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

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Message-ID: <Pine.LNX.4.44L0.0905221522560.3006-100000@iolanthe.rowland.org>
Date:	Fri, 22 May 2009 15:31:18 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kay Sievers <kay.sievers@...y.org>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Kyle Moffett <kyle@...fetthome.net>,
	Pantelis Koukousoulas <pktoss@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: How to tell whether a struct file is held by a process?

On Fri, 22 May 2009, Kay Sievers wrote:

> On Fri, May 22, 2009 at 17:54, Alan Stern <stern@...land.harvard.edu> wrote:
> 
> >> Would releasing the "lock" trigger a kernel-driver-binding call?
> >
> > No. Â If the lock owner wants to bind kernel drivers, it can use the
> > existing API in libusb after releasing the lock. Â This might cause
> > problems if the owning process terminates abnormally, but I think we
> > can live with that.
> >
> >> The lock will always lock all devices of a specific hub?
> >
> > The idea is that there will be one lock file per port. Â So for example,
> > a hub device with four ports might contain inside its sysfs device
> > directory: ports/1, ..., ports/4.
> 
> Sounds both good to me.

Come to think of it, putting the lock files in sysfs isn't such a good 
idea.  The core will need to know whether the files are open, so we'll 
have to have our own file_operations structure for them.

Which means the best place to put the lock files is probably somewhere 
in /dev.  Can this be made to work by generating appropriate uevents, 
with the default udev rules?

Alan Stern

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