linux-kernel - Re: [KVM PATCH 2/3] eventfd: add a notifier mechanism

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Message-ID: <alpine.DEB.1.10.0904231942000.18603@makko.or.mcafeemobile.com>
Date:	Thu, 23 Apr 2009 19:43:59 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com
Subject: Re: [KVM PATCH 2/3] eventfd: add a notifier mechanism

On Thu, 23 Apr 2009, Gregory Haskins wrote:

> > Take a look at init_waitqueue_func_entry(), in particula at that "func" 
> > parameter. Then look at how __wake_up_common() does its thing.
> > You don't need to be "waiting" for our wakeup system to work. Callbacks 
> > works just fine, otherwise things like epoll could not work at all.
> >   
> 
> Yeah, I was looking at that this afternoon after you mentioned it.  That
> makes sense.
> 
> As of right now the wqh is embedded in the eventfd, accessible only by
> the .read() vtable entry.  In order to do this as you suggest, I imagine
> I need to slightly modify the eventfd interface to allow waiters other
> than the embedded readers to join the wait-queue.  How would you like to
> see that interface look?

Actually, you need no changes in eventfd, since you can use its poll() 
directly, by dropping a callback entry.
Take a look at how epoll does it in ep_insert()...


- Davide


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