VIDIOC_QUERYBUF - Query the status of a buffer
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.
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.