应用层：
case IO_METHOD_MMAP:
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
switch (errno) {
case EAGAIN:
return 0;
case EIO:
default:
errno_exit("VIDIOC_DQBUF");
}
}
assert(buf.index < n_buffers);
camera_inf->buf_vaddr = (void *)buffers[buf.index].start;
if (camera_ctl->cam_opt == OPS_PREVIEW)
{
if (camera_ctl->ops.priview_picture){
camera_ctl->ops.priview_picture(camera_inf);
}
} else if (camera_ctl->cam_opt == OPS_CAPTURE){
if (camera_ctl->ops.capture_picture)
camera_ctl->ops.capture_picture(camera_inf, camera_ctl);
}
if (camera_inf->param.debug == 1 && camera_ctl->cam_opt == OPS_PREVIEW)
{
if (camera_ctl->ops.camera_fps)
camera_ctl->ops.camera_fps(camera_inf);
}
if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
内核:
(1)
drivers/media/v4l2-core/v4l2-ioctl.c
IOCTL_INFO_FNC(VIDIOC_DQBUF, v4l_dqbuf, v4l_print_buffer, INFO_FL_QUEUE)
static int v4l_dqbuf(const struct v4l2_ioctl_ops *ops,
struct file *file, void *fh, void *arg)
{
struct v4l2_buffer *p = arg;
int ret = check_fmt(file, p->type);
return ret ? ret : ops->vidioc_dqbuf(file, fh, p);
}
(2)
drivers/media/platform/soc_camera/soc_camera.c
static int soc_camera_dqbuf(struct file *file, void *priv,
struct v4l2_buffer *p)
{
struct soc_camera_device *icd = file->private_data;
struct soc_camera_host *ici = to_soc_camera_host(icd->parent);
WARN_ON(priv != file->private_data);
if (icd->streamer != file)
return -EBUSY;
if (ici->ops->init_videobuf)
return videobuf_dqbuf(&icd->vb_vidq, p, file->f_flags & O_NONBLOCK);
else
return vb2_dqbuf(&icd->vb2_vidq, p, file->f_flags & O_NONBLOCK);
}
(3)
drivers/media/v4l2-core/videobuf2-core.c
int vb2_dqbuf(struct vb2_queue *q, struct v4l2_buffer *b, bool nonblocking)
{
ret = __vb2_get_done_vb(q, &vb, b, nonblocking); //从done_list的链表中取出buffer 然后删除buffer list_del(&(*vb)->done_entry);
ret = call_qop(q, buf_finish, vb);
/* Fill buffer information for the userspace */
__fill_v4l2_buffer(vb, b); //填充v4l2_buffer结构体返回给应用层
/* Remove from videobuf queue */
list_del(&vb->queued_entry); //删除queued_list链表的一个节点。
/* go back to dequeued state */
__vb2_dqbuf(vb);
}
(3)
VIDIOC_QBUF 入队一个buffer