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

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Message-ID: <1295ed070905220652q55c65e8bx992940b626eecda3@mail.gmail.com>
Date:	Fri, 22 May 2009 16:52:23 +0300
From:	Pantelis Koukousoulas <pktoss@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
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?

On Fri, May 22, 2009 at 4:43 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>> 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.
>
> Thats surely up to you to get your lock file usage right. The kernel
> isn't there to play mother to crap programming.

Who is "me" in this case? Assuming that those writing the userspace programs
are cooperative though, I agree. We can declare that whatever program does not
play by the (userspace locking) rules is crap and either fix it (if open source)
or refuse to install it / complain (if closed source).

>
>> So, if there is a clean / acceptable way to handle the reset issue in userspace
>
> Firstly can you explain *why* you think there is a problem ?
>

I admit this could be a bias from the way I imagined the whole thing
to work before
this discussion. I think I can see how a userspace locking scheme based on port
numbers could avoid also the reset problem.

Thanks,
Pantelis
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