From c2b1654c11313b9eec366239bc5108df7a5a051e Mon Sep 17 00:00:00 2001
From: Nikita Ioffe <ioffe@google.com>
Date: Thu, 20 Oct 2022 14:14:39 +0100
Subject: [PATCH] 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                                 |  4 +++
 init/service.cpp                              | 34 +++++++++++--------
 init/service_utils.cpp                        |  9 +++++
 .../include/processgroup/processgroup.h       |  1 +
 libprocessgroup/processgroup.cpp              |  5 +++
 5 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/init/init.cpp b/init/init.cpp
index cd0ee58ec..2d9fbbf3e 100644
--- a/init/init.cpp
+++ b/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);
diff --git a/init/service.cpp b/init/service.cpp
index a6330484a..24fcdce75 100644
--- a/init/service.cpp
+++ b/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) {
diff --git a/init/service_utils.cpp b/init/service_utils.cpp
index d19f5eef5..a14969e98 100644
--- a/init/service_utils.cpp
+++ b/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)) {
diff --git a/libprocessgroup/include/processgroup/processgroup.h b/libprocessgroup/include/processgroup/processgroup.h
index 45a723f74..9b2d77567 100644
--- a/libprocessgroup/include/processgroup/processgroup.h
+++ b/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);
diff --git a/libprocessgroup/processgroup.cpp b/libprocessgroup/processgroup.cpp
index bdda1020c..3fac373cb 100644
--- a/libprocessgroup/processgroup.cpp
+++ b/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);