7.47. ioctl VIDIOC_QUERYBUF

7.47.1. Name

VIDIOC_QUERYBUF - Query the status of a buffer

7.47.2. Synopsis

int ioctl(int fd, VIDIOC_QUERYBUF, struct v4l2_buffer *argp)

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 type is not supported, or the index is out of bounds.