mojo/public/c/system/buffer.h

// Copyright 2014 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.

// This file contains types/constants and functions specific to buffers (and in
// particular shared buffers).
// TODO(vtl): Reorganize this file (etc.) to separate general buffer functions
// from (shared) buffer creation.
//
// Note: This header should be compilable as C.

#ifndef MOJO_PUBLIC_C_SYSTEM_BUFFER_H_
#define MOJO_PUBLIC_C_SYSTEM_BUFFER_H_

#include "mojo/public/c/system/handle.h"
#include "mojo/public/c/system/macros.h"
#include "mojo/public/c/system/result.h"

// |MojoCreateSharedBufferOptions|: Used to specify creation parameters for a
// shared buffer to |MojoCreateSharedBuffer()|.
//   |uint32_t struct_size|: Set to the size of the
//       |MojoCreateSharedBufferOptions| struct. (Used to allow for future
//       extensions.)
//   |MojoCreateSharedBufferOptionsFlags flags|: Reserved for future use.
//       |MOJO_CREATE_SHARED_BUFFER_OPTIONS_FLAG_NONE|: No flags; default mode.
//
// TODO(vtl): Maybe add a flag to indicate whether the memory should be
// executable or not?
// TODO(vtl): Also a flag for discardable (ashmem-style) buffers.

typedef uint32_t MojoCreateSharedBufferOptionsFlags;

#define MOJO_CREATE_SHARED_BUFFER_OPTIONS_FLAG_NONE \
  ((MojoCreateSharedBufferOptionsFlags)0)

MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");
struct MOJO_ALIGNAS(8) MojoCreateSharedBufferOptions {
  uint32_t struct_size;
  MojoCreateSharedBufferOptionsFlags flags;
};
MOJO_STATIC_ASSERT(sizeof(MojoCreateSharedBufferOptions) == 8,
                   "MojoCreateSharedBufferOptions has wrong size");

// |MojoDuplicateBufferHandleOptions|: Used to specify parameters in duplicating
// access to a buffer to |MojoDuplicateBufferHandle()|.
//   |uint32_t struct_size|: Set to the size of the
//       |MojoDuplicateBufferHandleOptions| struct. (Used to allow for future
//       extensions.)
//   |MojoDuplicateBufferHandleOptionsFlags flags|: Reserved for future use.
//       |MOJO_DUPLICATE_BUFFER_HANDLE_OPTIONS_FLAG_NONE|: No flags; default
//       mode.
//
// TODO(vtl): Add flags to remove writability (and executability)? Also, COW?

typedef uint32_t MojoDuplicateBufferHandleOptionsFlags;

#define MOJO_DUPLICATE_BUFFER_HANDLE_OPTIONS_FLAG_NONE \
  ((MojoDuplicateBufferHandleOptionsFlags)0)

struct MOJO_ALIGNAS(8) MojoDuplicateBufferHandleOptions {
  uint32_t struct_size;
  MojoDuplicateBufferHandleOptionsFlags flags;
};
MOJO_STATIC_ASSERT(sizeof(MojoDuplicateBufferHandleOptions) == 8,
                   "MojoDuplicateBufferHandleOptions has wrong size");

// |MojoBufferInformation|: Used to provide information about a buffer (see
// |MojoGetBufferInformation()|.
//   |uint32_t struct_size|: Set to the size of the |MojoBufferInformation|
//       struct. (Used to allow for future extensions.)
//   |MojoBufferInformationFlags flags|: Reserved for future use.
//   |uint64_t num_bytes|: Size of the buffer.
//
// TODO(vtl): Add flags to indicate writability, etc.? Also, type of buffer?

typedef uint32_t MojoBufferInformationFlags;

#define MOJO_BUFFER_INFORMATION_FLAG_NONE ((MojoBufferInformationFlags)0)

struct MOJO_ALIGNAS(8) MojoBufferInformation {
  uint32_t struct_size;
  MojoBufferInformationFlags flags;
  uint64_t num_bytes;
};
MOJO_STATIC_ASSERT(sizeof(MojoBufferInformation) == 16,
                   "MojoBufferInformation has wrong size");

// |MojoMapBufferFlags|: Used to specify different modes to |MojoMapBuffer()|.
//   |MOJO_MAP_BUFFER_FLAG_NONE| - No flags; default mode.

typedef uint32_t MojoMapBufferFlags;

#define MOJO_MAP_BUFFER_FLAG_NONE ((MojoMapBufferFlags)0)

MOJO_BEGIN_EXTERN_C

// |MojoCreateSharedBuffer()|: Creates a buffer of size |num_bytes| bytes that
// can be shared between applications (by duplicating the handle -- see
// |MojoDuplicateBufferHandle()| -- and passing it over a message pipe). To
// access the buffer, one must call |MojoMapBuffer()|.
//
// |options| may be set to null for a shared buffer with the default options.
//
// On success, |*shared_buffer_handle| will be set to the handle for the shared
// buffer. (On failure, it is not modified.) The handle has (at least) the
// following rights: |MOJO_HANDLE_RIGHT_DUPLICATE|,
// |MOJO_HANDLE_RIGHT_TRANSFER|, |MOJO_HANDLE_RIGHT_GET_OPTIONS|,
// |MOJO_HANDLE_RIGHT_SET_OPTIONS|, |MOJO_HANDLE_RIGHT_MAP_READABLE|,
// |MOJO_HANDLE_RIGHT_MAP_WRITABLE|, and |MOJO_HANDLE_RIGHT_MAP_EXECUTABLE|.
//
// Note: While more than |num_bytes| bytes may apparently be
// available/visible/readable/writable, trying to use those extra bytes is
// undefined behavior.
//
// Returns:
//   |MOJO_RESULT_OK| on success.
//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g.,
//       |*options| is invalid).
//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if a process/system/quota/etc. limit has
//       been reached (e.g., if the requested size was too large, or if the
//       maximum number of handles was exceeded).
//   |MOJO_RESULT_UNIMPLEMENTED| if an unsupported flag was set in |*options|.
MojoResult MojoCreateSharedBuffer(
    const struct MojoCreateSharedBufferOptions* MOJO_RESTRICT
        options,                                      // Optional in.
    uint64_t num_bytes,                               // In.
    MojoHandle* MOJO_RESTRICT shared_buffer_handle);  // Out.

// |MojoDuplicateBufferHandle()|: Duplicates the handle |buffer_handle| (which
// must have the |MOJO_HANDLE_RIGHT_DUPLICATE| right) to a buffer. This creates
// another handle (returned in |*new_buffer_handle| on success), which can then
// be sent to another application over a message pipe, while retaining access to
// the |buffer_handle| (and any mappings that it may have).
//
// |options| may be set to null to duplicate the buffer handle with the default
// options.
//
// On success, |*shared_buffer_handle| will be set to the handle for the new
// buffer handle. (On failure, it is not modified.)
//
// Returns:
//   |MOJO_RESULT_OK| on success.
//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g.,
//       |buffer_handle| is not a valid buffer handle or |*options| is invalid).
//   |MOJO_RESULT_PERMISSION_DENIED| if |buffer_handle| does not have the
//       |MOJO_HANDLE_RIGHT_DUPLICATE| right.
//   |MOJO_RESULT_UNIMPLEMENTED| if an unsupported flag was set in |*options|.
//   |MOJO_RESULT_BUSY| if |buffer_handle| is currently in use in some
//       transaction (that, e.g., may result in it being invalidated, such as
//       being sent in a message).
MojoResult MojoDuplicateBufferHandle(
    MojoHandle buffer_handle,  // In.
    const struct MojoDuplicateBufferHandleOptions* MOJO_RESTRICT
        options,                                   // Optional in.
    MojoHandle* MOJO_RESTRICT new_buffer_handle);  // Out.

// |MojoGetBufferInformation()|: Gets information about the buffer with handle
// |buffer_handle| (which must have the |MOJO_HANDLE_RIGHT_GET_OPTIONS| right).
// |info| should be non-null and point to a buffer of size |info_num_bytes|;
// |info_num_bytes| should be at least 16 (the size of the first, and currently
// only, version of |struct MojoBufferInformation|).
//
// On success, |*info| will be filled with information about the given buffer.
// Note that if additional (larger) versions of |struct MojoBufferInformation|
// are defined, the largest version permitted by |info_num_bytes| that is
// supported by the implementation will be filled. Callers expecting more than
// the first 16-byte version must check the resulting |info->struct_size|.
//
// Returns:
//   |MOJO_RESULT_OK| on success.
//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g.,
//       |buffer_handle| is not a valid buffer handle, |*info| is null, or
//       |info_num_bytes| is too small).
//   |MOJO_RESULT_PERMISSION_DENIED| if |buffer_handle| does not have the
//       |MOJO_HANDLE_RIGHT_GET_OPTIONS| right.
//   |MOJO_RESULT_BUSY| if |buffer_handle| is currently in use in some
//       transaction (that, e.g., may result in it being invalidated, such as
//       being sent in a message).
MojoResult MojoGetBufferInformation(MojoHandle buffer_handle,            // In.
                                    struct MojoBufferInformation* info,  // Out.
                                    uint32_t info_num_bytes);            // In.

// |MojoMapBuffer()|: Maps the part (at offset |offset| of length |num_bytes|)
// of the buffer given by |buffer_handle| (which must have both the
// |MOJO_HANDLE_RIGHT_MAP_READABLE| and |MOJO_HANDLE_RIGHT_MAP_WRITABLE| rights)
// into memory, with options specified by |flags|. |offset + num_bytes| must be
// less than or equal to the size of the buffer. On success, |*buffer| points to
// memory with the requested part of the buffer. (On failure, it is not
// modified.)
//
// A single buffer handle may have multiple active mappings (possibly depending
// on the buffer type). The permissions (e.g., writable or executable) of the
// returned memory may depend on the properties of the buffer and properties
// attached to the buffer handle as well as |flags|.
//
// Note: Though data outside the specified range may apparently be
// available/visible/readable/writable, trying to use those extra bytes is
// undefined behavior.
//
// Returns:
//   |MOJO_RESULT_OK| on success.
//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g.,
//       |buffer_handle| is not a valid buffer handle or the range specified by
//       |offset| and |num_bytes| is not valid).
//   |MOJO_RESULT_PERMISSION_DENIED| if |buffer_handle| does not have both the
//       |MOJO_HANDLE_RIGHT_MAP_READABLE| and |MOJO_HANDLE_RIGHT_MAP_WRITABLE|
//       rights.
//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if the mapping operation itself failed
//       (e.g., due to not having appropriate address space available).
//   |MOJO_RESULT_BUSY| if |buffer_handle| is currently in use in some
//       transaction (that, e.g., may result in it being invalidated, such as
//       being sent in a message).
MojoResult MojoMapBuffer(MojoHandle buffer_handle,   // In.
                         uint64_t offset,            // In.
                         uint64_t num_bytes,         // In.
                         void** buffer,              // Out.
                         MojoMapBufferFlags flags);  // In.

// |MojoUnmapBuffer()|: Unmaps a buffer pointer that was mapped by
// |MojoMapBuffer()|. |buffer| must have been the result of |MojoMapBuffer()|
// (not some other pointer inside the mapped memory), and the entire mapping
// will be removed (partial unmapping is not supported). A mapping may only be
// unmapped once.
//
// Returns:
//   |MOJO_RESULT_OK| on success.
//   |MOJO_RESULT_INVALID_ARGUMENT| if |buffer| is invalid (e.g., is not the
//       result of |MojoMapBuffer()| or has already been unmapped).
MojoResult MojoUnmapBuffer(void* buffer);  // In.

MOJO_END_EXTERN_C

#endif  // MOJO_PUBLIC_C_SYSTEM_BUFFER_H_