7.47. ioctl VIDIOC_QUERYBUF¶
VIDIOC_QUERYBUF - Query the status of a buffer
ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)¶
- File descriptor returned by open().
- Pointer to struct
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
index field. Valid index numbers range from zero to the
number of buffers allocated with
ioctl VIDIOC_REQBUFS (struct
reserved2 fields must be set to 0. When
using the multi-planar API, the
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.
flags field the
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,
length in the
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.
v4l2_buffer structure is specified in
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.
- The buffer
typeis not supported, or the
indexis out of bounds.