init: Introduce class InterprocessFifo

Prepare for introducing a second interprocess communication channel by
introducing the class InterprocessFifo. Stop using std::unique_ptr<> for
holding the pipe file descriptors. Handle EOF consistently.

Bug: 213617178
Change-Id: Ic0cf18d3d8ea61b8ee17e64de8a9df2736e26728
Signed-off-by: Bart Van Assche <bvanassche@google.com>

init/Android.bp

@@ -39,6 +39,7 @@ init_common_sources = [
     "epoll.cpp",
     "import_parser.cpp",
     "interface_utils.cpp",
+    "interprocess_fifo.cpp",
     "keychords.cpp",
     "parser.cpp",
     "property_type.cpp",
@@ -467,6 +468,7 @@ cc_test {
         "epoll_test.cpp",
         "firmware_handler_test.cpp",
         "init_test.cpp",
+        "interprocess_fifo_test.cpp",
         "keychords_test.cpp",
         "oneshot_on_test.cpp",
         "persistent_properties_test.cpp",
@@ -481,7 +483,10 @@ cc_test {
         "ueventd_test.cpp",
         "util_test.cpp",
     ],
-    static_libs: ["libinit"],
+    static_libs: [
+        "libgmock",
+        "libinit",
+    ],
 
     test_suites: [
         "cts",

init/interprocess_fifo.cpp

@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2022 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 "interprocess_fifo.h"
+
+#include <android-base/logging.h>
+
+#include <unistd.h>
+
+using ::android::base::ErrnoError;
+using ::android::base::Error;
+using ::android::base::Result;
+
+namespace android {
+namespace init {
+
+InterprocessFifo::InterprocessFifo() noexcept : fds_({-1, -1}) {}
+
+InterprocessFifo::InterprocessFifo(InterprocessFifo&& orig) noexcept : fds_({-1, -1}) {
+    std::swap(fds_, orig.fds_);
+}
+
+InterprocessFifo::~InterprocessFifo() noexcept {
+    Close();
+}
+
+void InterprocessFifo::CloseFd(int& fd) noexcept {
+    if (fd >= 0) {
+        close(fd);
+        fd = -1;
+    }
+}
+
+void InterprocessFifo::CloseReadFd() noexcept {
+    CloseFd(fds_[0]);
+}
+
+void InterprocessFifo::CloseWriteFd() noexcept {
+    CloseFd(fds_[1]);
+}
+
+void InterprocessFifo::Close() noexcept {
+    CloseReadFd();
+    CloseWriteFd();
+}
+
+Result<void> InterprocessFifo::Initialize() noexcept {
+    if (fds_[0] >= 0) {
+        return Error() << "already initialized";
+    }
+    if (pipe(fds_.data()) < 0) {  // NOLINT(android-cloexec-pipe)
+        return ErrnoError() << "pipe()";
+    }
+    return {};
+}
+
+Result<uint8_t> InterprocessFifo::Read() noexcept {
+    uint8_t byte;
+    ssize_t count = read(fds_[0], &byte, 1);
+    if (count < 0) {
+        return ErrnoError() << "read()";
+    }
+    if (count == 0) {
+        return Error() << "read() EOF";
+    }
+    DCHECK_EQ(count, 1);
+    return byte;
+}
+
+Result<void> InterprocessFifo::Write(uint8_t byte) noexcept {
+    ssize_t written = write(fds_[1], &byte, 1);
+    if (written < 0) {
+        return ErrnoError() << "write()";
+    }
+    if (written == 0) {
+        return Error() << "write() EOF";
+    }
+    DCHECK_EQ(written, 1);
+    return {};
+}
+
+}  // namespace init
+}  // namespace android

init/interprocess_fifo.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2022 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.
+ */
+
+#pragma once
+
+#include <array>
+
+#include <android-base/result.h>
+
+namespace android {
+namespace init {
+
+// A FIFO for inter-process communication that uses a Unix pipe internally.
+class InterprocessFifo {
+  public:
+    template <typename T>
+    using Result = ::android::base::Result<T>;
+
+    InterprocessFifo() noexcept;
+    InterprocessFifo(const InterprocessFifo& orig) noexcept = delete;
+    InterprocessFifo(InterprocessFifo&& orig) noexcept;
+    InterprocessFifo& operator=(const InterprocessFifo& orig) noexcept = delete;
+    InterprocessFifo& operator=(InterprocessFifo&& orig) noexcept = delete;
+    ~InterprocessFifo() noexcept;
+    void CloseReadFd() noexcept;
+    void CloseWriteFd() noexcept;
+    void Close() noexcept;
+    Result<void> Initialize() noexcept;
+    Result<void> Write(uint8_t byte) noexcept;
+    Result<uint8_t> Read() noexcept;
+
+  private:
+    static void CloseFd(int& fd) noexcept;
+
+    std::array<int, 2> fds_;
+};
+
+}  // namespace init
+}  // namespace android

init/interprocess_fifo_test.cpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2022 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 "interprocess_fifo.h"
+
+#include <android-base/result-gmock.h>
+#include <gtest/gtest.h>
+
+#define ASSERT_OK(e) ASSERT_THAT(e, Ok())
+#define ASSERT_NOT_OK(e) ASSERT_THAT(e, Not(Ok()))
+
+using ::android::base::Result;
+using ::android::base::testing::Ok;
+using ::testing::Not;
+
+namespace android {
+namespace init {
+
+TEST(FifoTest, WriteAndRead) {
+    InterprocessFifo fifo;
+    ASSERT_OK(fifo.Initialize());
+    ASSERT_OK(fifo.Write('a'));
+    ASSERT_OK(fifo.Write('b'));
+    Result<uint8_t> result = fifo.Read();
+    ASSERT_OK(result);
+    EXPECT_EQ(*result, 'a');
+    result = fifo.Read();
+    ASSERT_OK(result);
+    EXPECT_EQ(*result, 'b');
+    InterprocessFifo fifo2 = std::move(fifo);
+    ASSERT_NOT_OK(fifo.Write('c'));
+    ASSERT_NOT_OK(fifo.Read());
+    ASSERT_OK(fifo2.Write('d'));
+    result = fifo2.Read();
+    ASSERT_OK(result);
+    EXPECT_EQ(*result, 'd');
+}
+
+}  // namespace init
+}  // namespace android

init/service.cpp

@@ -38,6 +38,7 @@
 
 #include <string>
 
+#include "interprocess_fifo.h"
 #include "lmkd_service.h"
 #include "service_list.h"
 #include "util.h"
@@ -442,14 +443,6 @@ Result<void> Service::ExecStart() {
     return {};
 }
 
-static void ClosePipe(const std::array<int, 2>* pipe) {
-    for (const auto fd : *pipe) {
-        if (fd >= 0) {
-            close(fd);
-        }
-    }
-}
-
 Result<void> Service::CheckConsole() {
     if (!(flags_ & SVC_CONSOLE)) {
         return {};
@@ -514,7 +507,7 @@ void Service::ConfigureMemcg() {
 
 // Enters namespaces, sets environment variables, writes PID files and runs the service executable.
 void Service::RunService(const std::vector<Descriptor>& descriptors,
-                         std::unique_ptr<std::array<int, 2>, decltype(&ClosePipe)> pipefd) {
+                         InterprocessFifo cgroups_activated) {
     if (auto result = EnterNamespaces(namespaces_, name_, mount_namespace_); !result.ok()) {
         LOG(FATAL) << "Service '" << name_ << "' failed to set up namespaces: " << result.error();
     }
@@ -536,12 +529,12 @@ void Service::RunService(const std::vector<Descriptor>& descriptors,
 
     // Wait until the cgroups have been created and until the cgroup controllers have been
     // activated.
-    char byte = 0;
-    if (read((*pipefd)[0], &byte, 1) < 0) {
-        PLOG(ERROR) << "failed to read from notification channel";
+    Result<uint8_t> byte = cgroups_activated.Read();
+    if (!byte.ok()) {
+        LOG(ERROR) << name_ << ": failed to read from notification channel: " << byte.error();
     }
-    pipefd.reset();
-    if (!byte) {
+    cgroups_activated.Close();
+    if (!*byte) {
         LOG(FATAL) << "Service '" << name_  << "' failed to start due to a fatal error";
         _exit(EXIT_FAILURE);
     }
@@ -605,10 +598,10 @@ Result<void> Service::Start() {
         return {};
     }
 
-    std::unique_ptr<std::array<int, 2>, decltype(&ClosePipe)> pipefd(new std::array<int, 2>{-1, -1},
-                                                                     ClosePipe);
-    if (pipe(pipefd->data()) < 0) {
-        return ErrnoError() << "pipe()";
+    InterprocessFifo cgroups_activated;
+
+    if (Result<void> result = cgroups_activated.Initialize(); !result.ok()) {
+        return result;
     }
 
     if (Result<void> result = CheckConsole(); !result.ok()) {
@@ -667,8 +660,11 @@ Result<void> Service::Start() {
 
     if (pid == 0) {
         umask(077);
-        RunService(descriptors, std::move(pipefd));
+        cgroups_activated.CloseWriteFd();
+        RunService(descriptors, std::move(cgroups_activated));
         _exit(127);
+    } else {
+        cgroups_activated.CloseReadFd();
     }
 
     if (pid < 0) {
@@ -697,8 +693,9 @@ Result<void> Service::Start() {
                          limit_percent_ != -1 || !limit_property_.empty();
         errno = -createProcessGroup(proc_attr_.uid, pid_, use_memcg);
         if (errno != 0) {
-            if (char byte = 0; write((*pipefd)[1], &byte, 1) < 0) {
-                return ErrnoError() << "sending notification failed";
+            Result<void> result = cgroups_activated.Write(0);
+            if (!result.ok()) {
+                return Error() << "Sending notification failed: " << result.error();
             }
             return Error() << "createProcessGroup(" << proc_attr_.uid << ", " << pid_
                            << ") failed for service '" << name_ << "'";
@@ -720,8 +717,8 @@ Result<void> Service::Start() {
         LmkdRegister(name_, proc_attr_.uid, pid_, oom_score_adjust_);
     }
 
-    if (char byte = 1; write((*pipefd)[1], &byte, 1) < 0) {
-        return ErrnoError() << "sending notification failed";
+    if (Result<void> result = cgroups_activated.Write(1); !result.ok()) {
+        return Error() << "Sending cgroups activated notification failed: " << result.error();
     }
 
     NotifyStateChange("running");

init/service.h

@@ -31,6 +31,7 @@
 
 #include "action.h"
 #include "capabilities.h"
+#include "interprocess_fifo.h"
 #include "keyword_map.h"
 #include "mount_namespace.h"
 #include "parser.h"
@@ -154,9 +155,7 @@ class Service {
     void ResetFlagsForStart();
     Result<void> CheckConsole();
     void ConfigureMemcg();
-    void RunService(
-            const std::vector<Descriptor>& descriptors,
-            std::unique_ptr<std::array<int, 2>, void (*)(const std::array<int, 2>* pipe)> pipefd);
+    void RunService(const std::vector<Descriptor>& descriptors, InterprocessFifo cgroups_activated);
     void SetMountNamespace();
     static unsigned long next_start_order_;
     static bool is_exec_service_running_;