Create a timerfd JNI class

The timerfd delivers timer expiration notifications via a file
descriptor, which can be used to implement delayed callbacks.
Create a JNI class to interface with the timerfd system calls.

Bug: 366373064
Test: m
Change-Id: I0ae7a4cf618838e614b2fa4523b55a4d0e8f74e2

service/Android.bp

@@ -90,6 +90,7 @@ cc_library_shared {
     static_libs: [
         "libnet_utils_device_common_bpfjni",
         "libnet_utils_device_common_bpfutils",
+        "libnet_utils_device_common_timerfdjni",
     ],
     shared_libs: [
         "liblog",

staticlibs/native/timerfdutils/Android.bp

@@ -0,0 +1,46 @@
+// Copyright (C) 2024 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package {
+    default_team: "trendy_team_fwk_core_networking",
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+cc_library_static {
+    name: "libnet_utils_device_common_timerfdjni",
+    srcs: [
+        "com_android_net_module_util_TimerFdUtils.cpp",
+    ],
+    header_libs: [
+        "jni_headers",
+    ],
+    shared_libs: [
+        "liblog",
+        "libnativehelper_compat_libc++",
+    ],
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-parameter",
+    ],
+    sdk_version: "current",
+    min_sdk_version: "30",
+    apex_available: [
+        "com.android.tethering",
+        "//apex_available:platform",
+    ],
+    visibility: [
+        "//packages/modules/Connectivity:__subpackages__",
+    ],
+}

staticlibs/native/timerfdutils/com_android_net_module_util_TimerFdUtils.cpp

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <errno.h>
+#include <jni.h>
+#include <nativehelper/JNIHelp.h>
+#include <nativehelper/scoped_utf_chars.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <sys/timerfd.h>
+#include <time.h>
+#include <unistd.h>
+
+#define MSEC_PER_SEC 1000
+#define NSEC_PER_MSEC 1000000
+
+namespace android {
+
+static jint
+com_android_net_module_util_TimerFdUtils_createTimerFd(JNIEnv *env,
+                                                       jclass clazz) {
+  int tfd;
+  tfd = timerfd_create(CLOCK_BOOTTIME, 0);
+  if (tfd == -1) {
+    jniThrowErrnoException(env, "createTimerFd", tfd);
+  }
+  return tfd;
+}
+
+static void
+com_android_net_module_util_TimerFdUtils_setTime(JNIEnv *env, jclass clazz,
+                                                 jint tfd, jlong milliseconds) {
+  struct itimerspec new_value;
+  new_value.it_value.tv_sec = milliseconds / MSEC_PER_SEC;
+  new_value.it_value.tv_nsec = (milliseconds % MSEC_PER_SEC) * NSEC_PER_MSEC;
+  // Set the interval time to 0 because it's designed for repeated timer expirations after the
+  // initial expiration, which doesn't fit the current usage.
+  new_value.it_interval.tv_sec = 0;
+  new_value.it_interval.tv_nsec = 0;
+
+  int ret = timerfd_settime(tfd, 0, &new_value, NULL);
+  if (ret == -1) {
+    jniThrowErrnoException(env, "setTime", ret);
+  }
+}
+
+/*
+ * JNI registration.
+ */
+static const JNINativeMethod gMethods[] = {
+    /* name, signature, funcPtr */
+    {"createTimerFd", "()I",
+     (void *)com_android_net_module_util_TimerFdUtils_createTimerFd},
+    {"setTime", "(IJ)V",
+     (void *)com_android_net_module_util_TimerFdUtils_setTime},
+};
+
+int register_com_android_net_module_util_TimerFdUtils(JNIEnv *env,
+                                                      char const *class_name) {
+  return jniRegisterNativeMethods(env, class_name, gMethods, NELEM(gMethods));
+}
+
+}; // namespace android

tests/unit/jni/Android.bp

@@ -42,6 +42,7 @@ cc_library_shared {
     ],
     static_libs: [
         "libnet_utils_device_common_bpfjni",
+        "libnet_utils_device_common_timerfdjni",
         "libtcutils",
     ],
     shared_libs: [