core: update populated event handling in unified hierarchy

Earlier during the development of unified hierarchy, the populated event was
reported through by the dedicated "cgroup.populated" file; however, the
interface was updated so that it's reported through the "populated" field of
"cgroup.events" file.  Update populated event handling logic accordingly.

src/basic/cgroup-util.c

@@ -101,6 +101,39 @@ int cg_read_pid(FILE *f, pid_t *_pid) {
         return 1;
 }
 
+int cg_read_event(const char *controller, const char *path, const char *event,
+                  char **val)
+{
+        _cleanup_free_ char *events = NULL, *content = NULL;
+        char *p, *line;
+        int r;
+
+        r = cg_get_path(controller, path, "cgroup.events", &events);
+        if (r < 0)
+                return r;
+
+        r = read_full_file(events, &content, NULL);
+        if (r < 0)
+                return r;
+
+        p = content;
+        while ((line = strsep(&p, "\n"))) {
+                char *key;
+
+                key = strsep(&line, " ");
+                if (!key || !line)
+                        return -EINVAL;
+
+                if (strcmp(key, event))
+                        continue;
+
+                *val = strdup(line);
+                return 0;
+        }
+
+        return -ENOENT;
+}
+
 int cg_enumerate_subgroups(const char *controller, const char *path, DIR **_d) {
         _cleanup_free_ char *fs = NULL;
         int r;
@@ -1007,18 +1040,12 @@ int cg_is_empty_recursive(const char *controller, const char *path) {
                 return unified;
 
         if (unified > 0) {
-                _cleanup_free_ char *populated = NULL, *t = NULL;
+                _cleanup_free_ char *t = NULL;
 
                 /* On the unified hierarchy we can check empty state
-                 * via the "cgroup.populated" attribute. */
+                 * via the "populated" attribute of "cgroup.events". */
 
-                r = cg_get_path(controller, path, "cgroup.populated", &populated);
-                if (r < 0)
-                        return r;
-
-                r = read_one_line_file(populated, &t);
-                if (r == -ENOENT)
-                        return 1;
+                r = cg_read_event(controller, path, "populated", &t);
                 if (r < 0)
                         return r;
 

src/basic/cgroup-util.h

@@ -96,6 +96,8 @@ static inline bool CGROUP_BLKIO_WEIGHT_IS_OK(uint64_t x) {
 
 int cg_enumerate_processes(const char *controller, const char *path, FILE **_f);
 int cg_read_pid(FILE *f, pid_t *_pid);
+int cg_read_event(const char *controller, const char *path, const char *event,
+                  char **val);
 
 int cg_enumerate_subgroups(const char *controller, const char *path, DIR **_d);
 int cg_read_subgroup(DIR *d, char **fn);

src/core/cgroup.c

@@ -765,7 +765,7 @@ int unit_set_cgroup_path(Unit *u, const char *path) {
 }
 
 int unit_watch_cgroup(Unit *u) {
-        _cleanup_free_ char *populated = NULL;
+        _cleanup_free_ char *events = NULL;
         int r;
 
         assert(u);
@@ -791,11 +791,11 @@ int unit_watch_cgroup(Unit *u) {
         if (r < 0)
                 return log_oom();
 
-        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, "cgroup.populated", &populated);
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, "cgroup.events", &events);
         if (r < 0)
                 return log_oom();
 
-        u->cgroup_inotify_wd = inotify_add_watch(u->manager->cgroup_inotify_fd, populated, IN_MODIFY);
+        u->cgroup_inotify_wd = inotify_add_watch(u->manager->cgroup_inotify_fd, events, IN_MODIFY);
         if (u->cgroup_inotify_wd < 0) {
 
                 if (errno == ENOENT) /* If the directory is already

src/nspawn/nspawn-cgroup.c

@@ -55,8 +55,7 @@ int chown_cgroup(pid_t pid, uid_t uid_shift) {
                        "cgroup.events",
                        "cgroup.clone_children",
                        "cgroup.controllers",
-                       "cgroup.subtree_control",
-                       "cgroup.populated")
+                       "cgroup.subtree_control")
                 if (fchownat(fd, fn, uid_shift, uid_shift, 0) < 0)
                         log_full_errno(errno == ENOENT ? LOG_DEBUG :  LOG_WARNING, errno,
                                        "Failed to chown() cgroup file %s, ignoring: %m", fn);