text: // 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 <mach/mach_vm.h>
  #include <stddef.h>
  #include <sys/mman.h>
  #include <sys/stat.h>
  #include <unistd.h>
  
  #include "base/logging.h"
  #include "base/mac/foundation_util.h"
  #include "base/mac/mac_util.h"
  #include "base/mac/scoped_mach_vm.h"
  #include "base/memory/shared_memory_helper.h"
  #include "base/memory/shared_memory_tracker.h"
  #include "base/metrics/field_trial.h"
  #include "base/metrics/histogram_macros.h"
  #include "base/posix/safe_strerror.h"
  #include "base/process/process_metrics.h"
  #include "base/scoped_generic.h"
  #include "base/strings/utf_string_conversions.h"
  #include "base/unguessable_token.h"
  #include "build/build_config.h"
  
  #if defined(OS_IOS)
  #error "MacOS only - iOS uses shared_memory_posix.cc"
  #endif
  
  namespace base {
  
  namespace {
  
  // Returns whether the operation succeeded.
  // |new_handle| is an output variable, populated on success. The caller takes
  // ownership of the underlying memory object.
  // |handle| is the handle to copy.
  // If |handle| is already mapped, |mapped_addr| is its mapped location.
  // Otherwise, |mapped_addr| should be |nullptr|.
  bool MakeMachSharedMemoryHandleReadOnly(SharedMemoryHandle* new_handle,
                                          SharedMemoryHandle handle,
                                          void* mapped_addr) {
    if (!handle.IsValid())
      return false;
  
    size_t size = handle.GetSize();
  
    // Map if necessary.
    void* temp_addr = mapped_addr;
    base::mac::ScopedMachVM scoper;
    if (!temp_addr) {
      // Intentionally lower current prot and max prot to |VM_PROT_READ|.
      kern_return_t kr = mach_vm_map(
          mach_task_self(), reinterpret_cast<mach_vm_address_t*>(&temp_addr),
          size, 0, VM_FLAGS_ANYWHERE, handle.GetMemoryObject(), 0, FALSE,
          VM_PROT_READ, VM_PROT_READ, VM_INHERIT_NONE);
      if (kr != KERN_SUCCESS)
        return false;
      scoper.reset(reinterpret_cast<vm_address_t>(temp_addr),
                   mach_vm_round_page(size));
    }
  
    // Make new memory object.
    mach_port_t named_right;
    kern_return_t kr = mach_make_memory_entry_64(
        mach_task_self(), reinterpret_cast<memory_object_size_t*>(&size),
        reinterpret_cast<memory_object_offset_t>(temp_addr), VM_PROT_READ,
        &named_right, MACH_PORT_NULL);
    if (kr != KERN_SUCCESS)
      return false;
  
    *new_handle = SharedMemoryHandle(named_right, size, handle.GetGUID());
    return true;
  }
  
  }  // namespace
  
  SharedMemory::SharedMemory() {}
  
  SharedMemory::SharedMemory(const SharedMemoryHandle& handle, bool read_only)
      : shm_(handle), read_only_(read_only) {}
  
  SharedMemory::~SharedMemory() {
    Unmap();
    Close();
  }
  
  // static
  bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
    return handle.IsValid();
  }
  
  // static
  void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
    handle.Close();
  }
  
  // static
  SharedMemoryHandle SharedMemory::DuplicateHandle(
      const SharedMemoryHandle& handle) {
    return handle.Duplicate();
  }
  
  bool SharedMemory::CreateAndMapAnonymous(size_t size) {
    return CreateAnonymous(size) && Map(size);
  }
  
  // Chromium mostly only uses the unique/private shmem as specified by
  // "name == L"". The exception is in the StatsTable.
  bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
    DCHECK(!shm_.IsValid());
    if (options.size == 0)
      return false;
  
    if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
      return false;
  
    shm_ = SharedMemoryHandle(options.size, UnguessableToken::Create());
    requested_size_ = options.size;
    return shm_.IsValid();
  }
  
  bool SharedMemory::MapAt(off_t offset, size_t bytes) {
    if (!shm_.IsValid())
      return false;
    if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
      return false;
    if (memory_)
      return false;
  
    bool success = shm_.MapAt(offset, bytes, &memory_, read_only_);
    if (success) {
      mapped_size_ = bytes;
      DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
                        (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
      mapped_id_ = shm_.GetGUID();
      SharedMemoryTracker::GetInstance()->IncrementMemoryUsage(*this);
    } else {
      memory_ = nullptr;
    }
  
    return success;
  }
  
  bool SharedMemory::Unmap() {
    if (!memory_)
      return false;
  
    SharedMemoryTracker::GetInstance()->DecrementMemoryUsage(*this);
        mach_vm_deallocate(mach_task_self(),
                           reinterpret_cast<mach_vm_address_t>(memory_),
                           mapped_size_);
    memory_ = nullptr;
    mapped_size_ = 0;
    mapped_id_ = UnguessableToken();
    return true;
  }
  
  SharedMemoryHandle SharedMemory::handle() const {
    return shm_;
  }
  
  SharedMemoryHandle SharedMemory::TakeHandle() {
    SharedMemoryHandle dup = DuplicateHandle(handle());
    Unmap();
    Close();
    return dup;
  }
  
  void SharedMemory::Close() {
    shm_.Close();
    shm_ = SharedMemoryHandle();
  }
  
  SharedMemoryHandle SharedMemory::GetReadOnlyHandle() const {
    DCHECK(shm_.IsValid());
    SharedMemoryHandle new_handle;
    bool success = MakeMachSharedMemoryHandleReadOnly(&new_handle, shm_, memory_);
    if (success)
      new_handle.SetOwnershipPassesToIPC(true);
    return new_handle;
  }
  
  }  // namespace base
  