On 06/06/2014 03:53 PM, Laurent Pinchart wrote:
> When a fatal error occurs that render the device unusable, the only
> options for a driver to signal the error condition to userspace is to
> set the V4L2_BUF_FLAG_ERROR flag when dequeuing buffers and to return an
> error from the buffer prepare handler when queuing buffers.
>
> The buffer error flag indicates a transient error and can't be used by
> applications to detect fatal errors. Returning an error from vb2_qbuf()
> is thus the only real indication that a fatal error occurred. However,
> this is difficult to handle for multithreaded applications that requeue
> buffers from a thread other than the control thread. In particular the
> poll() call in the control thread will not notify userspace of the
> error.
>
> This patch adds an explicit mechanism to report fatal errors to
> userspace. Drivers can call the vb2_queue_error() function to signal a
> fatal error. From this moment on, buffer preparation will return -EIO to
> userspace, and vb2_poll() will set the POLLERR flag and return
> immediately. The error flag is cleared when cancelling the queue, either
> at stream off time (through vb2_streamoff) or when releasing the queue
> with vb2_queue_release().
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Regards,
Hans
> ---
> drivers/media/v4l2-core/videobuf2-core.c | 39 +++++++++++++++++++++++++++++---
> include/media/videobuf2-core.h | 3 +++
> 2 files changed, 39 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index a05f355..b1b7f78 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1582,6 +1582,11 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
> return -EINVAL;
> }
>
> + if (q->error) {
> + dprintk(1, "fatal error occurred on queue\n");
> + return -EIO;
> + }
> +
> vb->state = VB2_BUF_STATE_PREPARING;
> vb->v4l2_buf.timestamp.tv_sec = 0;
> vb->v4l2_buf.timestamp.tv_usec = 0;
> @@ -1877,6 +1882,11 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
> return -EINVAL;
> }
>
> + if (q->error) {
> + dprintk(1, "Queue in error state, will not wait for buffers\n");
> + return -EIO;
> + }
> +
> if (!list_empty(&q->done_list)) {
> /*
> * Found a buffer that we were waiting for.
> @@ -1902,7 +1912,8 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
> */
> dprintk(3, "will sleep waiting for buffers\n");
> ret = wait_event_interruptible(q->done_wq,
> - !list_empty(&q->done_list) || !q->streaming);
> + !list_empty(&q->done_list) || !q->streaming ||
> + q->error);
>
> /*
> * We need to reevaluate both conditions again after reacquiring
> @@ -2099,6 +2110,7 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
> q->streaming = 0;
> q->start_streaming_called = 0;
> q->queued_count = 0;
> + q->error = 0;
>
> /*
> * Remove all buffers from videobuf's list...
> @@ -2176,6 +2188,27 @@ static int vb2_internal_streamon(struct vb2_queue *q, enum v4l2_buf_type type)
> }
>
> /**
> + * vb2_queue_error() - signal a fatal error on the queue
> + * @q: videobuf2 queue
> + *
> + * Flag that a fatal unrecoverable error has occurred and wake up all processes
> + * waiting on the queue. Polling will now set POLLERR and queuing and dequeuing
> + * buffers will return -EIO.
> + *
> + * The error flag will be cleared when cancelling the queue, either from
> + * vb2_streamoff or vb2_queue_release. Drivers should thus not call this
> + * function before starting the stream, otherwise the error flag will remain set
> + * until the queue is released when closing the device node.
> + */
> +void vb2_queue_error(struct vb2_queue *q)
> +{
> + q->error = 1;
> +
> + wake_up_all(&q->done_wq);
> +}
> +EXPORT_SYMBOL_GPL(vb2_queue_error);
> +
> +/**
> * vb2_streamon - start streaming
> * @q: videobuf2 queue
> * @type: type argument passed from userspace to vidioc_streamon handler
> @@ -2534,9 +2567,9 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
>
> /*
> * There is nothing to wait for if no buffer has been queued and the
> - * queue isn't streaming.
> + * queue isn't streaming, or if the error flag is set.
> */
> - if (list_empty(&q->queued_list) && !vb2_is_streaming(q))
> + if ((list_empty(&q->queued_list) && !vb2_is_streaming(q)) || q->error)
> return res | POLLERR;
>
> if (list_empty(&q->done_list))
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index bca25dc..e5cb2a3 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -375,6 +375,7 @@ struct v4l2_fh;
> * @streaming: current streaming state
> * @start_streaming_called: start_streaming() was called successfully and we
> * started streaming.
> + * @error: a fatal error occurred on the queue
> * @fileio: file io emulator internal data, used only if emulator is active
> * @threadio: thread io internal data, used only if thread is active
> */
> @@ -411,6 +412,7 @@ struct vb2_queue {
>
> unsigned int streaming:1;
> unsigned int start_streaming_called:1;
> + unsigned int error:1;
>
> struct vb2_fileio_data *fileio;
> struct vb2_threadio_data *threadio;
> @@ -443,6 +445,7 @@ int vb2_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b);
> int __must_check vb2_queue_init(struct vb2_queue *q);
>
> void vb2_queue_release(struct vb2_queue *q);
> +void vb2_queue_error(struct vb2_queue *q);
>
> int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b);
> int vb2_expbuf(struct vb2_queue *q, struct v4l2_exportbuffer *eb);
>
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