Linux: refactor zygote support

http://code.google.com/p/chromium/wiki/LinuxZygote

* Move Chrome specific bits out of base
* Move away from the idea of reserved file descriptors (which don't
  really work with zygotes)
* Load resources before forking renderers (means that we don't need
  communication between the zygote process and the renderers)
* Make sure that gdb works against the browser again
* Make sure that we have different ASLR between the renderers and the
  browser.

http://codereview.chromium.org/119335


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@18109 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 168 insertions, 0 deletions

diff --git a/chrome/browser/zygote_main_linux.cc b/chrome/browser/zygote_main_linux.cc
new file mode 100644
index 0000000..d450c39
--- /dev/null
+++ b/chrome/browser/zygote_main_linux.cc
@@ -0,0 +1,168 @@
+// Copyright (c) 2009 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 <unistd.h>
+#include <sys/epoll.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/signal.h>
+
+#include "base/command_line.h"
+#include "base/eintr_wrapper.h"
+#include "base/global_descriptors_posix.h"
+#include "base/pickle.h"
+#include "base/unix_domain_socket_posix.h"
+
+#include "chrome/browser/zygote_host_linux.h"
+#include "chrome/common/chrome_descriptors.h"
+#include "chrome/common/main_function_params.h"
+#include "chrome/common/process_watcher.h"
+
+// http://code.google.com/p/chromium/wiki/LinuxZygote
+
+// This is the object which implements the zygote. The ZygoteMain function,
+// which is called from ChromeMain, at the the bottom and simple constructs one
+// of these objects and runs it.
+class Zygote {
+ public:
+  bool ProcessRequests() {
+    // A SOCK_SEQPACKET socket is installed in fd 3. We get commands from the
+    // browser on it.
+
+    // We need to accept SIGCHLD, even though our handler is a no-op because
+    // otherwise we cannot wait on children. (According to POSIX 2001.)
+    struct sigaction action;
+    memset(&action, 0, sizeof(action));
+    action.sa_handler = SIGCHLDHandler;
+    CHECK(sigaction(SIGCHLD, &action, NULL) == 0);
+
+    for (;;) {
+      if (HandleRequestFromBrowser(3))
+        return true;
+    }
+  }
+
+ private:
+  // See comment below, where sigaction is called.
+  static void SIGCHLDHandler(int signal) { }
+
+  // ---------------------------------------------------------------------------
+  // Requests from the browser...
+
+  // Read and process a request from the browser. Returns true if we are in a
+  // new process and thus need to unwind back into ChromeMain.
+  bool HandleRequestFromBrowser(int fd) {
+    std::vector<int> fds;
+    static const unsigned kMaxMessageLength = 2048;
+    char buf[kMaxMessageLength];
+    const ssize_t len = base::RecvMsg(fd, buf, sizeof(buf), &fds);
+    if (len == -1) {
+      LOG(WARNING) << "Error reading message from browser: " << errno;
+      return false;
+    }
+
+    if (len == 0) {
+      // EOF from the browser. We should die.
+      _exit(0);
+      return false;
+    }
+
+    Pickle pickle(buf, len);
+    void* iter = NULL;
+
+    int kind;
+    if (!pickle.ReadInt(&iter, &kind))
+      goto error;
+
+    if (kind == ZygoteHost::kCmdFork) {
+      return HandleForkRequest(fd, pickle, iter, fds);
+    } else if (kind == ZygoteHost::kCmdReap) {
+      if (fds.size())
+        goto error;
+      return HandleReapRequest(fd, pickle, iter);
+    }
+
+   error:
+    LOG(WARNING) << "Error parsing message from browser";
+    for (std::vector<int>::const_iterator
+         i = fds.begin(); i != fds.end(); ++i)
+      close(*i);
+    return false;
+  }
+
+  bool HandleReapRequest(int fd, Pickle& pickle, void* iter) {
+    pid_t child;
+
+    if (!pickle.ReadInt(&iter, &child)) {
+      LOG(WARNING) << "Error parsing reap request from browser";
+      return false;
+    }
+
+    ProcessWatcher::EnsureProcessTerminated(child);
+
+    return false;
+  }
+
+  // Handle a 'fork' request from the browser: this means that the browser
+  // wishes to start a new renderer.
+  bool HandleForkRequest(int fd, Pickle& pickle, void* iter,
+                         std::vector<int>& fds) {
+    std::vector<std::string> args;
+    int argc, numfds;
+    base::GlobalDescriptors::Mapping mapping;
+    pid_t child;
+
+    if (!pickle.ReadInt(&iter, &argc))
+      goto error;
+
+    for (int i = 0; i < argc; ++i) {
+      std::string arg;
+      if (!pickle.ReadString(&iter, &arg))
+        goto error;
+      args.push_back(arg);
+    }
+
+    if (!pickle.ReadInt(&iter, &numfds))
+      goto error;
+    if (numfds != static_cast<int>(fds.size()))
+      goto error;
+
+    for (int i = 0; i < numfds; ++i) {
+      base::GlobalDescriptors::Key key;
+      if (!pickle.ReadUInt32(&iter, &key))
+        goto error;
+      mapping.push_back(std::make_pair(key, fds[i]));
+    }
+
+    child = fork();
+
+    if (!child) {
+      close(3);  // our socket from the browser is in fd 3
+      Singleton<base::GlobalDescriptors>()->Reset(mapping);
+      CommandLine::Reset();
+      CommandLine::Init(args);
+      return true;
+    }
+
+    for (std::vector<int>::const_iterator
+         i = fds.begin(); i != fds.end(); ++i)
+      close(*i);
+
+    HANDLE_EINTR(write(fd, &child, sizeof(child)));
+    return false;
+
+   error:
+    LOG(WARNING) << "Error parsing fork request from browser";
+    for (std::vector<int>::const_iterator
+         i = fds.begin(); i != fds.end(); ++i)
+      close(*i);
+    return false;
+  }
+  // ---------------------------------------------------------------------------
+};
+
+bool ZygoteMain(const MainFunctionParams& params) {
+  Zygote zygote;
+  return zygote.ProcessRequests();
+}