From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:51179)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TDzMe-0001fB-1T
	for qemu-devel@nongnu.org; Tue, 18 Sep 2012 11:05:33 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TDzMZ-0001UF-Lm
	for qemu-devel@nongnu.org; Tue, 18 Sep 2012 11:05:27 -0400
Received: from mx1.redhat.com ([209.132.183.28]:35785)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TDzMZ-0001T5-Dq
	for qemu-devel@nongnu.org; Tue, 18 Sep 2012 11:05:23 -0400
Received: from int-mx02.intmail.prod.int.phx2.redhat.com
	(int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12])
	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q8IF5MeZ014542
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK)
	for <qemu-devel@nongnu.org>; Tue, 18 Sep 2012 11:05:22 -0400
Message-ID: <50588DB0.1000207@redhat.com>
Date: Tue, 18 Sep 2012 17:05:20 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <1347968442-8860-1-git-send-email-kwolf@redhat.com>
	<1347968442-8860-16-git-send-email-kwolf@redhat.com>
	<505888CC.8070207@redhat.com> <50588D22.6080703@redhat.com>
In-Reply-To: <50588D22.6080703@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [RFC PATCH 15/16] qcow2: Cancel COW when
	overwritten
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org

Il 18/09/2012 17:02, Kevin Wolf ha scritto:
>>> >> +    qemu_co_mutex_unlock(&s->lock);
>>> >> +    qemu_co_rwlock_wrlock(&m->l2_writeback_lock);
>> > 
>> > Can anybody else take the lock as reader again at this point?  If not, I
>> > wonder if this is more clear if you write it as a CoQueue.
> This isn't "let one writer complete, then wake up n readers" (which
> would indeed be represented more naturally as CoQueue), but rather "let
> n readers complete, then wake up one writer".

So would it be representable as a list of children (matching the parent
pointer) and then unlocking is

  remove self from children list
  if the children list is empty, wake parent->co

?

Paolo