0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: DTV.dmx
0003
0004 .. _dmx-mmap:
0005
0006 *****************
0007 Digital TV mmap()
0008 *****************
0009
0010 Name
0011 ====
0012
0013 dmx-mmap - Map device memory into application address space
0014
0015 .. warning:: this API is still experimental
0016
0017 Synopsis
0018 ========
0019
0020 .. code-block:: c
0021
0022 #include <unistd.h>
0023 #include <sys/mman.h>
0024
0025 .. c:function:: void *mmap( void *start, size_t length, int prot, int flags, int fd, off_t offset )
0026
0027 Arguments
0028 =========
0029
0030 ``start``
0031 Map the buffer to this address in the application's address space.
0032 When the ``MAP_FIXED`` flag is specified, ``start`` must be a
0033 multiple of the pagesize and mmap will fail when the specified
0034 address cannot be used. Use of this option is discouraged;
0035 applications should just specify a ``NULL`` pointer here.
0036
0037 ``length``
0038 Length of the memory area to map. This must be a multiple of the
0039 DVB packet length (188, on most drivers).
0040
0041 ``prot``
0042 The ``prot`` argument describes the desired memory protection.
0043 Regardless of the device type and the direction of data exchange it
0044 should be set to ``PROT_READ`` | ``PROT_WRITE``, permitting read
0045 and write access to image buffers. Drivers should support at least
0046 this combination of flags.
0047
0048 ``flags``
0049 The ``flags`` parameter specifies the type of the mapped object,
0050 mapping options and whether modifications made to the mapped copy of
0051 the page are private to the process or are to be shared with other
0052 references.
0053
0054 ``MAP_FIXED`` requests that the driver selects no other address than
0055 the one specified. If the specified address cannot be used,
0056 :c:func:`mmap()` will fail. If ``MAP_FIXED`` is specified,
0057 ``start`` must be a multiple of the pagesize. Use of this option is
0058 discouraged.
0059
0060 One of the ``MAP_SHARED`` or ``MAP_PRIVATE`` flags must be set.
0061 ``MAP_SHARED`` allows applications to share the mapped memory with
0062 other (e. g. child-) processes.
0063
0064 .. note::
0065
0066 The Linux Digital TV applications should not set the
0067 ``MAP_PRIVATE``, ``MAP_DENYWRITE``, ``MAP_EXECUTABLE`` or ``MAP_ANON``
0068 flags.
0069
0070 ``fd``
0071 File descriptor returned by :c:func:`open()`.
0072
0073 ``offset``
0074 Offset of the buffer in device memory, as returned by
0075 :ref:`DMX_QUERYBUF` ioctl.
0076
0077 Description
0078 ===========
0079
0080 The :c:func:`mmap()` function asks to map ``length`` bytes starting at
0081 ``offset`` in the memory of the device specified by ``fd`` into the
0082 application address space, preferably at address ``start``. This latter
0083 address is a hint only, and is usually specified as 0.
0084
0085 Suitable length and offset parameters are queried with the
0086 :ref:`DMX_QUERYBUF` ioctl. Buffers must be allocated with the
0087 :ref:`DMX_REQBUFS` ioctl before they can be queried.
0088
0089 To unmap buffers the :c:func:`munmap()` function is used.
0090
0091 Return Value
0092 ============
0093
0094 On success :c:func:`mmap()` returns a pointer to the mapped buffer. On
0095 error ``MAP_FAILED`` (-1) is returned, and the ``errno`` variable is set
0096 appropriately. Possible error codes are:
0097
0098 EBADF
0099 ``fd`` is not a valid file descriptor.
0100
0101 EACCES
0102 ``fd`` is not open for reading and writing.
0103
0104 EINVAL
0105 The ``start`` or ``length`` or ``offset`` are not suitable. (E. g.
0106 they are too large, or not aligned on a ``PAGESIZE`` boundary.)
0107
0108 The ``flags`` or ``prot`` value is not supported.
0109
0110 No buffers have been allocated with the
0111 :ref:`DMX_REQBUFS` ioctl.
0112
0113 ENOMEM
0114 Not enough physical or virtual memory was available to complete the
0115 request.
