.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: DTV.dmx
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.. _DMX_QUERYBUF:
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******************
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ioctl DMX_QUERYBUF
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******************
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Name
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====
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DMX_QUERYBUF - Query the status of a buffer
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.. warning:: this API is still experimental
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Synopsis
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========
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.. c:macro:: DMX_QUERYBUF
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``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)``
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open()`.
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``argp``
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Pointer to struct :c:type:`dvb_buffer`.
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Description
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===========
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This ioctl is part of the mmap streaming I/O method. It can
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be used to query the status of a buffer at any time after buffers have
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been allocated with the :ref:`DMX_REQBUFS` ioctl.
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Applications set the ``index`` field. Valid index numbers range from zero
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to the number of buffers allocated with :ref:`DMX_REQBUFS`
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(struct :c:type:`dvb_requestbuffers` ``count``) minus one.
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After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
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drivers return an error code or fill the rest of the structure.
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On success, the ``offset`` will contain the offset of the buffer from the
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start of the device memory, the ``length`` field its size, and the
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``bytesused`` the number of bytes occupied by data in the buffer (payload).
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Return Value
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============
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On success 0 is returned, the ``offset`` will contain the offset of the
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buffer from the start of the device memory, the ``length`` field its size,
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and the ``bytesused`` the number of bytes occupied by data in the buffer
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(payload).
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On error it returns -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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The ``index`` is out of bounds.
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