From cee468fb793891fafd40bddc41384a229c2d6c57 Mon Sep 17 00:00:00 2001
From: Suren Baghdasaryan <surenb@google.com>
Date: Thu, 23 Jan 2020 16:18:13 -0800
Subject: [PATCH] Revive ACgroupController_getFlags LLNDK function to detect
 missing cgroups

ACgroupController_getFlags was reverted due to LLNDK breakage, however
it allows detection of cgroups that failed to mount in a more efficient
way. Revive the function as a weakly linked symbol to allow for it to
be missing in case older LLNDK library is being used with the new
system software. This effectively reverts the commit
aa1d54f0ccbb "Remove ACgroupController_getFlags to fix API breakage"'
except it declares ACgroupController_getFlags function as weak and
targets it for API level 30. If LLNKD library does not contain
ACgroupController_getFlags the behavior falls back to the current
way of identifying cgroups that failed to mount.

Test: build and verify correct operation with a missing cgroup
Change-Id: I9158ef53aba97972d41d71dd3396ac43796a7004
Merged-In: I9158ef53aba97972d41d71dd3396ac43796a7004
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 libprocessgroup/cgroup_map.cpp                | 20 +++++++++++++++----
 .../cgrouprc/cgroup_controller.cpp            |  5 +++++
 .../cgrouprc/include/android/cgrouprc.h       | 13 +++++++++++-
 .../cgrouprc/libcgrouprc.llndk.txt            |  7 +++++++
 4 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/libprocessgroup/cgroup_map.cpp b/libprocessgroup/cgroup_map.cpp
index 20ae2be77..2fc920b54 100644
--- a/libprocessgroup/cgroup_map.cpp
+++ b/libprocessgroup/cgroup_map.cpp
@@ -71,7 +71,12 @@ bool CgroupController::IsUsable() {
     if (!HasValue()) return false;
 
     if (state_ == UNKNOWN) {
-        state_ = access(GetProcsFilePath("", 0, 0).c_str(), F_OK) == 0 ? USABLE : MISSING;
+        if (ACgroupController_getFlags != nullptr) {
+            uint32_t flags = ACgroupController_getFlags(controller_);
+            state_ = (flags & CGROUPRC_CONTROLLER_FLAG_MOUNTED) != 0 ? USABLE : MISSING;
+        } else {
+            state_ = access(GetProcsFilePath("", 0, 0).c_str(), F_OK) == 0 ? USABLE : MISSING;
+        }
     }
 
     return state_ == USABLE;
@@ -161,9 +166,16 @@ void CgroupMap::Print() const {
     auto controller_count = ACgroupFile_getControllerCount();
     for (uint32_t i = 0; i < controller_count; ++i) {
         const ACgroupController* controller = ACgroupFile_getController(i);
-        LOG(INFO) << "\t" << ACgroupController_getName(controller) << " ver "
-                  << ACgroupController_getVersion(controller) << " path "
-                  << ACgroupController_getPath(controller);
+        if (ACgroupController_getFlags != nullptr) {
+            LOG(INFO) << "\t" << ACgroupController_getName(controller) << " ver "
+                      << ACgroupController_getVersion(controller) << " path "
+                      << ACgroupController_getPath(controller) << " flags "
+                      << ACgroupController_getFlags(controller);
+        } else {
+            LOG(INFO) << "\t" << ACgroupController_getName(controller) << " ver "
+                      << ACgroupController_getVersion(controller) << " path "
+                      << ACgroupController_getPath(controller);
+        }
     }
 }
 
diff --git a/libprocessgroup/cgrouprc/cgroup_controller.cpp b/libprocessgroup/cgrouprc/cgroup_controller.cpp
index d064d312e..5a326e55d 100644
--- a/libprocessgroup/cgrouprc/cgroup_controller.cpp
+++ b/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();
diff --git a/libprocessgroup/cgrouprc/include/android/cgrouprc.h b/libprocessgroup/cgrouprc/include/android/cgrouprc.h
index 0f6a9cd5d..0ce51237a 100644
--- a/libprocessgroup/cgrouprc/include/android/cgrouprc.h
+++ b/libprocessgroup/cgrouprc/include/android/cgrouprc.h
@@ -66,10 +66,21 @@ __attribute__((warn_unused_result)) uint32_t ACgroupController_getVersion(const
         __INTRODUCED_IN(29);
 
 /**
- * Flag bitmask to be used when ACgroupController_getFlags can be exported
+ * Flag bitmask used in ACgroupController_getFlags
  */
 #define CGROUPRC_CONTROLLER_FLAG_MOUNTED 0x1
 
+#if __ANDROID_API__ >= __ANDROID_API_R__
+
+/**
+ * Returns the flags bitmask of the given controller.
+ * If the given controller is null, return 0.
+ */
+__attribute__((warn_unused_result, weak)) uint32_t ACgroupController_getFlags(
+        const ACgroupController*) __INTRODUCED_IN(30);
+
+#endif
+
 /**
  * Returns the name of the given controller.
  * If the given controller is null, return nullptr.
diff --git a/libprocessgroup/cgrouprc/libcgrouprc.llndk.txt b/libprocessgroup/cgrouprc/libcgrouprc.llndk.txt
index 91df3929d..ce5c419a3 100644
--- a/libprocessgroup/cgrouprc/libcgrouprc.llndk.txt
+++ b/libprocessgroup/cgrouprc/libcgrouprc.llndk.txt
@@ -9,3 +9,10 @@ LIBCGROUPRC { # introduced=29
   local:
     *;
 };
+
+LIBCGROUPRC_30 { # introduced=30
+  global:
+    ACgroupController_getFlags;
+  local:
+    *;
+};