Non-SFI NaCl: Batch-open resource files

components/nacl/loader/nonsfi/irt_resource_open.cc

 // Copyright 2014 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 <pthread.h>
+
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
 #include "components/nacl/loader/nonsfi/irt_interfaces.h"
 #include "ppapi/nacl_irt/irt_manifest.h"
 
 namespace nacl {
 namespace nonsfi {
 
+namespace {
+
+pthread_mutex_t g_mu = PTHREAD_MUTEX_INITIALIZER;
+std::map<std::string, int>* g_fds;
+
+}  // namespace
+
+void RegisterPreopenedDescriptors(
+    const std::vector<std::pair<std::string, int> >& key_fd_pairs) {
+  pthread_mutex_lock(&g_mu);
+  g_fds = new std::map<std::string, int>;
+  for (size_t i = 0; i < key_fd_pairs.size(); ++i)
+    g_fds->insert(key_fd_pairs[i]);
+  pthread_mutex_unlock(&g_mu);
+}
+
+int IrtOpenResource(const char* file, int* fd) {
+  pthread_mutex_lock(&g_mu);
+  if (g_fds) {
+    std::map<std::string, int>::iterator it;
+    if (file[0] == '/')
+      it = g_fds->find(file + 1);
+    else
+      it = g_fds->find(file);
+    if (it != g_fds->end()) {
+      *fd = it->second;
+      g_fds->erase(it);

[teravest, 2014/11/10 20:36:12]

Are the preopened resources only ever opened once with open_resource()? I
suppose this is reasonable, but this is a little surprising; I had expected the
returned fd to come from a dup() call.

[Yusuke Sato, 2014/11/11 00:58:35]

I think this is reasonable.

* The dynamic linker (runnable-ld) opens each DT_NEEDED DSO only once.
* A NaCl app may call dlopen and dlclose like this:

 libX_handle = dlopen("libX.so");
 dlclose(libX_so_handle);
 libX_handle = dlopen("libX.so");
 dlclose(libX_so_handle);

but nacl_io (or an equivalent library) can be implemented in a way that dlclose
does not actually close a FD for libX.so with __nacl_irt_close() but instead
reuse the dlclose'ed FD. Our nacl_io-like library for ARC already does that.

* If a NaCl app does this:

 libX_handle = dlopen("libX.so");
 libX_handle2 = dlopen("libX.so");
 dlclose(libX_so_handle);
 dlclose(libX_so_handle2);

the second dlopen() ends up sending a open_resource IPC to the renderer which is
slow, but no application I know does this.

+      pthread_mutex_unlock(&g_mu);
+      return 0;
+    }
+  }
+  pthread_mutex_unlock(&g_mu);
+  return ppapi::IrtOpenResource(file, fd);
+}
+
 const nacl_irt_resource_open kIrtResourceOpen = {
-  ppapi::IrtOpenResource,
+  nacl::nonsfi::IrtOpenResource,
 };
 
 }  // namespace nonsfi
 }  // namespace nacl