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