1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2 .. c:namespace:: DTV.dmx
3
4 .. _dmx-mmap:
5
6 *****************
7 Digital TV mmap()
8 *****************
9
10 Name
11 ====
12
13 dmx-mmap - Map device memory into application
14
15 .. warning:: this API is still experimental
16
17 Synopsis
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_
26
27 Arguments
28 =========
29
30 ``start``
31 Map the buffer to this address in the appl
32 When the ``MAP_FIXED`` flag is specified,
33 multiple of the pagesize and mmap will fai
34 address cannot be used. Use of this option
35 applications should just specify a ``NULL`
36
37 ``length``
38 Length of the memory area to map. This mus
39 DVB packet length (188, on most drivers).
40
41 ``prot``
42 The ``prot`` argument describes the desire
43 Regardless of the device type and the dire
44 should be set to ``PROT_READ`` | ``PROT_WR
45 and write access to image buffers. Drivers
46 this combination of flags.
47
48 ``flags``
49 The ``flags`` parameter specifies the type
50 mapping options and whether modifications
51 the page are private to the process or are
52 references.
53
54 ``MAP_FIXED`` requests that the driver sel
55 the one specified. If the specified addres
56 :c:func:`mmap()` will fail. If ``MAP_FIXED
57 ``start`` must be a multiple of the pagesi
58 discouraged.
59
60 One of the ``MAP_SHARED`` or ``MAP_PRIVATE
61 ``MAP_SHARED`` allows applications to shar
62 other (e. g. child-) processes.
63
64 .. note::
65
66 The Linux Digital TV applications shoul
67 ``MAP_PRIVATE``, ``MAP_DENYWRITE``, ``M
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
75 :ref:`DMX_QUERYBUF` ioctl.
76
77 Description
78 ===========
79
80 The :c:func:`mmap()` function asks to map ``le
81 ``offset`` in the memory of the device specifi
82 application address space, preferably at addre
83 address is a hint only, and is usually specifi
84
85 Suitable length and offset parameters are quer
86 :ref:`DMX_QUERYBUF` ioctl. Buffers must be all
87 :ref:`DMX_REQBUFS` ioctl before they can be qu
88
89 To unmap buffers the :c:func:`munmap()` functi
90
91 Return Value
92 ============
93
94 On success :c:func:`mmap()` returns a pointer
95 error ``MAP_FAILED`` (-1) is returned, and the
96 appropriately. Possible error codes are:
97
98 EBADF
99 ``fd`` is not a valid file descriptor.
100
101 EACCES
102 ``fd`` is not open for reading and writing
103
104 EINVAL
105 The ``start`` or ``length`` or ``offset``
106 they are too large, or not aligned on a ``
107
108 The ``flags`` or ``prot`` value is not sup
109
110 No buffers have been allocated with the
111 :ref:`DMX_REQBUFS` ioctl.
112
113 ENOMEM
114 Not enough physical or virtual memory was
115 request.
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