linux-kernel - Re: How to tell whether a struct file is held by a process?

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Date:	Fri, 22 May 2009 15:38:08 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Pantelis Koukousoulas <pktoss@...il.com>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: How to tell whether a struct file is held by a process?

Am Freitag, 22. Mai 2009 15:30:20 schrieb Pantelis Koukousoulas:
> The only problem I find with leaving mutual exclusion 100% to userspace and
> burdening the kernel only with the decision of whether a port should be
> handled by kernel or userspace is this:
>
> Suppose a device needs a reset as part of its init sequence (a whole lot
> of them do, this is not purely hypothetical). Then a different process may
> get to operate the device before and after the reset and hilarity may
> result from that.

If you leave the locking against user space to user space this can happen
any time, not just due to a reset. What is so special about reset? You just
need a user space locking scheme operating on port numbers, not device
addresses.

	Regards
		Oliver

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