commit 4f88670777e05bf7a774d2ff41ffe437eeace0c2
author Carlos Llamas <cmllamas@google.com> Mon Mar 07 22:07:03 2022 -0800
committer Carlos Llamas <cmllamas@google.com> Wed Mar 09 08:52:25 2022 -0800
tree 4d6e978e66134a90b71bdca01631f48087d08253
parent f81decc8b72d5d8d5ae928d1c5755c898fe87db9

libbinder: detect features supported by the driver

The binder driver exposes the features it supports as individual files
under /dev/binderfs/features/*. This patch adds a method to determine
whether a feature is enabled or not and avoid unnecessary calls to the
driver. In this case, we can skip logging any "oneway spam detection"
failures seen during open_driver() if the ioctl is not supported.

Bug: 191910201
Tested: toggling driver features manually
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: Ie8e7315cc1ba8baa9cb03bab1fb3bd7507765c99

libs/binder/ProcessState.cpp

diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index baa817c..b14a838 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -409,6 +409,28 @@
     return 0;
 }
 
+#define DRIVER_FEATURES_PATH "/dev/binderfs/features/"
+bool ProcessState::isDriverFeatureEnabled(const DriverFeature feature) {
+    static const char* const names[] = {
+        [static_cast<int>(DriverFeature::ONEWAY_SPAM_DETECTION)] =
+            DRIVER_FEATURES_PATH "oneway_spam_detection",
+    };
+    int fd = open(names[static_cast<int>(feature)], O_RDONLY | O_CLOEXEC);
+    char on;
+    if (fd == -1) {
+        ALOGE_IF(errno != ENOENT, "%s: cannot open %s: %s", __func__,
+                 names[static_cast<int>(feature)], strerror(errno));
+        return false;
+    }
+    if (read(fd, &on, sizeof(on)) == -1) {
+        ALOGE("%s: error reading to %s: %s", __func__,
+                 names[static_cast<int>(feature)], strerror(errno));
+        return false;
+    }
+    close(fd);
+    return on == '1';
+}
+
 status_t ProcessState::enableOnewaySpamDetection(bool enable) {
     uint32_t enableDetection = enable ? 1 : 0;
     if (ioctl(mDriverFD, BINDER_ENABLE_ONEWAY_SPAM_DETECTION, &enableDetection) == -1) {
@@ -452,7 +474,9 @@
     uint32_t enable = DEFAULT_ENABLE_ONEWAY_SPAM_DETECTION;
     result = ioctl(fd, BINDER_ENABLE_ONEWAY_SPAM_DETECTION, &enable);
     if (result == -1) {
-        ALOGV("Binder ioctl to enable oneway spam detection failed: %s", strerror(errno));
+        ALOGE_IF(ProcessState::isDriverFeatureEnabled(
+                     ProcessState::DriverFeature::ONEWAY_SPAM_DETECTION),
+                 "Binder ioctl to enable oneway spam detection failed: %s", strerror(errno));
     }
     return fd;
 }

libs/binder/include/binder/ProcessState.h

diff --git a/libs/binder/include/binder/ProcessState.h b/libs/binder/include/binder/ProcessState.h
index cf8d8e4..0deee73 100644
--- a/libs/binder/include/binder/ProcessState.h
+++ b/libs/binder/include/binder/ProcessState.h
@@ -91,6 +91,12 @@
      */
     size_t getThreadPoolMaxThreadCount() const;
 
+    enum class DriverFeature {
+        ONEWAY_SPAM_DETECTION,
+    };
+    // Determine whether a feature is supported by the binder driver.
+    static bool isDriverFeatureEnabled(const DriverFeature feature);
+
 private:
     static sp<ProcessState> init(const char* defaultDriver, bool requireDefault);