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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2.. c:namespace:: DTV.dmx3 4.. _dmx-mmap:5 6*****************7Digital TV mmap()8*****************9 10Name11====12 13dmx-mmap - Map device memory into application address space14 15.. warning:: this API is still experimental16 17Synopsis18========19 20.. code-block:: c21 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 27Arguments28=========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 a33 multiple of the pagesize and mmap will fail when the specified34 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 the39 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 it44 should be set to ``PROT_READ`` | ``PROT_WRITE``, permitting read45 and write access to image buffers. Drivers should support at least46 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 of51 the page are private to the process or are to be shared with other52 references.53 54 ``MAP_FIXED`` requests that the driver selects no other address than55 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 is58 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 with62 other (e. g. child-) processes.63 64 .. note::65 66 The Linux Digital TV applications should not set the67 ``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 by75 :ref:`DMX_QUERYBUF` ioctl.76 77Description78===========79 80The :c:func:`mmap()` function asks to map ``length`` bytes starting at81``offset`` in the memory of the device specified by ``fd`` into the82application address space, preferably at address ``start``. This latter83address is a hint only, and is usually specified as 0.84 85Suitable length and offset parameters are queried with the86:ref:`DMX_QUERYBUF` ioctl. Buffers must be allocated with the87:ref:`DMX_REQBUFS` ioctl before they can be queried.88 89To unmap buffers the :c:func:`munmap()` function is used.90 91Return Value92============93 94On success :c:func:`mmap()` returns a pointer to the mapped buffer. On95error ``MAP_FAILED`` (-1) is returned, and the ``errno`` variable is set96appropriately. Possible error codes are:97 98EBADF99 ``fd`` is not a valid file descriptor.100 101EACCES102 ``fd`` is not open for reading and writing.103 104EINVAL105 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 the111 :ref:`DMX_REQBUFS` ioctl.112 113ENOMEM114 Not enough physical or virtual memory was available to complete the115 request.116