linux-kernel - Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

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Message-ID: <20100121175014.GI16707@redhat.com>
Date:	Thu, 21 Jan 2010 19:50:15 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Avi Kivity <avi@...hat.com>, mtosatti@...hat.com,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

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
> 
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