libprocessgroup: add flags to indicate when a controller failed to mount

Controllers listed in cgroups.json file might fail to mount if kernel is
not configured to support them. We need a way to indicate whether a
controller was successfully mounted and is usable to avoid logging errors
and warnings when a controller that failed to mount is being used. Add
flags bitmask to cgrouprc controller descriptor and use a bit to indicate
that controller is successfully mounted. Modify cpusets_enabled() and
schedboost_enabled() functions to use this bit and report the actual
availability of the controller.

Bug: 124080437
Test: libcutils_test with cpuset and schedtune controllers disabled
Change-Id: I770cc39fe50465146e3205aacf77dc3c56923c5d
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

libprocessgroup/cgroup_map.cpp

@@ -67,6 +67,13 @@ bool CgroupController::HasValue() const {
     return controller_ != nullptr;
 }
 
+bool CgroupController::IsUsable() const {
+    if (!HasValue()) return false;
+
+    uint32_t flags = ACgroupController_getFlags(controller_);
+    return (flags & CGROUPRC_CONTROLLER_FLAG_MOUNTED) != 0;
+}
+
 std::string CgroupController::GetTasksFilePath(const std::string& rel_path) const {
     std::string tasks_path = path();
 
@@ -153,6 +160,7 @@ void CgroupMap::Print() const {
         const ACgroupController* controller = ACgroupFile_getController(i);
         LOG(INFO) << "\t" << ACgroupController_getName(controller) << " ver "
                   << ACgroupController_getVersion(controller) << " path "
+                  << ACgroupController_getFlags(controller) << " flags "
                   << ACgroupController_getPath(controller);
     }
 }

libprocessgroup/cgroup_map.h

@@ -38,6 +38,7 @@ class CgroupController {
     const char* path() const;
 
     bool HasValue() const;
+    bool IsUsable() const;
 
     std::string GetTasksFilePath(const std::string& path) const;
     std::string GetProcsFilePath(const std::string& path, uid_t uid, pid_t pid) const;

libprocessgroup/cgrouprc/Android.bp

@@ -42,19 +42,19 @@ cc_library {
         "libcgrouprc_format",
     ],
     stubs: {
-        symbol_file: "libcgrouprc.map.txt",
+        symbol_file: "libcgrouprc.llndk.txt",
         versions: ["29"],
     },
     target: {
         linux: {
-            version_script: "libcgrouprc.map.txt",
+            version_script: "libcgrouprc.llndk.txt",
         },
     },
 }
 
 llndk_library {
     name: "libcgrouprc",
-    symbol_file: "libcgrouprc.map.txt",
+    symbol_file: "libcgrouprc.llndk.txt",
     export_include_dirs: [
         "include",
     ],

libprocessgroup/cgrouprc/cgroup_controller.cpp

@@ -27,6 +27,11 @@ uint32_t ACgroupController_getVersion(const ACgroupController* controller) {
     return controller->version();
 }
 
+uint32_t ACgroupController_getFlags(const ACgroupController* controller) {
+    CHECK(controller != nullptr);
+    return controller->flags();
+}
+
 const char* ACgroupController_getName(const ACgroupController* controller) {
     CHECK(controller != nullptr);
     return controller->name();

libprocessgroup/cgrouprc/include/android/cgrouprc.h

@@ -65,6 +65,18 @@ __attribute__((warn_unused_result)) const ACgroupController* ACgroupFile_getCont
 __attribute__((warn_unused_result)) uint32_t ACgroupController_getVersion(const ACgroupController*)
         __INTRODUCED_IN(29);
 
+/**
+ * Flag bitmask used in ACgroupController_getFlags
+ */
+#define CGROUPRC_CONTROLLER_FLAG_MOUNTED 0x1
+
+/**
+ * Returns the flags bitmask of the given controller.
+ * If the given controller is null, return 0.
+ */
+__attribute__((warn_unused_result)) uint32_t ACgroupController_getFlags(const ACgroupController*)
+        __INTRODUCED_IN(29);
+
 /**
  * Returns the name of the given controller.
  * If the given controller is null, return nullptr.

libprocessgroup/cgrouprc/libcgrouprc.llndk.txt

@@ -4,6 +4,7 @@ LIBCGROUPRC { # introduced=29
     ACgroupFile_getControllerCount;
     ACgroupFile_getController;
     ACgroupController_getVersion;
+    ACgroupController_getFlags;
     ACgroupController_getName;
     ACgroupController_getPath;
   local:

libprocessgroup/cgrouprc_format/cgroup_controller.cpp

@@ -20,12 +20,19 @@ namespace android {
 namespace cgrouprc {
 namespace format {
 
-CgroupController::CgroupController(uint32_t version, const std::string& name,
-                                   const std::string& path) {
+CgroupController::CgroupController() : version_(0), flags_(0) {
+    memset(name_, 0, sizeof(name_));
+    memset(path_, 0, sizeof(path_));
+}
+
+CgroupController::CgroupController(uint32_t version, uint32_t flags, const std::string& name,
+                                   const std::string& path)
+    : CgroupController() {
     // strlcpy isn't available on host. Although there is an implementation
     // in licutils, libcutils itself depends on libcgrouprc_format, causing
     // a circular dependency.
     version_ = version;
+    flags_ = flags;
     strncpy(name_, name.c_str(), sizeof(name_) - 1);
     name_[sizeof(name_) - 1] = '\0';
     strncpy(path_, path.c_str(), sizeof(path_) - 1);
@@ -36,6 +43,10 @@ uint32_t CgroupController::version() const {
     return version_;
 }
 
+uint32_t CgroupController::flags() const {
+    return flags_;
+}
+
 const char* CgroupController::name() const {
     return name_;
 }
@@ -44,6 +55,10 @@ const char* CgroupController::path() const {
     return path_;
 }
 
+void CgroupController::set_flags(uint32_t flags) {
+    flags_ = flags;
+}
+
 }  // namespace format
 }  // namespace cgrouprc
 }  // namespace android

libprocessgroup/cgrouprc_format/include/processgroup/format/cgroup_controller.h

@@ -26,18 +26,23 @@ namespace format {
 // Minimal controller description to be mmapped into process address space
 struct CgroupController {
   public:
-    CgroupController() {}
-    CgroupController(uint32_t version, const std::string& name, const std::string& path);
+    CgroupController();
+    CgroupController(uint32_t version, uint32_t flags, const std::string& name,
+                     const std::string& path);
 
     uint32_t version() const;
+    uint32_t flags() const;
     const char* name() const;
     const char* path() const;
 
+    void set_flags(uint32_t flags);
+
   private:
     static constexpr size_t CGROUP_NAME_BUF_SZ = 16;
     static constexpr size_t CGROUP_PATH_BUF_SZ = 32;
 
     uint32_t version_;
+    uint32_t flags_;
     char name_[CGROUP_NAME_BUF_SZ];
     char path_[CGROUP_PATH_BUF_SZ];
 };

libprocessgroup/processgroup.cpp

@@ -106,8 +106,7 @@ bool UsePerAppMemcg() {
 }
 
 static bool isMemoryCgroupSupported() {
-    std::string cgroup_name;
-    static bool memcg_supported = CgroupMap::GetInstance().FindController("memory").HasValue();
+    static bool memcg_supported = CgroupMap::GetInstance().FindController("memory").IsUsable();
 
     return memcg_supported;
 }

libprocessgroup/sched_policy.cpp

@@ -151,19 +151,19 @@ int set_sched_policy(int tid, SchedPolicy policy) {
 }
 
 bool cpusets_enabled() {
-    static bool enabled = (CgroupMap::GetInstance().FindController("cpuset").HasValue());
+    static bool enabled = (CgroupMap::GetInstance().FindController("cpuset").IsUsable());
     return enabled;
 }
 
 bool schedboost_enabled() {
-    static bool enabled = (CgroupMap::GetInstance().FindController("schedtune").HasValue());
+    static bool enabled = (CgroupMap::GetInstance().FindController("schedtune").IsUsable());
     return enabled;
 }
 
 static int getCGroupSubsys(int tid, const char* subsys, std::string& subgroup) {
     auto controller = CgroupMap::GetInstance().FindController(subsys);
 
-    if (!controller.HasValue()) return -1;
+    if (!controller.IsUsable()) return -1;
 
     if (!controller.GetTaskGroup(tid, &subgroup)) {
         LOG(ERROR) << "Failed to find cgroup for tid " << tid;

libprocessgroup/setup/cgroup_descriptor.h

@@ -32,6 +32,8 @@ class CgroupDescriptor {
     std::string uid() const { return uid_; }
     std::string gid() const { return gid_; }
 
+    void set_mounted(bool mounted);
+
   private:
     format::CgroupController controller_;
     mode_t mode_ = 0;

libprocessgroup/setup/cgroup_map_write.cpp

@@ -35,6 +35,7 @@
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/unique_fd.h>
+#include <android/cgrouprc.h>
 #include <json/reader.h>
 #include <json/value.h>
 #include <processgroup/format/cgroup_file.h>
@@ -267,7 +268,17 @@ static bool WriteRcFile(const std::map<std::string, CgroupDescriptor>& descripto
 CgroupDescriptor::CgroupDescriptor(uint32_t version, const std::string& name,
                                    const std::string& path, mode_t mode, const std::string& uid,
                                    const std::string& gid)
-    : controller_(version, name, path), mode_(mode), uid_(uid), gid_(gid) {}
+    : controller_(version, 0, name, path), mode_(mode), uid_(uid), gid_(gid) {}
+
+void CgroupDescriptor::set_mounted(bool mounted) {
+    uint32_t flags = controller_.flags();
+    if (mounted) {
+        flags |= CGROUPRC_CONTROLLER_FLAG_MOUNTED;
+    } else {
+        flags &= ~CGROUPRC_CONTROLLER_FLAG_MOUNTED;
+    }
+    controller_.set_flags(flags);
+}
 
 }  // namespace cgrouprc
 }  // namespace android
@@ -296,10 +307,11 @@ bool CgroupSetup() {
     }
 
     // setup cgroups
-    for (const auto& [name, descriptor] : descriptors) {
-        if (!SetupCgroup(descriptor)) {
+    for (auto& [name, descriptor] : descriptors) {
+        if (SetupCgroup(descriptor)) {
+            descriptor.set_mounted(true);
+        } else {
             // issue a warning and proceed with the next cgroup
-            // TODO: mark the descriptor as invalid and skip it in WriteRcFile()
             LOG(WARNING) << "Failed to setup " << name << " cgroup";
         }
     }