Increase MessageAttachmentSet::kMaxDescriptorsPerMessage

ipc/ipc_channel_nacl.cc

 // Copyright (c) 2012 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 "ipc/ipc_channel_nacl.h"
 
 #include <errno.h>
 #include <stddef.h>
 #include <sys/types.h>
 
@@ skipping 19 matching lines @@
 };
 
 namespace {
 
 bool ReadDataOnReaderThread(int pipe, MessageContents* contents) {
   DCHECK(pipe >= 0);
   if (pipe < 0)
     return false;
 
   contents->data.resize(Channel::kReadBufferSize);
-  contents->fds.resize(MessageAttachmentSet::kMaxDescriptorsPerMessage);
+  contents->fds.resize(NACL_ABI_IMC_DESC_MAX);

[dmichael (off chromium), 2015/03/12 22:07:16]

We want this number to be == kMaxDescriptorsPerMessage, right? Is it possible to
have a static_assert here so we know if one of them changes?

[Yusuke Sato, 2015/03/12 22:19:28]

NACL_ABI_IMC_DESC_MAX defined in native_client/ is currently very small (8,
IIRC) and I think that's okay.

My understanding is that NACL_ABI_IPC_DESC_MAX defines the maximum number of FDs
that can be passed with one message from trusted to untrusted. Since there is no
IRT at this point that requires the trusted side to pass a large number of FDs
at once, I think keeping NACL_ABI_IMC_DESC_MAX small makes sense.

 
   NaClAbiNaClImcMsgIoVec iov = { &contents->data[0], contents->data.size() };
   NaClAbiNaClImcMsgHdr msg = {
     &iov, 1, &contents->fds[0], contents->fds.size()

[Yusuke Sato, 2015/03/12 22:19:28]

.. and if we use 128 (MessageAttachmentSet::kMaxDescriptorsPerMessage) here,
code in native_client/ fails saying that the size is too large.

   };
 
   int bytes_read = imc_recvmsg(pipe, &msg, 0);
 
   if (bytes_read <= 0) {
     // NaClIPCAdapter::BlockingReceive returns -1 when the pipe closes (either
     // due to error or for regular shutdown).
     contents->data.clear();
     contents->fds.clear();
     return false;
@@ skipping 317 matching lines @@
 // Channel's methods
 
 // static
 scoped_ptr<Channel> Channel::Create(
     const IPC::ChannelHandle &channel_handle, Mode mode, Listener* listener) {
   return scoped_ptr<Channel>(
       new ChannelNacl(channel_handle, mode, listener));
 }
 
 }  // namespace IPC