From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:39882)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1YIbF6-0007j6-5q
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 06:02:08 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1YIbF2-0004JP-0m
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 06:02:04 -0500
Received: from mx1.redhat.com ([209.132.183.28]:42729)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1YIbF1-0004IQ-QI
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 06:01:59 -0500
Message-ID: <54D0AA9D.7040404@redhat.com>
Date: Tue, 03 Feb 2015 12:01:49 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <54CB3BB4.80406@cn.fujitsu.com>
	<20150130133955.GB24537@noname.redhat.com>
	<54CED08C.2080501@cn.fujitsu.com>
	<20150203092153.GA4488@noname.redhat.com>
In-Reply-To: <20150203092153.GA4488@noname.redhat.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 8bit
Subject: Re: [Qemu-devel] [PATCH] quorum: don't share qiov
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>, Wen Congyang <wency@cn.fujitsu.com>
Cc: qemu-devl <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>



On 03/02/2015 10:22, Kevin Wolf wrote:
> Paolo, I think it's rather surprising that iov_send_recv() modifies its
> iov. The modification is undone at the end, so you seem to have
> considered that a caller might be reusing it after and you can't "use it
> up", but we still get problems with concurrent accesses.

Yes, I wasn't thinking of concurrent accesses indeed.  But I wasn't the
author of iov_send_recv(), I just took it from sheepdog. :)

> Was it an intentional design decision that iov_send_recv() is the sole
> owner of the iov and the caller must duplicate it if it's used elsewhere
> concurrently?
>
> Otherwise I would suggest to fix iov_send_recv(), and possibly try and
> make all the qiov/iov arguments in the block layer const.

I agree.  However, it's not a small change.  I think Wen's patch is okay
with a FIXME comment added.

Paolo