From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove
Date: Thu, 21 Jan 2010 19:50:15 +0200
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Cc: Avi Kivity <avi@redhat.com>, mtosatti@redhat.com,
	kvm@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To: Davide Libenzi <davidel@xmailserver.org>
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On Thu, Jan 21, 2010 at 09:50:34AM -0800, Davide Libenzi wrote:
> On Thu, 21 Jan 2010, Avi Kivity wrote:
> 
> > On 01/21/2010 07:32 PM, Michael S. Tsirkin wrote:
> > > 
> > > > Can't you read from the file?
> > > >      
> > > IMO no, the read could block.
> > >    
> > 
> > But you're in process context.  An eventfd never blocks.
> 
> Can you control the eventfd flags? Because if yes, O_NONBLOCK will never 
> block.
> 

Userspace can but kvm can't.

> 
> - Davide
>