On Mon, Apr 25, 2022 at 03:23:15PM +0200, Bastien Nocera wrote:
> There is a need for userspace applications to open USB devices directly,
> for all the USB devices without a kernel-level class driver, and
> implemented in user-space.
>
> End-user access is usually handled by the uaccess tag in systemd,
> shipping application-specific udev rules that implement this without too
> much care for sandboxed applications, or overall security, or just sudo.
>
> A better approach is what we already have for evdev devices: give the
> application a file descriptor and revoke it when it may no longer access
> that device.
Who is going to use this "better" approach? Is there support in libusb
for it? Who talks raw usbfs other than libusb these days?
>
> This patch is the USB equivalent to the EVIOCREVOKE ioctl, see
> commit c7dc65737c9a607d3e6f8478659876074ad129b8 for full details.
c7dc65737c9a ("Input: evdev - add EVIOCREVOKE ioctl") is how I thought
we were supposed to write out commits in changelogs these days :)
>
> Note that this variant needs to do a few things that the evdev revoke
> doesn't need to handle, particular:
> - cancelling pending async transfers
> - making sure to release claimed interfaces on revoke so they can be
> opened by another process/user, as USB interfaces require being
> exclusively claimed to be used.
I love the idea of a real revoke() someday, but can't you just do the
"unbind/bind" hack instead if you really want to do this? Who wants to
pass usbfs file descriptors around these days?
thanks,
greg k-h
