ioctl VIDIOC_QUERYBUF &manvol; VIDIOC_QUERYBUF Query the status of a buffer int ioctl int fd int request struct v4l2_buffer *argp fd &fd; request VIDIOC_QUERYBUF argp 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 &VIDIOC-REQBUFS; ioctl. Applications set the type field of a &v4l2-buffer; to the same buffer type as was previously used with &v4l2-format; type and &v4l2-requestbuffers; type, and the index field. Valid index numbers range from zero to the number of buffers allocated with &VIDIOC-REQBUFS; (&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 &v4l2-plane; and the length field has to be set to the number of elements in that array. After calling 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 &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 v4l2_buffer structure is specified in . &return-value; EINVAL The buffer type is not supported, or the index is out of bounds.