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From: Thomas Huth <thuth@redhat.com>
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Date: Mon, 22 Feb 2016 08:56:59 +0100
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Subject: Re: [Qemu-devel] [PATCHv7 4/9] slirp: Factorizing tcpiphdr
 structure with an union
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To: Samuel Thibault <samuel.thibault@gnu.org>
Cc: zhanghailiang <zhang.zhanghailiang@huawei.com>, Li Zhijian <lizhijian@cn.fujitsu.com>, Stefan Hajnoczi <stefanha@gmail.com>, Jason Wang <jasowang@redhat.com>, Dave Gilbert <dgilbert@redhat.com>, Vasiliy Tolstov <v.tolstov@selfip.ru>, qemu-devel@nongnu.org, Gonglei <arei.gonglei@huawei.com>, Jan Kiszka <jan.kiszka@siemens.com>, Huangpeng <peter.huangpeng@huawei.com>, Guillaume Subiron <maethor@subiron.org>

On 22.02.2016 02:48, Samuel Thibault wrote:
> Hello,
>=20
> Thomas Huth, on Fri 19 Feb 2016 14:44:59 +0100, wrote:
>>> +	m->m_data -=3D sizeof(struct tcpiphdr) - (sizeof(struct ip)
>>> +	                                     + sizeof(struct tcphdr));
>>> +	m->m_len +=3D sizeof(struct tcpiphdr) - (sizeof(struct ip)
>>> +	                                    + sizeof(struct tcphdr));
>>
>> I'm somewhat having a hard time to understand the  "+ sizeof(struct
>> tcphdr))" here.
>>
>> In the tcp_output.c code, there is this:
>>
>> 	m->m_data +=3D sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
>> 	                                     - sizeof(struct ip);
>>
>> So with my limited point of view, I'd rather expect this here in
>> tcp_input.c:
>>
>> 	m->m_data -=3D sizeof(struct tcpiphdr) - (sizeof(struct ip)
>> 	                                     - sizeof(struct tcphdr));
>> i.e. "-" instead of "+" here ----------------^
>=20
> The parentheses and indentation were misleading actually, here is how i=
t
> should actually looks like:
>=20
>>> +	m->m_data -=3D sizeof(struct tcpiphdr) - ( sizeof(struct ip)
>>> +	                                         + sizeof(struct tcphdr));
>=20
> I've now dropped the parentheses, so it looks like the tcp_output.c cod=
e:
>=20
> 	m->m_data -=3D sizeof(struct tcpiphdr) - sizeof(struct ip)
> 	                                     - sizeof(struct tcphdr);

Ah, sorry, I indeed simply got confused because it was written in two
different ways :-/ ... would it maybe be applicable to use the
TCPIPHDR_DELTA macro here instead?

Apart from that, the patch looks ok to me.

 Thomas