Re: [RFC v1] USB: core: add USBDEVFS_REVOKE ioctl

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Apr 26, 2022 at 09:14:04AM +0200, Oliver Neukum wrote:
> 
> 
> On 26.04.22 04:27, Peter Hutterer wrote:
> >
> > chiming in here: the hidraw ioctl is independent (as already mentioned)
> > but it's basically the same approach and/or intent. The hidraw revoke ioctl is
> > "the evdev revoke, but for hidraw", this one is "the evdev revoke, but for
> > usb". Not very creative, but at least we can point to prior art and say "this
> > seems to be useful" :)
> >
> > The primary focus of all this are joystick devices (unless I missed some other
> > grand plans Bastien had that I'm not aware of), that should put things in
> > context a bit. 
> >
> Hi,
> 
> taking the advantages as a given, I must still ask, why this, if it is
> so useful,
> should be implemented for each subsystem separately. I cannot help but
> say that this should go into the VFS.

Yes, but, it's not so simple.  Many people have asked for revoke() to be
added as a syscall like is in the BSDs, but the BSDs only allow that for
a very small subset of file descriptor types, and doing it in a generic
fashion seems very difficult (I tried a few years ago and gave up, but
my knowledge of the vfs layer is minimal.)

However doing it as a per-device/subsystem ioctl also seems crazy so
perhaps we do just implement it at the vfs layer and let whatever
device/filesystem type that wants to support it, hook up to it.  That
would make it much easier over time to implement in a way that works for
everyone and is easier to understand from userspace.

thanks,

greg k-h