7.47. ioctl VIDIOC_QUERYBUF¶
7.47.1. Name¶
VIDIOC_QUERYBUF - Query the status of a buffer
7.47.3. Arguments¶
fd- File descriptor returned by
open(). argp- Pointer to struct
v4l2_buffer.
7.47.4. 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.
7.47.5. 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
typeis not supported, or theindexis out of bounds.