From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close() Date: Wed, 3 Jun 2009 09:39:56 +0300 Message-ID: <20090603063956.GA8134@redhat.com> References: <20090602151135.29746.91320.stgit@dev.haskins.net> <20090602160434.GA6827@redhat.com> <4A254FD7.5090302@novell.com> <20090602162021.GB6827@redhat.com> <4A255484.6060401@novell.com> <20090602165949.GD6827@redhat.com> <4A256431.2080101@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, avi@redhat.com, davidel@xmailserver.org, paulmck@linux.vnet.ibm.com To: Gregory Haskins Return-path: Received: from mx2.redhat.com ([66.187.237.31]:58511 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbZFCGkw (ORCPT ); Wed, 3 Jun 2009 02:40:52 -0400 Content-Disposition: inline In-Reply-To: <4A256431.2080101@novell.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Jun 02, 2009 at 01:41:05PM -0400, Gregory Haskins wrote: > > And having close not clean up the state unless you do an ioctl first is > > very messy IMO - I don't think you'll find any such examples in kernel. > > > > > > I agree, and that is why I am advocating this POLLHUP solution. It was > only this other way to begin with because the technology didn't exist > until Davide showed me the light. > > Problem with your request is that I already looked into what is > essentially a bi-directional reference problem (for a different reason) > when I started the POLLHUP series. Its messy to do this in a way that > doesn't negatively impact the fast path (introducing locking, etc) or > make my head explode making sure it doesn't race. Afaict, we would need > to solve this problem to do what you are proposing (patches welcome). > > If this hybrid decoupled-deassign + unified-close is indeed an important > feature set, I suggest that we still consider this POLLHUP series for > inclusion, and then someone can re-introduce DEASSIGN support in the > future as a CAP bit extension. That way we at least get the desirable > close() properties that we both seem in favor of, and get this advanced > use case when we need it (and can figure out the locking design). > FWIW, I took a look and yes, it is non-trivial. I concur, we can always add the deassign ioctl later. -- MST