From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58090) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d5rkA-0000Xb-BR for qemu-devel@nongnu.org; Wed, 03 May 2017 06:42:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d5rk5-0001LY-Fb for qemu-devel@nongnu.org; Wed, 03 May 2017 06:42:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45696) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1d5rk5-0001LI-8p for qemu-devel@nongnu.org; Wed, 03 May 2017 06:42:45 -0400 References: <1493372840-24551-1-git-send-email-zhangchen.fnst@cn.fujitsu.com> <1493372840-24551-6-git-send-email-zhangchen.fnst@cn.fujitsu.com> <7bde3681-280c-764a-71df-f4a1cc4b7011@redhat.com> <4cc14276-55bc-2981-cbdd-4d66ae6be59e@cn.fujitsu.com> From: Jason Wang Message-ID: Date: Wed, 3 May 2017 18:42:36 +0800 MIME-Version: 1.0 In-Reply-To: <4cc14276-55bc-2981-cbdd-4d66ae6be59e@cn.fujitsu.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH V3 05/10] net/net.c: Add vnet header length to SocketReadState List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Zhang Chen , qemu devel Cc: zhanghailiang , Li Zhijian , weifuqiang , "eddie . dong" , bian naimeng On 2017=E5=B9=B405=E6=9C=8803=E6=97=A5 11:43, Zhang Chen wrote: > > > On 05/02/2017 12:53 PM, Jason Wang wrote: >> >> >> On 2017=E5=B9=B404=E6=9C=8828=E6=97=A5 17:47, Zhang Chen wrote: >>> Address Jason Wang's comments add vnet header length to=20 >>> SocketReadState. >> >> Instead of saying this, you can add "Suggested-by: Jason Wang=20 >> " above your sign-off. > > OK. > >> >>> So we change net_fill_rstate() to read >>> struct {int size; int vnet_hdr_len; const uint8_t buf[];}. >> >> This makes me thinking about the backward compatibility. I think we'd=20 >> better try to keep it as much as possible. E.g how about pack=20 >> vnet_hdr_len into higher bits of size? >> > > Do you means split uint32_t size to uint16_t size and uint16_t=20 > vnet_hdr_len ? > If yes, we also can't keep compatibility with old version. > Old code send a uint32_t size, we read it as uint16_t size is always=20 > wrong. > > Thanks > Zhang Chen Consider it's unlikely to send or receive packet >=3D 64K, we can reuse=20 higher bits (e.g highest 8 bits). Then we can still read uint32_t and=20 then check its highest 8 bits. If it was zero, we know vnet header is=20 zero, if not it could be read as vnet header length. Thanks