blob: c7d14833c75adfec935b5a31cd718ac83bbf868b [file] [log] [blame]
// Copyright 2018 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 <utility>
#include "base/macros.h"
#include "base/memory/platform_shared_memory_region.h"
#include "base/memory/shared_memory_mapping.h"
namespace base {
struct MappedReadOnlyRegion;
// Scoped move-only handle to a region of platform shared memory. The instance
// owns the platform handle it wraps. Mappings created by this region are
// read-only. These mappings remain valid even after the region handle is moved
// or destroyed.
class BASE_EXPORT ReadOnlySharedMemoryRegion {
using MappingType = ReadOnlySharedMemoryMapping;
// Creates a new ReadOnlySharedMemoryRegion instance of a given size along
// with the WritableSharedMemoryMapping which provides the only way to modify
// the content of the newly created region. The returned region and mapping
// are guaranteed to either be both valid or both invalid. Use
// |MappedReadOnlyRegion::IsValid()| as a shortcut for checking creation
// success.
// This means that the caller's process is the only process that can modify
// the region content. If you need to pass write access to another process,
// consider using WritableSharedMemoryRegion or UnsafeSharedMemoryRegion.
// This call will fail if the process does not have sufficient permissions to
// create a shared memory region itself. See
// mojo::CreateReadOnlySharedMemoryRegion in
// mojo/public/cpp/base/shared_memory_utils.h for creating a shared memory
// region from a an unprivileged process where a broker must be used.
static MappedReadOnlyRegion Create(size_t size);
// Returns a ReadOnlySharedMemoryRegion built from a platform-specific handle
// that was taken from another ReadOnlySharedMemoryRegion instance. Returns an
// invalid region iff the |handle| is invalid. CHECK-fails if the |handle|
// isn't read-only.
// This should be used only by the code passing handles across process
// boundaries.
static ReadOnlySharedMemoryRegion Deserialize(
subtle::PlatformSharedMemoryRegion handle);
// Extracts a platform handle from the region. Ownership is transferred to the
// returned region object.
// This should be used only for sending the handle from the current process to
// another.
static subtle::PlatformSharedMemoryRegion TakeHandleForSerialization(
ReadOnlySharedMemoryRegion region);
// Default constructor initializes an invalid instance.
// Move operations are allowed.
ReadOnlySharedMemoryRegion& operator=(ReadOnlySharedMemoryRegion&&);
// Destructor closes shared memory region if valid.
// All created mappings will remain valid.
// Duplicates the underlying platform handle and creates a new
// ReadOnlySharedMemoryRegion instance that owns this handle. Returns a valid
// ReadOnlySharedMemoryRegion on success, invalid otherwise. The current
// region instance remains valid in any case.
ReadOnlySharedMemoryRegion Duplicate() const;
// Maps the shared memory region into the caller's address space with
// read-only access. The mapped address is guaranteed to have an alignment of
// at least |subtle::PlatformSharedMemoryRegion::kMapMinimumAlignment|.
// Returns a valid ReadOnlySharedMemoryMapping instance on success, invalid
// otherwise.
ReadOnlySharedMemoryMapping Map() const;
// Same as above, but maps only |size| bytes of the shared memory region
// starting with the given |offset|. |offset| must be aligned to value of
// |SysInfo::VMAllocationGranularity()|. Returns an invalid mapping if
// requested bytes are out of the region limits.
ReadOnlySharedMemoryMapping MapAt(off_t offset, size_t size) const;
// Whether the underlying platform handle is valid.
bool IsValid() const;
// Returns the maximum mapping size that can be created from this region.
size_t GetSize() const {
return handle_.GetSize();
// Returns 128-bit GUID of the region.
const UnguessableToken& GetGUID() const {
return handle_.GetGUID();
explicit ReadOnlySharedMemoryRegion(
subtle::PlatformSharedMemoryRegion handle);
subtle::PlatformSharedMemoryRegion handle_;
// Helper struct for return value of ReadOnlySharedMemoryRegion::Create().
struct MappedReadOnlyRegion {
ReadOnlySharedMemoryRegion region;
WritableSharedMemoryMapping mapping;
// Helper function to check return value of
// ReadOnlySharedMemoryRegion::Create(). |region| and |mapping| either both
// valid or invalid.
bool IsValid() {
DCHECK_EQ(region.IsValid(), mapping.IsValid());
return region.IsValid() && mapping.IsValid();
} // namespace base