Re: [PATCH v3] usb: gadget: uvc: fix multiple opens

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Nov 10, 2020 at 03:30:15PM +0100, thomas.haemmerle@wolfvision.net wrote:
> From: Thomas Haemmerle <thomas.haemmerle@wolfvision.net>
> 
> 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 the
> UVC application potentially is streaming.
> 
> Move activation of UVC function to subscription on UVC_EVENT_SETUP
> because there we can guarantee for a userspace application utilizing UVC.
> Block subscription on UVC_EVENT_SETUP while another application already
> is subscribed to it, indicated by `bool func_connected` in
> `struct uvc_device`.
> Extend the `struct uvc_file_handle` with member `bool is_uvc_app_handle`
> to tag it as the handle used by the userspace UVC application.
> 
> With this a process is able to check capabilities of the v4l2 device
> without deactivating the function for the actual UVC application.
> 
> Signed-off-by: Thomas Haemmerle <thomas.haemmerle@wolfvision.net>
> ---
> v3:
>  - replace `unsigned int connections` with `bool func_connected`
>  - rename `bool connected` to `bool is_uvc_app_handle`

Can you fix this up based on Hans's review?

thanks,

greg k-h