From 4c139a723040750f844b9bacb31176f819e4c9f8 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Sat, 14 Apr 2012 02:15:13 +0200
Subject: [PATCH] cgroup: if a controller is not available don't try to create
 cgroups in its hierarchy (cherry picked from commit
 3474ae3c7e1981301d0b35bc89d759ca13f06e8f)

---
 src/core/cgroup.c         |    6 ++--
 src/shared/cgroup-label.c |    3 +-
 src/shared/cgroup-util.c  |   82 +++++++++++++++++++++++++++++----------------
 src/shared/cgroup-util.h  |    1 +
 4 files changed, 61 insertions(+), 31 deletions(-)

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index a4eb6ed..6ae9f48 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -334,7 +334,8 @@ int manager_setup_cgroup(Manager *m) {
         }
 
         /* 2. Show data */
-        if ((r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, NULL, &path)) < 0) {
+        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;
         }
@@ -342,7 +343,8 @@ int manager_setup_cgroup(Manager *m) {
         log_debug("Using cgroup controller " SYSTEMD_CGROUP_CONTROLLER ". File system hierarchy is at %s.", path);
 
         /* 3. Install agent */
-        if ((r = cg_install_release_agent(SYSTEMD_CGROUP_CONTROLLER, SYSTEMD_CGROUP_AGENT_PATH)) < 0)
+        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.");
diff --git a/src/shared/cgroup-label.c b/src/shared/cgroup-label.c
index f9a42c6..3f00664 100644
--- a/src/shared/cgroup-label.c
+++ b/src/shared/cgroup-label.c
@@ -43,7 +43,8 @@ int cg_create(const char *controller, const char *path) {
         assert(controller);
         assert(path);
 
-        if ((r = cg_get_path(controller, path, NULL, &fs)) < 0)
+        r = cg_get_path_and_check(controller, path, NULL, &fs);
+        if (r < 0)
                 return r;
 
         r = mkdir_parents(fs, 0755);
diff --git a/src/shared/cgroup-util.c b/src/shared/cgroup-util.c
index ad677d4..6ae70f6 100644
--- a/src/shared/cgroup-util.c
+++ b/src/shared/cgroup-util.c
@@ -502,14 +502,47 @@ finish:
         return ret;
 }
 
+static const char *normalize_controller(const char *controller) {
+
+        if (streq(controller, SYSTEMD_CGROUP_CONTROLLER))
+                return "systemd";
+        else if (startswith(controller, "name="))
+                return controller + 5;
+        else
+                return controller;
+}
+
+static int join_path(const char *controller, const char *path, const char *suffix, char **fs) {
+        char *t;
+
+        if (path && suffix)
+                t = join("/sys/fs/cgroup/", controller, "/", path, "/", suffix, NULL);
+        else if (path)
+                t = join("/sys/fs/cgroup/", controller, "/", path, NULL);
+        else if (suffix)
+                t = join("/sys/fs/cgroup/", controller, "/", suffix, NULL);
+        else
+                t = join("/sys/fs/cgroup/", controller, NULL);
+
+        if (!t)
+                return -ENOMEM;
+
+        path_kill_slashes(t);
+
+        *fs = t;
+        return 0;
+}
+
 int cg_get_path(const char *controller, const char *path, const char *suffix, char **fs) {
         const char *p;
-        char *t;
         static __thread bool good = false;
 
         assert(controller);
         assert(fs);
 
+        if (isempty(controller))
+                return -EINVAL;
+
         if (_unlikely_(!good)) {
                 int r;
 
@@ -521,38 +554,30 @@ int cg_get_path(const char *controller, const char *path, const char *suffix, ch
                 good = true;
         }
 
-        if (isempty(controller))
-                return -EINVAL;
+        p = normalize_controller(controller);
 
-        /* This is a very minimal lookup from controller names to
-         * paths. Since we have mounted most hierarchies ourselves
-         * should be kinda safe, but eventually we might want to
-         * extend this to have a fallback to actually check
-         * /proc/mounts. Might need caching then. */
+        return join_path(p, path, suffix, fs);
+}
 
-        if (streq(controller, SYSTEMD_CGROUP_CONTROLLER))
-                p = "systemd";
-        else if (startswith(controller, "name="))
-                p = controller + 5;
-        else
-                p = controller;
+int cg_get_path_and_check(const char *controller, const char *path, const char *suffix, char **fs) {
+        const char *p;
+        char *cc;
 
-        if (path && suffix)
-                t = join("/sys/fs/cgroup/", p, "/", path, "/", suffix, NULL);
-        else if (path)
-                t = join("/sys/fs/cgroup/", p, "/", path, NULL);
-        else if (suffix)
-                t = join("/sys/fs/cgroup/", p, "/", suffix, NULL);
-        else
-                t = join("/sys/fs/cgroup/", p, NULL);
+        assert(controller);
+        assert(fs);
 
-        if (!t)
-                return -ENOMEM;
+        if (isempty(controller))
+                return -EINVAL;
 
-        path_kill_slashes(t);
+        p = normalize_controller(controller);
 
-        *fs = t;
-        return 0;
+        /* Check if this controller actually really exists */
+        cc = alloca(sizeof("/sys/fs/cgroup/") + strlen(p));
+        strcpy(stpcpy(cc, "/sys/fs/cgroup/"), p);
+        if (access(cc, F_OK) < 0)
+                return -errno;
+
+        return join_path(p, path, suffix, fs);
 }
 
 static int trim_cb(const char *path, const struct stat *sb, int typeflag, struct FTW *ftwbuf) {
@@ -646,7 +671,8 @@ int cg_attach(const char *controller, const char *path, pid_t pid) {
         assert(path);
         assert(pid >= 0);
 
-        if ((r = cg_get_path(controller, path, "tasks", &fs)) < 0)
+        r = cg_get_path_and_check(controller, path, "tasks", &fs);
+        if (r < 0)
                 return r;
 
         if (pid == 0)
diff --git a/src/shared/cgroup-util.h b/src/shared/cgroup-util.h
index 37e4255..1d1f93e 100644
--- a/src/shared/cgroup-util.h
+++ b/src/shared/cgroup-util.h
@@ -48,6 +48,7 @@ int cg_join_spec(const char *controller, const char *path, char **spec);
 int cg_fix_path(const char *path, char **result);
 
 int cg_get_path(const char *controller, const char *path, const char *suffix, char **fs);
+int cg_get_path_and_check(const char *controller, const char *path, const char *suffix, char **fs);
 int cg_get_by_pid(const char *controller, pid_t pid, char **path);
 
 int cg_trim(const char *controller, const char *path, bool delete_root);