8.47. ioctl VIDIOC_QUERYBUF¶
8.47.1. Name¶
VIDIOC_QUERYBUF - Query the status of a buffer
8.47.4. Description¶
This ioctl is part of the 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 ioctl VIDIOC_REQBUFS ioctl.
Applications set the type
field of a struct
v4l2_buffer to the same buffer type as was
previously used with struct v4l2_format type
and struct v4l2_requestbuffers type
,
and the index
field. Valid index numbers range from zero to the
number of buffers allocated with
ioctl VIDIOC_REQBUFS (struct
v4l2_requestbuffers count
) minus
one. The reserved
and reserved2
fields must be set to 0. When
using the multi-planar API, the m.planes
field must contain a userspace pointer to an array of struct
v4l2_plane and the length
field has to be set
to the number of elements in that array. After calling
ioctl 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
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 v4l2_buffer structure is specified in Buffers.
8.47.5. 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
Generic Error Codes chapter.
- EINVAL
- The buffer
type
is not supported, or theindex
is out of bounds.