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

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Message-ID: <20090823143021.GA27495@redhat.com>
Date:	Sun, 23 Aug 2009 17:30:22 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>, 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 Sun, Aug 23, 2009 at 04:40:51PM +0300, Avi Kivity wrote:
> On 08/23/2009 04:36 PM, Michael S. Tsirkin wrote:
>> More important here is realization that eventfd is a mutex/semaphore
>> implementation, not a generic event reporting interface as we are trying
>> to use it.
>>    
>
> Well it is a generic event reporting interface (for example, aio uses it).

Davide, I think it's a valid point.  For example, what read on eventfd
does (zero a counter and return) is not like any semaphore I saw.

Look at eventfd as pipe replacement: for wake-up between processes, it
works well. But what if we want to pass around some kind of key as well?
pipe lets you pass single-byte values atomically. This flag allows us to
use 8 byte values as keys.

> -- 
> error compiling committee.c: too many arguments to function
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