[systemd-devel] WebUSB

[Oliver Neukum]

On Tue, 2017-01-10 at 19:55 +0100, Lars Knudsen wrote



>         And we're quite happy to keep blacklisting specific VID/PID
>         combos we
>         know are not modems. Another possible solution is to greylist
>         devices
>         that happen to have webusb descriptors, such that they won't
>         get auto-
>         probed, but could be probed on-demand via D-Bus.  But I'd
>         rather that
>         happen via udev rules than MM trying to walk USB device
>         attributes and
>         parsing webusb descriptors.

> 
> If greylisting prevents auto-probing, I think it would be very
> valuable for devices with a WebUSB header because those will in most
> cases (as I see them used) be industrial things (like my current
> medical company employer) or IoT devices.  And waiting ~16 seconds for
> a fallback to USB Serial where WebUSB is not available (or for other
> reasons not chosen), can be a real pain.
> 
> 
> I agree that a solid udev rule would be a good way forward (I'll look
> into greylisting and see if I can come up with something that covers)
> and maybe this could also be the place to do the user space access (or
> not - I'll try to come back with something.

I am afraid this would not work. Or rather it would work once.
But as soon as the driver is already loaded, it will bind and
we have a beautiful race condition, which the kernel will almost
certainly win.
> 
And if we happen to look at a storage device we may see an unclean
removal if you kick the kernel off a device. I am afraid if you
really want to go to triggered probing, you need a sysctl for that.

	Regards
		Oliver