Hello,
On Mon, Mar 04, 2019 at 03:36:32PM +0000, Kieran Bingham wrote:
> On 04/03/2019 12:35, Hugues Fruchet wrote:
> > Add support of read() call from userspace by implementing
> > uvc_v4l2_read() with vb2_read() helper.
>
> Just thinking out loud,
>
> This opens up UVC devices to read raw full frame images through this
> interface as well.
>
> Due to the UVC protocol, there is /already/ a full memcpy to get these
> images out of the URB packets, so using a read() interface would be
> another full frame copy.
>
> I can perhaps see the usecase for reading compressed data through this
> interface - but full frames don't seem appropriate. (not impossible of
> course, just is it reasonable?)
>
> If this is to be enabled, should it be enabled for compressed formats
> only? or would that complicate matters?
I've repeatedly refused read() support in uvcvideo for this reason, and
also because read() doesn't carry framing information very well. It's
just not a good API for capturing video frames from a webcam, and so far
I haven't heard a compeling reason why it should be enabled. I thus
haven't changed my mind :-)
> > Signed-off-by: Hugues Fruchet <hugues.fruchet@xxxxxx>
> > ---
> > drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
> > drivers/media/usb/uvc/uvc_v4l2.c | 11 ++++++++---
> > drivers/media/usb/uvc/uvcvideo.h | 2 ++
> > 3 files changed, 24 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> > index 682698e..0c8a0a8 100644
> > --- a/drivers/media/usb/uvc/uvc_queue.c
> > +++ b/drivers/media/usb/uvc/uvc_queue.c
> > @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
> > int ret;
> >
> > queue->queue.type = type;
> > - queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> > + queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
> > queue->queue.drv_priv = queue;
> > queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
> > queue->queue.mem_ops = &vb2_vmalloc_memops;
> > @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
> > return ret;
> > }
> >
> > +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> > + char __user *buf, size_t count, loff_t *ppos)
> > +{
> > + ssize_t ret;
> > +
> > + mutex_lock(&queue->mutex);
> > + ret = vb2_read(&queue->queue, buf, count, ppos,
> > + file->f_flags & O_NONBLOCK);
> > + mutex_unlock(&queue->mutex);
> > +
> > + return ret;
> > +}
> > +
> > int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
> > {
> > return vb2_mmap(&queue->queue, vma);
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index 84be596..3866832 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
> > strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
> > strscpy(cap->card, vdev->name, sizeof(cap->card));
> > usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> > - cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> > + cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> > + V4L2_CAP_READWRITE
> > | chain->caps;
> >
> > return 0;
> > @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
> > static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
> > size_t count, loff_t *ppos)
> > {
> > - uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> > - return -EINVAL;
> > + struct uvc_fh *handle = file->private_data;
> > + struct uvc_streaming *stream = handle->stream;
> > +
> > + uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> > +
> > + return uvc_queue_read(&stream->queue, file, data, count, ppos);
> > }
> >
> > static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index c7c1baa..5d0515c 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
> > struct uvc_buffer *buf);
> > struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
> > void uvc_queue_buffer_release(struct uvc_buffer *buf);
> > +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> > + char __user *buf, size_t count, loff_t *ppos);
> > int uvc_queue_mmap(struct uvc_video_queue *queue,
> > struct vm_area_struct *vma);
> > __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
--
Regards,
Laurent Pinchart
