1// Copyright 2014 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#ifndef BASE_MAC_SCOPED_MACH_VM_H_
6#define BASE_MAC_SCOPED_MACH_VM_H_
7
8#include <mach/mach.h>
9
10#include <algorithm>
11
12#include "base/base_export.h"
13#include "base/basictypes.h"
14#include "base/logging.h"
15
16// Use ScopedMachVM to supervise ownership of pages in the current process
17// through the Mach VM subsystem. Pages allocated with vm_allocate can be
18// released when exiting a scope with ScopedMachVM.
19//
20// The Mach VM subsystem operates on a page-by-page basis, and a single VM
21// allocation managed by a ScopedMachVM object may span multiple pages. As far
22// as Mach is concerned, allocated pages may be deallocated individually. This
23// is in contrast to higher-level allocators such as malloc, where the base
24// address of an allocation implies the size of an allocated block.
25// Consequently, it is not sufficient to just pass the base address of an
26// allocation to ScopedMachVM, it also needs to know the size of the
27// allocation. To avoid any confusion, both the base address and size must
28// be page-aligned.
29//
30// When dealing with Mach VM, base addresses will naturally be page-aligned,
31// but user-specified sizes may not be. If there's a concern that a size is
32// not page-aligned, use the mach_vm_round_page macro to correct it.
33//
34// Example:
35//
36//   vm_address_t address = 0;
37//   vm_size_t size = 12345;  // This requested size is not page-aligned.
38//   kern_return_t kr =
39//       vm_allocate(mach_task_self(), &address, size, VM_FLAGS_ANYWHERE);
40//   if (kr != KERN_SUCCESS) {
41//     return false;
42//   }
43//   ScopedMachVM vm_owner(address, mach_vm_round_page(size));
44
45namespace base {
46namespace mac {
47
48class BASE_EXPORT ScopedMachVM {
49 public:
50  explicit ScopedMachVM(vm_address_t address = 0, vm_size_t size = 0)
51      : address_(address),
52        size_(size) {
53    DCHECK(address % PAGE_SIZE == 0);
54    DCHECK(size % PAGE_SIZE == 0);
55  }
56
57  ~ScopedMachVM() {
58    if (size_) {
59      vm_deallocate(mach_task_self(), address_, size_);
60    }
61  }
62
63  void reset(vm_address_t address = 0, vm_size_t size = 0);
64
65  vm_address_t address() const {
66    return address_;
67  }
68
69  vm_size_t size() const {
70    return size_;
71  }
72
73  void swap(ScopedMachVM& that) {
74    std::swap(address_, that.address_);
75    std::swap(size_, that.size_);
76  }
77
78  void release() {
79    address_ = 0;
80    size_ = 0;
81  }
82
83 private:
84  vm_address_t address_;
85  vm_size_t size_;
86
87  DISALLOW_COPY_AND_ASSIGN(ScopedMachVM);
88};
89
90}  // namespace mac
91}  // namespace base
92
93#endif  // BASE_MAC_SCOPED_MACH_VM_H_
94