linux-kernel - Re: usbfs, claiming entire usb devices

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Date:	Fri, 8 May 2009 10:06:27 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kay Sievers <kay.sievers@...y.org>
cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	Pantelis Koukousoulas <pktoss@...il.com>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: usbfs, claiming entire usb devices

On Fri, 8 May 2009, Kay Sievers wrote:

> You mentioned earlier, that you would need to match the holder of the
> "lock" and the one that accesses the device?

Yes.  That is, a process shouldn't be allowed to access a locked device 
unless that process is the lock holder.

> Wouldn't it be sufficient already, if you can take a "lock" at the
> specific port, that prevents the kernel to access the device when it
> shows up?

I don't know how the people requesting this feature would feel about
that.  They seem to want to lock out other processes as well as locking
out the kernel.

> You thought of supporting a number of different users, with different
> uids, or would that be a root-only action?

A typical use case would be somebody running an emulator like QEMU.  In 
theory there could be multiple QEMU processes running concurrently, 
each owning a different set of ports.  The uids might be different or 
they might all be the same.

Setting the lock permissions would be up to userspace.

Alan Stern

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