base/memory/shared_memory_android.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/memory/shared_memory.h"
   6
   7 #include <sys/mman.h>
   8
   9 #include "base/logging.h"
  10 #include "third_party/ashmem/ashmem.h"
  11
  12 namespace base {
  13
  14 // For Android, we use ashmem to implement SharedMemory. ashmem_create_region
  15 // will automatically pin the region. We never explicitly call pin/unpin. When
  16 // all the file descriptors from different processes associated with the region
  17 // are closed, the memory buffer will go away.
  18
  19 bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
  20   DCHECK_EQ(-1, mapped_file_ );
  21
  22   if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
  23     return false;
  24
  25   // "name" is just a label in ashmem. It is visible in /proc/pid/maps.
  26   mapped_file_ = ashmem_create_region(
  27       options.name == NULL ? "" : options.name->c_str(),
  28       options.size);
  29   if (-1 == mapped_file_) {
  30     DLOG(ERROR) << "Shared memory creation failed";
  31     return false;
  32   }
  33
  34   int err = ashmem_set_prot_region(mapped_file_,
  35                                    PROT_READ | PROT_WRITE | PROT_EXEC);
  36   if (err < 0) {
  37     DLOG(ERROR) << "Error " << err << " when setting protection of ashmem";
  38     return false;
  39   }
  40
  41   // Android doesn't appear to have a way to drop write access on an ashmem
  42   // segment for a single descriptor.  http://crbug.com/320865
  43   readonly_mapped_file_ = dup(mapped_file_);
  44   if (-1 == readonly_mapped_file_) {
  45     DPLOG(ERROR) << "dup() failed";
  46     return false;
  47   }
  48
  49   requested_size_ = options.size;
  50
  51   return true;
  52 }
  53
  54 bool SharedMemory::Delete(const std::string& name) {
  55   // Like on Windows, this is intentionally returning true as ashmem will
  56   // automatically releases the resource when all FDs on it are closed.
  57   return true;
  58 }
  59
  60 bool SharedMemory::Open(const std::string& name, bool read_only) {
  61   // ashmem doesn't support name mapping
  62   NOTIMPLEMENTED();
  63   return false;
  64 }
  65
  66 }  // namespace base