core: always create /user and /machine top-level cgroup dirs

This allows clients to put inotify watches on these trees to watch for
state changes, without having to wait until these dirs are created.

This introduces the new top-level /machine cgroup dir as canonical
location where OS containers and VMs shall be located (as discussed with
the libvirt folks).

src/core/cgroup.c

@@ -40,7 +40,7 @@ int cgroup_bonding_realize(CGroupBonding *b) {
         assert(b->path);
         assert(b->controller);
 
-        r = cg_create(b->controller, b->path);
+        r = cg_create(b->controller, b->path, NULL);
         if (r < 0) {
                 log_warning("Failed to create cgroup %s:%s: %s", b->controller, b->path, strerror(-r));
                 return r;
@@ -319,9 +319,9 @@ int cgroup_bonding_is_empty_list(CGroupBonding *first) {
 }
 
 int manager_setup_cgroup(Manager *m) {
-        char *current = NULL, *path = NULL;
+        _cleanup_free_ char *current = NULL, *path = NULL;
         int r;
-        char suffix[32];
+        char suffix[sizeof("/systemd-") + DECIMAL_STR_MAX(pid_t)];
 
         assert(m);
 
@@ -335,7 +335,7 @@ int manager_setup_cgroup(Manager *m) {
         r = cg_get_by_pid(SYSTEMD_CGROUP_CONTROLLER, 0, &current);
         if (r < 0) {
                 log_error("Cannot determine cgroup we are running in: %s", strerror(-r));
-                goto finish;
+                return r;
         }
 
         if (m->running_as == SYSTEMD_SYSTEM)
@@ -354,35 +354,35 @@ int manager_setup_cgroup(Manager *m) {
         } else {
                 /* We need a new root cgroup */
                 m->cgroup_hierarchy = NULL;
-                if (asprintf(&m->cgroup_hierarchy, "%s%s", streq(current, "/") ? "" : current, suffix) < 0) {
-                        r = log_oom();
-                        goto finish;
-                }
+                if (asprintf(&m->cgroup_hierarchy, "%s%s", streq(current, "/") ? "" : current, suffix) < 0)
+                        return log_oom();
         }
 
         /* 2. Show data */
         r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, NULL, &path);
         if (r < 0) {
                 log_error("Cannot find cgroup mount point: %s", strerror(-r));
-                goto finish;
+                return r;
         }
 
         log_debug("Using cgroup controller " SYSTEMD_CGROUP_CONTROLLER ". File system hierarchy is at %s.", path);
 
         /* 3. Install agent */
-        r = cg_install_release_agent(SYSTEMD_CGROUP_CONTROLLER, SYSTEMD_CGROUP_AGENT_PATH);
-        if (r < 0)
-                log_warning("Failed to install release agent, ignoring: %s", strerror(-r));
-        else if (r > 0)
-                log_debug("Installed release agent.");
-        else
-                log_debug("Release agent already installed.");
+        if (m->running_as == SYSTEMD_SYSTEM) {
+                r = cg_install_release_agent(SYSTEMD_CGROUP_CONTROLLER, SYSTEMD_CGROUP_AGENT_PATH);
+                if (r < 0)
+                        log_warning("Failed to install release agent, ignoring: %s", strerror(-r));
+                else if (r > 0)
+                        log_debug("Installed release agent.");
+                else
+                        log_debug("Release agent already installed.");
+        }
 
         /* 4. Realize the group */
         r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, 0);
         if (r < 0) {
                 log_error("Failed to create root cgroup hierarchy: %s", strerror(-r));
-                goto finish;
+                return r;
         }
 
         /* 5. And pin it, so that it cannot be unmounted */
@@ -392,19 +392,21 @@ int manager_setup_cgroup(Manager *m) {
         m->pin_cgroupfs_fd = open(path, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOCTTY|O_NONBLOCK);
         if (r < 0) {
                 log_error("Failed to open pin file: %m");
-                r = -errno;
-                goto finish;
+                return -errno;
         }
 
-        log_debug("Created root group.");
-
+        /* 6. Remove non-existing controllers from the default controllers list */
         cg_shorten_controllers(m->default_controllers);
 
-finish:
-        free(current);
-        free(path);
+        /* 7. Let's create the user and machine hierarchies
+         * right-away, so that people can inotify on them, if they
+         * wish, without this being racy. */
+        if (m->running_as == SYSTEMD_SYSTEM) {
+                cg_create(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, "../user");
+                cg_create(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, "../machine");
+        }
 
-        return r;
+        return 0;
 }
 
 void manager_shutdown_cgroup(Manager *m, bool delete) {

src/login/logind-session.c

@@ -442,9 +442,9 @@ static int session_create_one_group(Session *s, const char *controller, const ch
         if (s->leader > 0) {
                 r = cg_create_and_attach(controller, path, s->leader);
                 if (r < 0)
-                        r = cg_create(controller, path);
+                        r = cg_create(controller, path, NULL);
         } else
-                r = cg_create(controller, path);
+                r = cg_create(controller, path, NULL);
 
         if (r < 0)
                 return r;

src/login/logind-user.c

@@ -320,7 +320,7 @@ static int user_create_cgroup(User *u) {
         } else
                 p = u->cgroup_path;
 
-        r = cg_create(SYSTEMD_CGROUP_CONTROLLER, p);
+        r = cg_create(SYSTEMD_CGROUP_CONTROLLER, p, NULL);
         if (r < 0) {
                 log_error("Failed to create cgroup "SYSTEMD_CGROUP_CONTROLLER":%s: %s", p, strerror(-r));
                 free(p);
@@ -335,7 +335,7 @@ static int user_create_cgroup(User *u) {
                 if (strv_contains(u->manager->reset_controllers, *k))
                         continue;
 
-                r = cg_create(*k, p);
+                r = cg_create(*k, p, NULL);
                 if (r < 0)
                         log_warning("Failed to create cgroup %s:%s: %s", *k, p, strerror(-r));
         }

src/shared/cgroup-label.c

@@ -36,14 +36,14 @@
 #include "util.h"
 #include "mkdir.h"
 
-int cg_create(const char *controller, const char *path) {
+int cg_create(const char *controller, const char *path, const char *suffix) {
         _cleanup_free_ char *fs = NULL;
         int r;
 
         assert(controller);
         assert(path);
 
-        r = cg_get_path_and_check(controller, path, NULL, &fs);
+        r = cg_get_path_and_check(controller, path, suffix, &fs);
         if (r < 0)
                 return r;
 
@@ -69,7 +69,7 @@ int cg_create_and_attach(const char *controller, const char *path, pid_t pid) {
         assert(path);
         assert(pid >= 0);
 
-        r = cg_create(controller, path);
+        r = cg_create(controller, path, NULL);
         if (r < 0)
                 return r;
 

src/shared/cgroup-util.h

@@ -55,7 +55,7 @@ int cg_trim(const char *controller, const char *path, bool delete_root);
 int cg_rmdir(const char *controller, const char *path, bool honour_sticky);
 int cg_delete(const char *controller, const char *path);
 
-int cg_create(const char *controller, const char *path);
+int cg_create(const char *controller, const char *path, const char *suffix);
 int cg_attach(const char *controller, const char *path, pid_t pid);
 int cg_create_and_attach(const char *controller, const char *path, pid_t pid);
 

src/test/test-cgroup.c

@@ -31,10 +31,10 @@ int main(int argc, char*argv[]) {
         char *path;
         char *c, *p;
 
-        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-a") == 0);
-        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-a") == 0);
-        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-b") == 0);
-        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-b/test-c") == 0);
+        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-a", NULL) == 0);
+        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-a", NULL) == 0);
+        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-b", NULL) == 0);
+        assert_se(cg_create(SYSTEMD_CGROUP_CONTROLLER, "/test-b/test-c", NULL) == 0);
         assert_se(cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, "/test-b", 0) == 0);
 
         assert_se(cg_get_by_pid(SYSTEMD_CGROUP_CONTROLLER, getpid(), &path) == 0);