dmx-querybuf.rst (1725B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: DTV.dmx 3 4.. _DMX_QUERYBUF: 5 6****************** 7ioctl DMX_QUERYBUF 8****************** 9 10Name 11==== 12 13DMX_QUERYBUF - Query the status of a buffer 14 15.. warning:: this API is still experimental 16 17Synopsis 18======== 19 20.. c:macro:: DMX_QUERYBUF 21 22``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)`` 23 24Arguments 25========= 26 27``fd`` 28 File descriptor returned by :c:func:`open()`. 29 30``argp`` 31 Pointer to struct :c:type:`dvb_buffer`. 32 33Description 34=========== 35 36This ioctl is part of the mmap streaming I/O method. It can 37be used to query the status of a buffer at any time after buffers have 38been allocated with the :ref:`DMX_REQBUFS` ioctl. 39 40Applications set the ``index`` field. Valid index numbers range from zero 41to the number of buffers allocated with :ref:`DMX_REQBUFS` 42(struct :c:type:`dvb_requestbuffers` ``count``) minus one. 43 44After calling :ref:`DMX_QUERYBUF` with a pointer to this structure, 45drivers return an error code or fill the rest of the structure. 46 47On success, the ``offset`` will contain the offset of the buffer from the 48start 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 51Return Value 52============ 53 54On success 0 is returned, the ``offset`` will contain the offset of the 55buffer from the start of the device memory, the ``length`` field its size, 56and the ``bytesused`` the number of bytes occupied by data in the buffer 57(payload). 58 59On error it returns -1 and the ``errno`` variable is set 60appropriately. The generic error codes are described at the 61:ref:`Generic Error Codes <gen-errors>` chapter. 62 63EINVAL 64 The ``index`` is out of bounds.