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Date: Mon, 24 Aug 2009 21:31:47 +0300
From: Avi Kivity <avi@redhat.com>
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To: Davide Libenzi <davidel@xmailserver.org>
CC: "Michael S. Tsirkin" <mst@redhat.com>, gleb@redhat.com,
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Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag
References: <20090820155655.GA8764@redhat.com> <alpine.DEB.2.00.0908200916300.14844@makko.or.mcafeemobile.com> <4A8D8A28.2050004@redhat.com> <20090820175540.GA9232@redhat.com> <4A8D90BB.2030506@redhat.com> <20090820182847.GB9282@redhat.com> <4A913DA9.1020403@redhat.com> <20090823133620.GA12841@redhat.com> <4A9146E3.2090007@redhat.com> <20090823143021.GA27495@redhat.com> <alpine.DEB.2.00.0908241114501.7951@makko.or.mcafeemobile.com>
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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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.