Extract CreateInitProcessReaper() from the Zygote.

sandbox/linux/services/init_process_reaper.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/services/init_process_reaper.h"
+
+#include <signal.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "base/callback.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+
+namespace sandbox {
+
+namespace {
+
+void DoNothingSignalHandler(int signal) {
+}
+
+}  // namespace
+
+bool CreateInitProcessReaper(base::Closure* post_fork_parent_callback) {
+  int sync_fds[2];
+  // We want to use send, so we can't use a pipe
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, sync_fds)) {
+    LOG(ERROR) << "Failed to create socketpair";
+    return false;
+  }
+  // We use normal fork, not the ForkDelegate in this case since we are not a
+  // true Zygote yet.
+  pid_t child_pid = fork();
+  if (child_pid == -1) {
+    (void) HANDLE_EINTR(close(sync_fds[0]));
+    (void) HANDLE_EINTR(close(sync_fds[1]));
+    return false;
+  }
+  if (child_pid) {
+    // We are the parent, assuming the role of an init process.
+    // The disposition for SIGCHLD cannot be SIG_IGN or wait() will only return
+    // once all of our childs are dead. Since we're init we need to reap childs
+    // as they come.
+    struct sigaction action;
+    memset(&action, 0, sizeof(action));
+    action.sa_handler = &DoNothingSignalHandler;
+    CHECK(sigaction(SIGCHLD, &action, NULL) == 0);
+
+    (void) HANDLE_EINTR(close(sync_fds[0]));
+    shutdown(sync_fds[1], SHUT_RD);
+    if (post_fork_parent_callback)
+      post_fork_parent_callback->Run();
+    // Tell the child to continue
+    CHECK(HANDLE_EINTR(send(sync_fds[1], "C", 1, MSG_NOSIGNAL)) == 1);
+    (void) HANDLE_EINTR(close(sync_fds[1]));
+
+    for (;;) {
+      // Loop until we have reaped our one natural child
+      siginfo_t reaped_child_info;
+      int wait_ret =
+        HANDLE_EINTR(waitid(P_ALL, 0, &reaped_child_info, WEXITED));
+      if (wait_ret)
+        _exit(1);
+      if (reaped_child_info.si_pid == child_pid) {
+        int exit_code = 0;
+        // We're done waiting
+        if (reaped_child_info.si_code == CLD_EXITED) {
+          exit_code = reaped_child_info.si_status;
+        }
+        // Exit with the same exit code as our parent. This is most likely
+        // useless. _exit with 0 if we got signaled.
+        _exit(exit_code);
+      }
+    }
+  } else {
+    // The child needs to wait for the parent to close kZygoteIdFd to avoid a
+    // race condition
+    (void) HANDLE_EINTR(close(sync_fds[1]));
+    shutdown(sync_fds[0], SHUT_WR);
+    char should_continue;
+    int read_ret = HANDLE_EINTR(read(sync_fds[0], &should_continue, 1));
+    (void) HANDLE_EINTR(close(sync_fds[0]));
+    if (read_ret == 1)
+      return true;
+    else
+      return false;
+  }
+}
+
+}  // namespace sandbox.