linux-kernel - Re: [PATCH 0/2] eventfd: new EFD

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Message-ID: <alpine.DEB.2.00.0908241503150.7951@makko.or.mcafeemobile.com>
Date:	Mon, 24 Aug 2009 15:08:16 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Avi Kivity <avi@...hat.com>
cc:	"Michael S. Tsirkin" <mst@...hat.com>, gleb@...hat.com,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag

On Mon, 24 Aug 2009, Avi Kivity wrote:

> On 08/24/2009 09:25 PM, Davide Libenzi wrote:
> > Indeed, the default eventfd behaviour is like, well, an event. Signaling
> > (kernel side) or writing (userspace side), signals the event.
> > Waiting (reading) it, will reset the event.
> > If you use EFD_SEMAPHORE, you get a semaphore-like behavior.
> > Events and sempahores are two widely known and used abstractions.
> > The EFD_STATE proposed one, well, no. Not at all.
> >    
> 
> There are libraries that provide notifications (or fire watches) when some
> value changes.  They're much less frequently used than events or semaphores,
> though.

There are userspace libraries that do almost everything, but you hardly 
see things like pthread_(EFD_STATE-like)_create() or similar system 
interfaces based on such abstraction.
Is that really difficult to understand where I'm standing, leaving the KVM 
hat off for a moment?



- Davide


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