1*4882a593Smuzhiyun.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2*4882a593Smuzhiyun.. c:namespace:: V4L 3*4882a593Smuzhiyun 4*4882a593Smuzhiyun.. _VIDIOC_QUERYBUF: 5*4882a593Smuzhiyun 6*4882a593Smuzhiyun********************* 7*4882a593Smuzhiyunioctl VIDIOC_QUERYBUF 8*4882a593Smuzhiyun********************* 9*4882a593Smuzhiyun 10*4882a593SmuzhiyunName 11*4882a593Smuzhiyun==== 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunVIDIOC_QUERYBUF - Query the status of a buffer 14*4882a593Smuzhiyun 15*4882a593SmuzhiyunSynopsis 16*4882a593Smuzhiyun======== 17*4882a593Smuzhiyun 18*4882a593Smuzhiyun.. c:macro:: VIDIOC_QUERYBUF 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)`` 21*4882a593Smuzhiyun 22*4882a593SmuzhiyunArguments 23*4882a593Smuzhiyun========= 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun``fd`` 26*4882a593Smuzhiyun File descriptor returned by :c:func:`open()`. 27*4882a593Smuzhiyun 28*4882a593Smuzhiyun``argp`` 29*4882a593Smuzhiyun Pointer to struct :c:type:`v4l2_buffer`. 30*4882a593Smuzhiyun 31*4882a593SmuzhiyunDescription 32*4882a593Smuzhiyun=========== 33*4882a593Smuzhiyun 34*4882a593SmuzhiyunThis ioctl is part of the :ref:`streaming <mmap>` I/O method. It can 35*4882a593Smuzhiyunbe used to query the status of a buffer at any time after buffers have 36*4882a593Smuzhiyunbeen allocated with the :ref:`VIDIOC_REQBUFS` ioctl. 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunApplications set the ``type`` field of a struct 39*4882a593Smuzhiyun:c:type:`v4l2_buffer` to the same buffer type as was 40*4882a593Smuzhiyunpreviously used with struct :c:type:`v4l2_format` ``type`` 41*4882a593Smuzhiyunand struct :c:type:`v4l2_requestbuffers` ``type``, 42*4882a593Smuzhiyunand the ``index`` field. Valid index numbers range from zero to the 43*4882a593Smuzhiyunnumber of buffers allocated with 44*4882a593Smuzhiyun:ref:`VIDIOC_REQBUFS` (struct 45*4882a593Smuzhiyun:c:type:`v4l2_requestbuffers` ``count``) minus 46*4882a593Smuzhiyunone. The ``reserved`` and ``reserved2`` fields must be set to 0. When 47*4882a593Smuzhiyunusing the :ref:`multi-planar API <planar-apis>`, the ``m.planes`` 48*4882a593Smuzhiyunfield must contain a userspace pointer to an array of struct 49*4882a593Smuzhiyun:c:type:`v4l2_plane` and the ``length`` field has to be set 50*4882a593Smuzhiyunto the number of elements in that array. After calling 51*4882a593Smuzhiyun:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an 52*4882a593Smuzhiyunerror code or fill the rest of the structure. 53*4882a593Smuzhiyun 54*4882a593SmuzhiyunIn the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``, 55*4882a593Smuzhiyun``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and 56*4882a593Smuzhiyun``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be 57*4882a593Smuzhiyunset to the current I/O method. For the single-planar API, the 58*4882a593Smuzhiyun``m.offset`` contains the offset of the buffer from the start of the 59*4882a593Smuzhiyundevice memory, the ``length`` field its size. For the multi-planar API, 60*4882a593Smuzhiyunfields ``m.mem_offset`` and ``length`` in the ``m.planes`` array 61*4882a593Smuzhiyunelements will be used instead and the ``length`` field of struct 62*4882a593Smuzhiyun:c:type:`v4l2_buffer` is set to the number of filled-in 63*4882a593Smuzhiyunarray elements. The driver may or may not set the remaining fields and 64*4882a593Smuzhiyunflags, they are meaningless in this context. 65*4882a593Smuzhiyun 66*4882a593SmuzhiyunThe struct :c:type:`v4l2_buffer` structure is specified in 67*4882a593Smuzhiyun:ref:`buffer`. 68*4882a593Smuzhiyun 69*4882a593SmuzhiyunReturn Value 70*4882a593Smuzhiyun============ 71*4882a593Smuzhiyun 72*4882a593SmuzhiyunOn success 0 is returned, on error -1 and the ``errno`` variable is set 73*4882a593Smuzhiyunappropriately. The generic error codes are described at the 74*4882a593Smuzhiyun:ref:`Generic Error Codes <gen-errors>` chapter. 75*4882a593Smuzhiyun 76*4882a593SmuzhiyunEINVAL 77*4882a593Smuzhiyun The buffer ``type`` is not supported, or the ``index`` is out of 78*4882a593Smuzhiyun bounds. 79