On Tue, Nov 10, 2020 at 10:56:05AM +0100, Thomas Hämmerle wrote:
> On 10.11.20 09:40, Greg KH wrote:
> > On Tue, Nov 10, 2020 at 09:25:04AM +0100, thomas.haemmerle@xxxxxxxxxxxxxx wrote:
> > > From: Thomas Haemmerle <thomas.haemmerle@xxxxxxxxxxxxxx>
> > >
> > > Currently, the UVC function is activated when open on the corresponding
> > > v4l2 device is called.
> > > On another open the activation of the function fails since the
> > > deactivation counter in `usb_function_activate` equals 0. However the
> > > error is not returned to userspace since the open of the v4l2 device is
> > > successful.
> > >
> > > On a close the function is deactivated (since deactivation counter still
> > > equals 0) and the video is disabled in `uvc_v4l2_release`, although
> > > another process potentially is streaming.
> > >
> > > Move activation of UVC function to subscription on UVC_EVENT_SETUP and
> > > keep track of the number of subscribers (limited to 1) because there we
> > > can guarantee for a userspace program utilizing UVC.
> > > Extend the `struct uvc_file_handle` with member `bool connected` to tag
> > > it for a deactivation of the function.
> > >
> > > With this a process is able to check capabilities of the v4l2 device
> > > without deactivating the function for another process actually using the
> > > device for UVC streaming.
> > >
> > > Signed-off-by: Thomas Haemmerle <thomas.haemmerle@xxxxxxxxxxxxxx>
> > > ---
> > > v2:
> > > - fix deadlock in `uvc_v4l2_unsubscribe_event()` (mutex is already
> > > locked in v4l2-core) introduced in v1
> > > - lock mutex in `uvc_v4l2_release()` to suppress ioctls and protect
> > > connected
> > >
> > > drivers/usb/gadget/function/uvc.h | 2 +
> > > drivers/usb/gadget/function/uvc_v4l2.c | 56 +++++++++++++++++++++-----
> > > 2 files changed, 48 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> > > index 73da4f9a8d4c..0d0bcbffc8fd 100644
> > > --- a/drivers/usb/gadget/function/uvc.h
> > > +++ b/drivers/usb/gadget/function/uvc.h
> > > @@ -117,6 +117,7 @@ struct uvc_device {
> > > enum uvc_state state;
> > > struct usb_function func;
> > > struct uvc_video video;
> > > + unsigned int connections;
> > > /* Descriptors */
> > > struct {
> > > @@ -147,6 +148,7 @@ static inline struct uvc_device *to_uvc(struct usb_function *f)
> > > struct uvc_file_handle {
> > > struct v4l2_fh vfh;
> > > struct uvc_video *device;
> > > + bool connected;
> >
> > What protects these two fields you are adding?
>
> The mutex in `struct uvc_video`. The lock in video_device is set to it in
> `uvc_register_video()` in f_uvc.c.
>
> >
> > > };
> > > #define to_uvc_file_handle(handle) \
> > > diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
> > > index 67922b1355e6..aee4888e17b1 100644
> > > --- a/drivers/usb/gadget/function/uvc_v4l2.c
> > > +++ b/drivers/usb/gadget/function/uvc_v4l2.c
> > > @@ -228,17 +228,57 @@ static int
> > > uvc_v4l2_subscribe_event(struct v4l2_fh *fh,
> > > const struct v4l2_event_subscription *sub)
> > > {
> > > + struct uvc_device *uvc = video_get_drvdata(fh->vdev);
> > > + struct uvc_file_handle *handle = to_uvc_file_handle(fh);
> > > + int ret;
> > > +
> > > if (sub->type < UVC_EVENT_FIRST || sub->type > UVC_EVENT_LAST)
> > > return -EINVAL;
> > > - return v4l2_event_subscribe(fh, sub, 2, NULL);
> > > + if ((sub->type == UVC_EVENT_SETUP) && (uvc->connections >= 1))
> > > + return -EBUSY;
> >
> > Are you sure you can't handle more than one connection?
> >
> > If so, why is it an integer and not just a boolean?
>
> It is possible to handle more than one subscription but I can't think of a
> scenario where this would make sense.
> For the reason that it is basically possible I decided for integer.
If it is not possible, just make it a bool so that we all can instantly
see that this is the case. If it needs to be changed in the future,
make that change then.
thanks,
greg k-h
