linux-kernel - Re: [RFC] eventfd: add EFD

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Message-ID: <20200212102912.GA464050@stefanha-x1.localdomain>
Date:   Wed, 12 Feb 2020 10:29:12 +0000
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Avi Kivity <avi@...lladb.com>,
        Davide Libenzi <davidel@...ilserver.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC] eventfd: add EFD_AUTORESET flag

On Wed, Feb 12, 2020 at 09:31:32AM +0100, Paolo Bonzini wrote:
> On 29/01/20 18:20, Stefan Hajnoczi wrote:
> > +	/* Semaphore semantics don't make sense when autoreset is enabled */
> > +	if ((flags & EFD_SEMAPHORE) && (flags & EFD_AUTORESET))
> > +		return -EINVAL;
> > +
> 
> I think they do, you just want to subtract 1 instead of setting the
> count to 0.  This way, writing 1 would be the post operation on the
> semaphore, while poll() would be the wait operation.

True!  Then EFD_AUTORESET is not a fitting name.  EFD_AUTOREAD or
EFD_POLL_READS?

Stefan

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