.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later .. c:namespace:: V4L .. _VIDIOC_QUERYBUF: ********************* ioctl VIDIOC_QUERYBUF ********************* Name ==== VIDIOC_QUERYBUF - Query the status of a buffer Synopsis ======== .. c:macro:: VIDIOC_QUERYBUF ``int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)`` Arguments ========= ``fd`` File descriptor returned by :c:func:`open()`. ``argp`` Pointer to struct :c:type:`v4l2_buffer`. Description =========== This ioctl is part of the :ref:`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:`VIDIOC_REQBUFS` ioctl. Applications set the ``type`` field of a struct :c:type:`v4l2_buffer` to the same buffer type as was previously used with struct :c:type:`v4l2_format` ``type`` and struct :c:type:`v4l2_requestbuffers` ``type``, and the ``index`` field. Valid index numbers range from zero to the number of buffers allocated with :ref:`VIDIOC_REQBUFS` (struct :c:type:`v4l2_requestbuffers` ``count``) minus one. The ``reserved`` and ``reserved2`` fields must be set to 0. When using the :ref:`multi-planar API `, the ``m.planes`` field must contain a userspace pointer to an array of struct :c:type:`v4l2_plane` and the ``length`` field has to be set to the number of elements in that array. After calling :ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an error code or fill the rest of the structure. In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``, ``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``memory`` field will be set to the current I/O method. For the single-planar API, the ``m.offset`` contains the offset of the buffer from the start of the device memory, the ``length`` field its size. For the multi-planar API, fields ``m.mem_offset`` and ``length`` in the ``m.planes`` array elements will be used instead and the ``length`` field of struct :c:type:`v4l2_buffer` is set to the number of filled-in array elements. The driver may or may not set the remaining fields and flags, they are meaningless in this context. The struct :c:type:`v4l2_buffer` structure is specified in :ref:`buffer`. Return Value ============ On success 0 is returned, on error -1 and the ``errno`` variable is set appropriately. The generic error codes are described at the :ref:`Generic Error Codes ` chapter. EINVAL The buffer ``type`` is not supported, or the ``index`` is out of bounds.