1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: DTV.dmx
13 DMX_QUERYBUF - Query the status of a buffer
15 .. warning:: this API is still experimental
20 .. c:macro:: DMX_QUERYBUF
22 ``int ioctl(int fd, DMX_QUERYBUF, struct dvb_buffer *argp)``
28 File descriptor returned by :c:func:`open()`.
31 Pointer to struct :c:type:`dvb_buffer`.
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.
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.
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.
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).
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
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.
64 The ``index`` is out of bounds.