[lxc-devel] [PATCH 1/1] cgroupfs: support older kernels without cgroup.clone_children

[Serge Hallyn]

When creating a cgroup, detect whether cgroup.clone_children
exists.  If not, then manually copy the parent's cpuset.cpus
and cpuset.mems values.

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/cgroup.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/src/lxc/cgroup.c b/src/lxc/cgroup.c
index 4482b32..49f1ba1 100644
--- a/src/lxc/cgroup.c
+++ b/src/lxc/cgroup.c
@@ -74,6 +74,7 @@ static int do_setup_cgroup_limits(struct lxc_handler *h, struct lxc_list *cgroup
 static int cgroup_recursive_task_count(const char *cgroup_path);
 static int count_lines(const char *fn);
 static int handle_cgroup_settings(struct cgroup_mount_point *mp, char *cgroup_path);
+static void setup_cpuset_if_needed(char **subsystems, char *path);
 
 static struct cgroup_ops cgfs_ops;
 struct cgroup_ops *active_cg_ops = &cgfs_ops;
@@ -723,6 +724,71 @@ static char *cgroup_rename_nsgroup(const char *mountpath, const char *oldname, p
 	return newname;
 }
 
+static long get_value(const char *dir, const char *file)
+{
+	FILE *f;
+	char path[MAXPATHLEN];
+	int ret, retv;
+
+	retv = snprintf(path, MAXPATHLEN, "%s/%s", dir, file);
+	if (retv < 0 || retv >= MAXPATHLEN)
+		return 0;
+	f = fopen(path, "r");
+	ret = fscanf(f, "%d", &retv);
+	fclose(f);
+	if (ret != 1)
+		return 0;
+	return retv;
+}
+
+static void set_value(const char *dir, const char *file, long v)
+{
+	FILE *f;
+	char path[MAXPATHLEN];
+	int retv;
+
+	retv = snprintf(path, MAXPATHLEN, "%s/%s", dir, file);
+	if (retv < 0 || retv >= MAXPATHLEN)
+		return;
+	f = fopen(path, "w");
+	fprintf(f, "%ld\n", v);
+	fclose(f);
+}
+
+static bool file_exists(const char *dir, const char *file)
+{
+	char path[MAXPATHLEN];
+	struct stat sb;
+	int ret;
+
+	ret = snprintf(path, MAXPATHLEN, "%s/%s", dir, file);
+	if (ret < 0 || ret >= MAXPATHLEN)
+		return true;
+	ret = stat(path, &sb);
+	return ret == 0;
+}
+
+static void setup_cpuset_if_needed(char **subsystems, char *path)
+{
+	char *parentpath, *p;
+	long v;
+	
+	if (!lxc_string_in_array("cpuset", (const char **) subsystems))
+		return;
+	if (file_exists(path, "cgroup.clone_children"))
+		return;
+	parentpath = strdup(path);
+	if (!parentpath)
+		return;
+	if ((p = rindex(parentpath, '/')))
+		*p = '\0';
+	v = get_value(parentpath, "cpuset.mems");
+	set_value(path, "cpuset.mems", v);
+	v = get_value(parentpath, "cpuset.cpus");
+	set_value(path, "cpuset.cpus", v);
+	free(parentpath);
+}
+
 /* create a new cgroup */
 struct cgroup_process_info *lxc_cgroupfs_create(const char *name, const char *path_pattern, struct cgroup_meta_data *meta_data, const char *sub_pattern)
 {
@@ -898,6 +964,8 @@ struct cgroup_process_info *lxc_cgroupfs_create(const char *name, const char *pa
 				if (r < 0)
 					goto cleanup_from_error;
 				info_ptr->created_paths[info_ptr->created_paths_count++] = current_entire_path;
+				setup_cpuset_if_needed(info_ptr->hierarchy->subsystems,
+						current_entire_path);
 			} else {
 				/* if we didn't create the cgroup, then we have to make sure that
 				 * further cgroups will be created properly
@@ -2039,8 +2107,12 @@ static int handle_cgroup_settings(struct cgroup_mount_point *mp,
 	 */
 	if (lxc_string_in_array("cpuset", (const char **)mp->hierarchy->subsystems)) {
 		char *cc_path = cgroup_to_absolute_path(mp, cgroup_path, "/cgroup.clone_children");
+		struct stat sb;
+
 		if (!cc_path)
 			return -1;
+		if (stat(cc_path, &sb) != 0 && errno == ENOENT)
+			return 0;
 		r = lxc_read_from_file(cc_path, buf, 1);
 		if (r == 1 && buf[0] == '1') {
 			free(cc_path);
-- 
1.8.5.3