1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 .. c:namespace:: DTV.dmx 3 4 .. _DMX_QUERYBUF: 5 6 ****************** 7 ioctl DMX_QUERYBUF 8 ****************** 9 10 Name 11 ==== 12 13 DMX_QUERYBUF - Query the status of a buffer 14 15 .. warning:: this API is still experimental 16 17 Synopsis 18 ======== 19 20 .. c:macro:: DMX_QUERYBUF 21 22 ``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)`` 23 24 Arguments 25 ========= 26 27 ``fd`` 28 File descriptor returned by :c:func:`open()`. 29 30 ``argp`` 31 Pointer to struct :c:type:`dvb_buffer`. 32 33 Description 34 =========== 35 36 This ioctl is part of the mmap streaming I/O method. It can 37 be used to query the status of a buffer at any time after buffers have 38 been allocated with the :ref:`DMX_REQBUFS` ioctl. 39 40 Applications set the ``index`` field. Valid index numbers range from zero 41 to the number of buffers allocated with :ref:`DMX_REQBUFS` 42 (struct :c:type:`dvb_requestbuffers` ``count``) minus one. 43 44 After calling :ref:`DMX_QUERYBUF` with a pointer to this structure, 45 drivers return an error code or fill the rest of the structure. 46 47 On success, the ``offset`` will contain the offset of the buffer from the 48 start of the device memory, the ``length`` field its size, and the 49 ``bytesused`` the number of bytes occupied by data in the buffer (payload). 50 51 Return Value 52 ============ 53 54 On success 0 is returned, the ``offset`` will contain the offset of the 55 buffer from the start of the device memory, the ``length`` field its size, 56 and the ``bytesused`` the number of bytes occupied by data in the buffer 57 (payload). 58 59 On error it returns -1 and the ``errno`` variable is set 60 appropriately. The generic error codes are described at the 61 :ref:`Generic Error Codes <gen-errors>` chapter. 62 63 EINVAL 64 The ``index`` is out of bounds.
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