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- .. _DMX_QUERYBUF:
- ******************
- ioctl DMX_QUERYBUF
- ******************
- Name
- ====
- DMX_QUERYBUF - Query the status of a buffer
- .. warning:: this API is still experimental
- Synopsis
- ========
- .. c:function:: int ioctl( int fd, DMX_QUERYBUF, struct dvb_buffer *argp )
- :name: DMX_QUERYBUF
- Arguments
- =========
- ``fd``
- File descriptor returned by :ref:`open() <dmx_fopen>`.
- ``argp``
- Pointer to struct :c:type:`dvb_buffer`.
- Description
- ===========
- This ioctl is part of the mmap streaming I/O method. It can
- be used to query the status of a buffer at any time after buffers have
- been allocated with the :ref:`DMX_REQBUFS` ioctl.
- Applications set the ``index`` field. Valid index numbers range from zero
- to the number of buffers allocated with :ref:`DMX_REQBUFS`
- (struct :c:type:`dvb_requestbuffers` ``count``) minus one.
- After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
- drivers return an error code or fill the rest of the structure.
- On success, the ``offset`` will contain the offset of the buffer from the
- start of the device memory, the ``length`` field its size, and the
- ``bytesused`` the number of bytes occupied by data in the buffer (payload).
- Return Value
- ============
- On success 0 is returned, the ``offset`` will contain the offset of the
- buffer from the start of the device memory, the ``length`` field its size,
- and the ``bytesused`` the number of bytes occupied by data in the buffer
- (payload).
- On error it returns -1 and the ``errno`` variable is set
- appropriately. The generic error codes are described at the
- :ref:`Generic Error Codes <gen-errors>` chapter.
- EINVAL
- The ``index`` is out of bounds.
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