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Date: Wed, 26 Aug 2009 22:42:05 +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,
       kvm@vger.kernel.org,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag
References: <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> <20090824214900.GA9899@redhat.com> <alpine.DEB.2.00.0908241508440.7951@makko.or.mcafeemobile.com> <20090825072229.GA10608@redhat.com> <alpine.DEB.2.00.0908251456230.18518@makko.or.mcafeemobile.com> <20090826102908.GA21523@redhat.com> <alpine.DEB.2.00.0908261040100.7780@makko.or.mcafeemobile.com> <4A9585EC.2030505@redhat.com> <alpine.DEB.2.00.0908261201570.7780@makko.or.mcafeemobile.com>
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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.