init: skip cgroup/task_profiles configuration if cgroups are disabled

We are planning to remove cgroups from the Micrdroid kernel, since the
entire VM belongs exclusively to a single owner, and is in the control
of the cgroups on the host side.

This patch expoxes CgroupAvailable API from libprocessgroup, and changes
init to query the CgroupAvailable API before doing any
cgroups/task_profiles related work.

Bug: 239367015
Test: run MicrodroidDemoApp
Test: atest --test-mapping packages/modules/Virtualization:avf-presubmit
Change-Id: I82787141cd2a7f9309a4e9b24acbd92ca21c145b

init/init.cpp

@@ -662,6 +662,10 @@ static Result<void> wait_for_coldboot_done_action(const BuiltinArguments& args)
 }
 
 static Result<void> SetupCgroupsAction(const BuiltinArguments&) {
+    if (!CgroupsAvailable()) {
+        LOG(INFO) << "Cgroups support in kernel is not enabled";
+        return {};
+    }
     // Have to create <CGROUPS_RC_DIR> using make_dir function
     // for appropriate sepolicy to be set for it
     make_dir(android::base::Dirname(CGROUPS_RC_PATH), 0711);

init/service.cpp

@@ -682,24 +682,28 @@ Result<void> Service::Start() {
     start_order_ = next_start_order_++;
     process_cgroup_empty_ = false;
 
-    bool use_memcg = swappiness_ != -1 || soft_limit_in_bytes_ != -1 || limit_in_bytes_ != -1 ||
-                      limit_percent_ != -1 || !limit_property_.empty();
-    errno = -createProcessGroup(proc_attr_.uid, pid_, use_memcg);
-    if (errno != 0) {
-        if (char byte = 0; write((*pipefd)[1], &byte, 1) < 0) {
-            return ErrnoError() << "sending notification failed";
+    if (CgroupsAvailable()) {
+        bool use_memcg = swappiness_ != -1 || soft_limit_in_bytes_ != -1 || limit_in_bytes_ != -1 ||
+                         limit_percent_ != -1 || !limit_property_.empty();
+        errno = -createProcessGroup(proc_attr_.uid, pid_, use_memcg);
+        if (errno != 0) {
+            if (char byte = 0; write((*pipefd)[1], &byte, 1) < 0) {
+                return ErrnoError() << "sending notification failed";
+            }
+            return Error() << "createProcessGroup(" << proc_attr_.uid << ", " << pid_
+                           << ") failed for service '" << name_ << "'";
         }
-        return Error() << "createProcessGroup(" << proc_attr_.uid << ", " << pid_
-                       << ") failed for service '" << name_ << "'";
-    }
 
-    // When the blkio controller is mounted in the v1 hierarchy, NormalIoPriority is
-    // the default (/dev/blkio). When the blkio controller is mounted in the v2 hierarchy, the
-    // NormalIoPriority profile has to be applied explicitly.
-    SetProcessProfiles(proc_attr_.uid, pid_, {"NormalIoPriority"});
+        // When the blkio controller is mounted in the v1 hierarchy, NormalIoPriority is
+        // the default (/dev/blkio). When the blkio controller is mounted in the v2 hierarchy, the
+        // NormalIoPriority profile has to be applied explicitly.
+        SetProcessProfiles(proc_attr_.uid, pid_, {"NormalIoPriority"});
 
-    if (use_memcg) {
-        ConfigureMemcg();
+        if (use_memcg) {
+            ConfigureMemcg();
+        }
+    } else {
+        process_cgroup_empty_ = true;
     }
 
     if (oom_score_adjust_ != DEFAULT_OOM_SCORE_ADJUST) {

init/service_utils.cpp

@@ -280,6 +280,15 @@ Result<void> SetProcessAttributes(const ProcessAttributes& attr) {
 }
 
 Result<void> WritePidToFiles(std::vector<std::string>* files) {
+    if (files->empty()) {
+        // No files to write pid to, exit early.
+        return {};
+    }
+
+    if (!CgroupsAvailable()) {
+        return Error() << "cgroups are not available";
+    }
+
     // See if there were "writepid" instructions to write to files under cpuset path.
     std::string cpuset_path;
     if (CgroupGetControllerPath("cpuset", &cpuset_path)) {

libprocessgroup/include/processgroup/processgroup.h

@@ -28,6 +28,7 @@ __BEGIN_DECLS
 
 static constexpr const char* CGROUPV2_CONTROLLER_NAME = "cgroup2";
 
+bool CgroupsAvailable();
 bool CgroupGetControllerPath(const std::string& cgroup_name, std::string* path);
 bool CgroupGetControllerFromPath(const std::string& path, std::string* cgroup_name);
 bool CgroupGetAttributePath(const std::string& attr_name, std::string* path);

libprocessgroup/processgroup.cpp

@@ -55,6 +55,11 @@ using namespace std::chrono_literals;
 
 #define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"
 
+bool CgroupsAvailable() {
+    static bool cgroups_available = access("/proc/cgroups", F_OK) == 0;
+    return cgroups_available;
+}
+
 bool CgroupGetControllerPath(const std::string& cgroup_name, std::string* path) {
     auto controller = CgroupMap::GetInstance().FindController(cgroup_name);