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

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Date:	Wed, 26 Aug 2009 22:42:05 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Davide Libenzi <davidel@...ilserver.org>
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 08/26/2009 10:13 PM, Davide Libenzi wrote:
> Ok, so why not using the eventfd counter as state?
> On the device side:
>
> void write_state(int sfd, int state) {
> 	u64 cnt;
>
> 	/* Clear the current state, sfd is in non-blocking mode */
> 	read(sfd,&cnt, sizeof(cnt));
> 	/* Writes new state */
> 	cnt = 1 + !!state;
> 	write(sfd,&cnt, sizeof(cnt));
> }
>
>
> On the hypervisor side:
>
> int read_state(int sfd) {
> 	u64 cnt;
>
> 	read(sfd,&cnt, sizeof(cnt));
> 	return state - 1;
> }
>
>    

Hadn't though of read+write as set.  While the 1+ is a little ugly, it's 
workable.

I see no kernel equivalent to read(), but that's easily done.

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

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