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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2.. c:namespace:: DTV.dmx3 4.. _DMX_QUERYBUF:5 6******************7ioctl DMX_QUERYBUF8******************9 10Name11====12 13DMX_QUERYBUF - Query the status of a buffer14 15.. warning:: this API is still experimental16 17Synopsis18========19 20.. c:macro:: DMX_QUERYBUF21 22``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)``23 24Arguments25=========26 27``fd``28 File descriptor returned by :c:func:`open()`.29 30``argp``31 Pointer to struct :c:type:`dvb_buffer`.32 33Description34===========35 36This ioctl is part of the mmap streaming I/O method. It can37be used to query the status of a buffer at any time after buffers have38been allocated with the :ref:`DMX_REQBUFS` ioctl.39 40Applications set the ``index`` field. Valid index numbers range from zero41to 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 the48start of the device memory, the ``length`` field its size, and the49``bytesused`` the number of bytes occupied by data in the buffer (payload).50 51Return Value52============53 54On success 0 is returned, the ``offset`` will contain the offset of the55buffer from the start of the device memory, the ``length`` field its size,56and the ``bytesused`` the number of bytes occupied by data in the buffer57(payload).58 59On error it returns -1 and the ``errno`` variable is set60appropriately. The generic error codes are described at the61:ref:`Generic Error Codes <gen-errors>` chapter.62 63EINVAL64 The ``index`` is out of bounds.65