Implement SharedMemory::NewAnonymousReadOnly(contents).

base/memory/shared_memory_posix.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 "base/memory/shared_memory.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ skipping 83 matching lines @@
   DCHECK_GE(handle.fd, 0);
   if (HANDLE_EINTR(close(handle.fd)) < 0)
     DPLOG(ERROR) << "close";
 }
 
 // static
 size_t SharedMemory::GetHandleLimit() {
   return base::GetMaxFds();
 }
 
+// static
+scoped_ptr<SharedMemory> SharedMemory::NewAnonymousReadOnly(
+    StringPiece contents) {
+  // This function theoretically can block on the disk, but realistically
+  // the temporary files we create will just go into the buffer cache
+  // and be deleted before they ever make it out to disk.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
+  FilePath path;
+  file_util::ScopedFILE writable_fp(
+      file_util::CreateAndOpenTemporaryShmemFile(&path, /*executable=*/false));
+  if (!writable_fp) {
+    LOG(ERROR) << "Failed to create temp shmem file.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  int readonly_fd = HANDLE_EINTR(open(path.value().c_str(), O_RDONLY));
+  if (readonly_fd < 0) {
+    PLOG(ERROR) << "Failed to reopen temp shmem file readonly.";
+    return scoped_ptr<SharedMemory>();
+  }
+  file_util::ScopedFD readonly_fd_closer(&readonly_fd);
+
+  if (unlink(path.value().c_str()))
+    PLOG(WARNING) << "unlink";
+
+  if (fwrite(contents.data(), 1, contents.size(), writable_fp.get()) !=
+      contents.size()) {
+    LOG(ERROR) << "Failed to write " << contents.size()
+               << " bytes to memory block.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  if (fclose(writable_fp.release()) != 0) {
+    PLOG(ERROR) << "Failed to flush contents of memory block.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  // Protect against people accidentally reopening as read/write.  It's still
+  // possible to intentionally fchmod() the FD back and then open it from /dev,
+  // but the renderer can't open from a filesystem path.
+  if (0 != fchmod(readonly_fd, S_IRUSR))
+    PLOG(DFATAL) << "Failed to make FD " << readonly_fd << " read-only";
+
+  return make_scoped_ptr(new SharedMemory(
+      FileDescriptor(*readonly_fd_closer.release(), /*iauto_close=*/false),
+      /*read_only=*/true));
+}
+
 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
   return CreateAnonymous(size) && Map(size);
 }
 
 #if !defined(OS_ANDROID)
 // Chromium mostly only uses the unique/private shmem as specified by
 // "name == L"". The exception is in the StatsTable.
 // TODO(jrg): there is no way to "clean up" all unused named shmem if
 // we restart from a crash.  (That isn't a new problem, but it is a problem.)
 // In case we want to delete it later, it may be useful to save the value
@@ skipping 296 matching lines @@
   new_handle->fd = new_fd;
   new_handle->auto_close = true;
 
   if (close_self)
     Close();
 
   return true;
 }
 
 }  // namespace base