From 7f19b1e6de17dd124328f7538e23d6bed56b55fc Mon Sep 17 00:00:00 2001
From: Suren Baghdasaryan <surenb@google.com>
Date: Wed, 10 Mar 2021 10:31:35 -0800
Subject: [PATCH] libprocessgroup: introduce optional attribute for cgroup
 controllers

Memory cgroup controller is not used by high-end Android devices and is
disabled in Android kernels 5.10+, however Android Go devices still
require this controller.
Similarly schedtune controller is being replaced with cpu controller's
utilclamp feature, however some devices are using older kernels which
only support schedtune.
To prevent spamming logcat with errors we need a way to mark a
controller optional in such cases without removing it from
cgroups.json file.
Introduce "Optional" attribute to cgroup controller's cgroups.json
description to accomodate these cases. When an optional controller
fails to mount due to lack of support in the kernel it will log an
informational message without generating further errors.

Bug: 181866655
Test: boot and observe libprocessgroup messages in logcat
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Ib5bcfdd8d338704f3f9d8b326d8ddd88b67915a1
---
 .../cgrouprc/include/android/cgrouprc.h           |  1 +
 libprocessgroup/profiles/cgroups.json             |  3 ++-
 libprocessgroup/profiles/cgroups.proto            |  3 ++-
 libprocessgroup/profiles/cgroups_30.json          |  3 ++-
 libprocessgroup/setup/cgroup_map_write.cpp        | 15 +++++++++++++--
 5 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/libprocessgroup/cgrouprc/include/android/cgrouprc.h b/libprocessgroup/cgrouprc/include/android/cgrouprc.h
index 9a799547d..100d60ea9 100644
--- a/libprocessgroup/cgrouprc/include/android/cgrouprc.h
+++ b/libprocessgroup/cgrouprc/include/android/cgrouprc.h
@@ -68,6 +68,7 @@ __attribute__((warn_unused_result)) uint32_t ACgroupController_getVersion(const
  */
 #define CGROUPRC_CONTROLLER_FLAG_MOUNTED 0x1
 #define CGROUPRC_CONTROLLER_FLAG_NEEDS_ACTIVATION 0x2
+#define CGROUPRC_CONTROLLER_FLAG_OPTIONAL 0x4
 
 /**
  * Returns the flags bitmask of the given controller.
diff --git a/libprocessgroup/profiles/cgroups.json b/libprocessgroup/profiles/cgroups.json
index 962d2baa8..063422091 100644
--- a/libprocessgroup/profiles/cgroups.json
+++ b/libprocessgroup/profiles/cgroups.json
@@ -26,7 +26,8 @@
       "Path": "/dev/memcg",
       "Mode": "0700",
       "UID": "root",
-      "GID": "system"
+      "GID": "system",
+      "Optional": true
     }
   ],
   "Cgroups2": {
diff --git a/libprocessgroup/profiles/cgroups.proto b/libprocessgroup/profiles/cgroups.proto
index 13adcae07..f2de3452a 100644
--- a/libprocessgroup/profiles/cgroups.proto
+++ b/libprocessgroup/profiles/cgroups.proto
@@ -24,7 +24,7 @@ message Cgroups {
     Cgroups2 cgroups2 = 2 [json_name = "Cgroups2"];
 }
 
-// Next: 7
+// Next: 8
 message Cgroup {
     string controller = 1 [json_name = "Controller"];
     string path = 2 [json_name = "Path"];
@@ -35,6 +35,7 @@ message Cgroup {
 // when a boolean is specified as false, so leave unspecified in that case
 // https://developers.google.com/protocol-buffers/docs/proto3#default
     bool needs_activation = 6 [json_name = "NeedsActivation"];
+    bool is_optional = 7 [json_name = "Optional"];
 }
 
 // Next: 6
diff --git a/libprocessgroup/profiles/cgroups_30.json b/libprocessgroup/profiles/cgroups_30.json
index 17d492949..80a074bf1 100644
--- a/libprocessgroup/profiles/cgroups_30.json
+++ b/libprocessgroup/profiles/cgroups_30.json
@@ -5,7 +5,8 @@
       "Path": "/dev/stune",
       "Mode": "0755",
       "UID": "system",
-      "GID": "system"
+      "GID": "system",
+      "Optional": true
     }
   ]
 }
diff --git a/libprocessgroup/setup/cgroup_map_write.cpp b/libprocessgroup/setup/cgroup_map_write.cpp
index b0b91f81f..3121d244b 100644
--- a/libprocessgroup/setup/cgroup_map_write.cpp
+++ b/libprocessgroup/setup/cgroup_map_write.cpp
@@ -161,6 +161,10 @@ static void MergeCgroupToDescriptors(std::map<std::string, CgroupDescriptor>* de
         controller_flags |= CGROUPRC_CONTROLLER_FLAG_NEEDS_ACTIVATION;
     }
 
+    if (cgroup["Optional"].isBool() && cgroup["Optional"].asBool()) {
+        controller_flags |= CGROUPRC_CONTROLLER_FLAG_OPTIONAL;
+    }
+
     CgroupDescriptor descriptor(
             cgroups_version, name, path, std::strtoul(cgroup["Mode"].asString().c_str(), 0, 8),
             cgroup["UID"].asString(), cgroup["GID"].asString(), controller_flags);
@@ -308,8 +312,15 @@ static bool SetupCgroup(const CgroupDescriptor& descriptor) {
     }
 
     if (result < 0) {
-        PLOG(ERROR) << "Failed to mount " << controller->name() << " cgroup";
-        return false;
+        bool optional = controller->flags() & CGROUPRC_CONTROLLER_FLAG_OPTIONAL;
+
+        if (optional && errno == EINVAL) {
+            // Optional controllers are allowed to fail to mount if kernel does not support them
+            LOG(INFO) << "Optional " << controller->name() << " cgroup controller is not mounted";
+        } else {
+            PLOG(ERROR) << "Failed to mount " << controller->name() << " cgroup";
+            return false;
+        }
     }
 
     return true;