【genius_platform软件平台开发】第六十五讲：Linux系统之V4L2视频驱动-VIDIOC_STREAMOFF停止取流

VIDIOC_STREAMOFF停止取流

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• 1. 概述
• 2.应用层
• 3. 驱动层

• 3.1 vb2_streamoff 函数
• 3.2 vb2_core_streamoff函数
• 3.2 __vb2_queue_cancel函数
• 3.2 __vb2_dqbuf函数

1. 概述

• 关闭视频流，munmap解除参数start所指向的内存起始地存起始地址。

2.应用层

// 停止视频的采集
    enum v4l2_buf_type unBuffType = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == this->ioCtrl(m_nFd, VIDIOC_STREAMOFF, &unBuffType))
    {
        LOGERROR("CV4l2CaptureIr::stopCapture is error... VIDIOC_STREAMOFF m_unIoMethod=[V4L2_IO_METHOD_MMAP]");
        return ReturnCode_Error;
    }

3. 驱动层

3.1 vb2_streamoff 函数

int vb2_streamoff(struct vb2_queue *q, enum v4l2_buf_type type)
{
 
 
        /*
         * 之前的分析都没有涉及到fileio
         * vivi这部分文章，后续可能会去专门分析
         */        
 
 
	if (vb2_fileio_is_active(q)) {
		dprintk(1, "file io in progress\n");
		return -EBUSY;
	}
	return vb2_core_streamoff(q, type);
}

3.2 vb2_core_streamoff函数

int vb2_core_streamoff(struct vb2_queue *q, unsigned int type)
{
	if (type != q->type) {
		dprintk(1, "invalid stream type\n");
		return -EINVAL;
	}

	/*
	 * Cancel will pause streaming and remove all buffers from the driver
	 * and videobuf, effectively returning control over them to userspace.
	 *
	 * Note that we do this even if q->streaming == 0: if you prepare or
	 * queue buffers, and then call streamoff without ever having called
	 * streamon, you would still expect those buffers to be returned to
	 * their normal dequeued state.
	 */
	__vb2_queue_cancel(q);
	q->waiting_for_buffers = !q->is_output;
	q->last_buffer_dequeued = false;

	dprintk(3, "successful\n");
	return 0;
}
EXPORT_SYMBOL_GPL(vb2_core_streamoff);

3.2 __vb2_queue_cancel函数

/**
 * __vb2_queue_cancel() - cancel and stop (pause) streaming
 *
 * Removes all queued buffers from driver's queue and all buffers queued by
 * userspace from videobuf's queue. Returns to state after reqbufs.
 */
static void __vb2_queue_cancel(struct vb2_queue *q)
{
	unsigned int i;

	/*
	 * Tell driver to stop all transactions and release all queued
	 * buffers.
	 */
	if (q->start_streaming_called)
		call_void_qop(q, stop_streaming, q);

	/*
	 * If you see this warning, then the driver isn't cleaning up properly
	 * in stop_streaming(). See the stop_streaming() documentation in
	 * videobuf2-core.h for more information how buffers should be returned
	 * to vb2 in stop_streaming().
	 */
	if (WARN_ON(atomic_read(&q->owned_by_drv_count))) {
		for (i = 0; i < q->num_buffers; ++i)
			if (q->bufs[i]->state == VB2_BUF_STATE_ACTIVE)
				vb2_buffer_done(q->bufs[i], VB2_BUF_STATE_ERROR);
		/* Must be zero now */
		WARN_ON(atomic_read(&q->owned_by_drv_count));
	}

	// 重置各种数据成员
	q->streaming = 0;
	q->start_streaming_called = 0;
	q->queued_count = 0;
	q->error = 0;

	// 清空queued_list
	/*
	 * Remove all buffers from videobuf's list...
	 */
	INIT_LIST_HEAD(&q->queued_list);
	
	// 清空done_list
	/*
	 * ...and done list; userspace will not receive any buffers it
	 * has not already dequeued before initiating cancel.
	 */
	INIT_LIST_HEAD(&q->done_list);
	//设置owned_by_drv_count为0
	atomic_set(&q->owned_by_drv_count, 0);
	//  唤醒等待线程
	/*
     * 可能如下？
     * 1.其他应用在使用poll
     * 2.其他应用在dqbuf
     */
	wake_up_all(&q->done_wq);

	/*
	 * Reinitialize all buffers for next use.
	 * Make sure to call buf_finish for any queued buffers. Normally
	 * that's done in dqbuf, but that's not going to happen when we
	 * cancel the whole queue. Note: this code belongs here, not in
	 * __vb2_dqbuf() since in vb2_core_dqbuf() there is a critical
	 * call to __fill_user_buffer() after buf_finish(). That order can't
	 * be changed, so we can't move the buf_finish() to __vb2_dqbuf().
	 */
	for (i = 0; i < q->num_buffers; ++i) {
		struct vb2_buffer *vb = q->bufs[i];

		if (vb->state == VB2_BUF_STATE_PREPARED ||
		    vb->state == VB2_BUF_STATE_QUEUED) {
			unsigned int plane;

			for (plane = 0; plane < vb->num_planes; ++plane)
				call_void_memop(vb, finish,
						vb->planes[plane].mem_priv);
		}

		if (vb->state != VB2_BUF_STATE_DEQUEUED) {
			vb->state = VB2_BUF_STATE_PREPARED;
			call_void_vb_qop(vb, buf_finish, vb);
		}
		__vb2_dqbuf(vb);
	}
}

3.2 __vb2_dqbuf函数

/**
 * __vb2_dqbuf() - bring back the buffer to the DEQUEUED state
 */
static void __vb2_dqbuf(struct vb2_buffer *vb)
{
	struct vb2_queue *q = vb->vb2_queue;
	unsigned int i;

	// 检查状态是否为出队列了
	/* nothing to do if the buffer is already dequeued */
	if (vb->state == VB2_BUF_STATE_DEQUEUED)
		return;

	//设置出队列状态VB2_BUF_STATE_DEQUEUED
	vb->state = VB2_BUF_STATE_DEQUEUED;

	//unmap 释放内存
	/* unmap DMABUF buffer */
	if (q->memory == VB2_MEMORY_DMABUF)
		for (i = 0; i < vb->num_planes; ++i) {
			if (!vb->planes[i].dbuf_mapped)
				continue;
			call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
			vb->planes[i].dbuf_mapped = 0;
		}
}

• 注意：
  在执行完off之后其实几个相关队列中的buffer都被清理了，所以再次执行on的时候需要重新reqbuffer、qbuf等操作。