linux-kernel - Re: [patch] eventfd - revised interface and cleanups

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Message-ID: <alpine.DEB.1.10.0906231049520.17001@makko.or.mcafeemobile.com>
Date:	Tue, 23 Jun 2009 10:51:28 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, avi@...hat.com,
	kvm@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [patch] eventfd - revised interface and cleanups

On Tue, 23 Jun 2009, Gregory Haskins wrote:

> I think the lack of a way to got from a file* to a ctx* (or back) might
> be a problem.  I am not an expert, but if I understood the gist of what
> Al Viro (cc'd) was saying early on, an fd can change meaning out from
> under you without warning.
> 
> With the code the way it is now, I would need to call both
> eventfd_fget() and eventfd_ctx_fdget() to fully acquire state (unless I
> am missing something).  I would think that is a race and I am not
> guaranteed to get the same object.  Can we also have a way to convert
> one reference to the other?  I am thinking
> 
> struct eventfd_ctx *eventfd_ctx_fget(struct file *)
> 
> (or similar) would be sufficient.

You're right. That function was available in the previous patch, but then 
I dropped it because I thought the eventfd code could be simplified. But 
yes, it's needed.



- Davide


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