Documentation/userspace-api/media/v4l/vidioc-querybuf.rst
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later .. c:namespace:: V4L
.. _VIDIOC_QUERYBUF:
ioctl VIDIOC_QUERYBUF
VIDIOC_QUERYBUF - Query the status of a buffer
.. c:macro:: VIDIOC_QUERYBUF
int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)
fd
File descriptor returned by :c:func:open().
argp
Pointer to struct :c:type:v4l2_buffer.
This ioctl is part of the :ref:streaming <mmap> 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 <planar-apis>, 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.
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 <gen-errors> chapter.
EINVAL
The buffer type is not supported, or the index is out of
bounds.