n", controller);
+			ret = ECGINVAL;
+			goto cleanup_path;
+		}
+		unified = (version == CGROUP_V2);
+	}
+
 	ret = asprintf(&path, "/proc/%d/cgroup", pid);
 	if (ret <= 0) {
 		cgroup_warn("cannot allocate memory (/proc/pid/cgroup) ret %d\n", ret);
@@ -4842,6 +4862,49 @@ int cgroup_get_current_controller_path(pid_t pid, const char *controller, char *
 		char *token;
 		int num;
 
+		/*
+		 * with unified mode, the /proc/pid/cgroup the output is
+		 * similar to that of cgroup legacy and hybrid modes:
+		 * hierarchy-ID:controller-list:cgroup-path
+		 *
+		 * the difference is that in cgroup v2:
+		 * - hierarchy-ID is always 0 (one hierarchy allowed)
+		 * - controller-list is empty
+		 */
+		if (mode == CGROUP_MODE_UNIFIED || unified) {
+			ret = fscanf(pid_cgroup_fd, "%d::%4096s\n", &num, cgroup_path);
+			if (ret != 2) {
+				/*
+				 * we are interested only in unified format
+				 * line, skip this line.
+				 */
+				if (unified) {
+					fscanf(pid_cgroup_fd, "%*[^\n]\n");
+					continue;
+				}
+
+				cgroup_warn("read failed for pid_cgroup_fd ret %d\n", ret);
+				last_errno = errno;
+				ret = ECGOTHER;
+				goto done;
+			}
+
+			/* check if the controller is enabled in cgroup v2 */
+			if (controller) {
+				ret = cgroupv2_controller_enabled(cgroup_path, controller);
+				if (ret)
+					goto done;
+			}
+
+			*current_path = strdup(cgroup_path);
+			if (!*current_path) {
+				last_errno = errno;
+				ret = ECGOTHER;
+			}
+			ret = 0;
+			goto done;
+		}
+
 		/*
 		 * 4096 == FILENAME_MAX, keeping the coverity happy with precision
 		 * for the cgroup_path.