1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: DTV.dmx 3 4.. _dmx-mmap: 5 6***************** 7Digital TV mmap() 8***************** 9 10Name 11==== 12 13dmx-mmap - Map device memory into application address space 14 15.. warning:: this API is still experimental 16 17Synopsis 18======== 19 20.. code-block:: c 21 22 #include <unistd.h> 23 #include <sys/mman.h> 24 25.. c:function:: void *mmap( void *start, size_t length, int prot, int flags, int fd, off_t offset ) 26 27Arguments 28========= 29 30``start`` 31 Map the buffer to this address in the application's address space. 32 When the ``MAP_FIXED`` flag is specified, ``start`` must be a 33 multiple of the pagesize and mmap will fail when the specified 34 address cannot be used. Use of this option is discouraged; 35 applications should just specify a ``NULL`` pointer here. 36 37``length`` 38 Length of the memory area to map. This must be a multiple of the 39 DVB packet length (188, on most drivers). 40 41``prot`` 42 The ``prot`` argument describes the desired memory protection. 43 Regardless of the device type and the direction of data exchange it 44 should be set to ``PROT_READ`` | ``PROT_WRITE``, permitting read 45 and write access to image buffers. Drivers should support at least 46 this combination of flags. 47 48``flags`` 49 The ``flags`` parameter specifies the type of the mapped object, 50 mapping options and whether modifications made to the mapped copy of 51 the page are private to the process or are to be shared with other 52 references. 53 54 ``MAP_FIXED`` requests that the driver selects no other address than 55 the one specified. If the specified address cannot be used, 56 :c:func:`mmap()` will fail. If ``MAP_FIXED`` is specified, 57 ``start`` must be a multiple of the pagesize. Use of this option is 58 discouraged. 59 60 One of the ``MAP_SHARED`` or ``MAP_PRIVATE`` flags must be set. 61 ``MAP_SHARED`` allows applications to share the mapped memory with 62 other (e. g. child-) processes. 63 64 .. note:: 65 66 The Linux Digital TV applications should not set the 67 ``MAP_PRIVATE``, ``MAP_DENYWRITE``, ``MAP_EXECUTABLE`` or ``MAP_ANON`` 68 flags. 69 70``fd`` 71 File descriptor returned by :c:func:`open()`. 72 73``offset`` 74 Offset of the buffer in device memory, as returned by 75 :ref:`DMX_QUERYBUF` ioctl. 76 77Description 78=========== 79 80The :c:func:`mmap()` function asks to map ``length`` bytes starting at 81``offset`` in the memory of the device specified by ``fd`` into the 82application address space, preferably at address ``start``. This latter 83address is a hint only, and is usually specified as 0. 84 85Suitable length and offset parameters are queried with the 86:ref:`DMX_QUERYBUF` ioctl. Buffers must be allocated with the 87:ref:`DMX_REQBUFS` ioctl before they can be queried. 88 89To unmap buffers the :c:func:`munmap()` function is used. 90 91Return Value 92============ 93 94On success :c:func:`mmap()` returns a pointer to the mapped buffer. On 95error ``MAP_FAILED`` (-1) is returned, and the ``errno`` variable is set 96appropriately. Possible error codes are: 97 98EBADF 99 ``fd`` is not a valid file descriptor. 100 101EACCES 102 ``fd`` is not open for reading and writing. 103 104EINVAL 105 The ``start`` or ``length`` or ``offset`` are not suitable. (E. g. 106 they are too large, or not aligned on a ``PAGESIZE`` boundary.) 107 108 The ``flags`` or ``prot`` value is not supported. 109 110 No buffers have been allocated with the 111 :ref:`DMX_REQBUFS` ioctl. 112 113ENOMEM 114 Not enough physical or virtual memory was available to complete the 115 request. 116