From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:53559)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1ZUwKc-0001se-Ck
	for qemu-devel@nongnu.org; Thu, 27 Aug 2015 08:31:06 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1ZUwKZ-0005NS-7f
	for qemu-devel@nongnu.org; Thu, 27 Aug 2015 08:31:02 -0400
Received: from mx1.redhat.com ([209.132.183.28]:43434)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1ZUwKZ-0005Mv-2W
	for qemu-devel@nongnu.org; Thu, 27 Aug 2015 08:30:59 -0400
Date: Thu, 27 Aug 2015 15:30:55 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20150827152902-mutt-send-email-mst@redhat.com>
References: <55DE970B.6040807@redhat.com>
	<CAFEAcA_JQdnmjdhsh_+eBrMuCa31jpEXCCOdfTqDFiKv4y6Xmg@mail.gmail.com>
	<20150827135126-mutt-send-email-mst@redhat.com>
	<CAFEAcA-=sW5m3ryFhBU2gz9U5VEzu-rCZaU4g-c_SbPW1XujOg@mail.gmail.com>
	<20150827140715-mutt-send-email-mst@redhat.com>
	<CAFEAcA98H6QLyjL5TnLiZjENRZkJPRgtagvnaDcJ6ULgSNBzwA@mail.gmail.com>
	<20150827151601-mutt-send-email-mst@redhat.com>
	<CAFEAcA8MwmWvuPFd8R8UVNeBkJaP59v7gAB619=0AX7GZAKEAA@mail.gmail.com>
	<20150827152348-mutt-send-email-mst@redhat.com>
	<CAFEAcA_aEHs2c_rEoG55Hx9NX7bGAj0TtGVXZit07NKstvtDrw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAFEAcA_aEHs2c_rEoG55Hx9NX7bGAj0TtGVXZit07NKstvtDrw@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH 1/2] memory: allow zero size for
 adjust_endianness()
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: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jason Wang <jasowang@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Greg Kurz <gkurz@linux.vnet.ibm.com>

On Thu, Aug 27, 2015 at 01:27:54PM +0100, Peter Maydell wrote:
> On 27 August 2015 at 13:25, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Thu, Aug 27, 2015 at 01:20:52PM +0100, Peter Maydell wrote:
> >> On 27 August 2015 at 13:17, Michael S. Tsirkin <mst@redhat.com> wrote:
> >> > Basically the point is that ABI is extended to make
> >> > ioeventfd with len = 0 mean "any length".
> >> > 0 is thus not meaningless anymore.
> >>
> >> But how can you do adjustment for incorrect endianness
> >> if you don't know the size of the data that you're
> >> trying to work with? That's why this switch insists
> >> that the size is 1, 2, 4 or 8.
> 
> > For kvm at least, "any length" implies "any data".
> > So data is eventually discarded, we don't really need
> > to adjust it for endian-ness.
> 
> I'm still confused. If you have data it needs to be
> adjusted. If we're not actually doing anything with
> the data why are we calling this function in the first
> place?
> 
> -- PMM

I guess you could skip calls to adjust_endianness when len == 0,
that should work just as well.

-- 
MST