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Re: [Qemu-devel] [PATCHv7 4/9] slirp: Factorizing tcpiphdr structure wit
From: |
Thomas Huth |
Subject: |
Re: [Qemu-devel] [PATCHv7 4/9] slirp: Factorizing tcpiphdr structure with an union |
Date: |
Wed, 10 Feb 2016 11:08:55 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
On 10.02.2016 10:28, Samuel Thibault wrote:
> That one is tricky, yes :)
>
> Thomas Huth, on Wed 10 Feb 2016 09:05:32 +0100, wrote:
>>> -#define SLIRP_MSIZE (IF_MTU + IF_MAXLINKHDR + offsetof(struct mbuf, m_dat)
>>> + 6)
>>> +#define SLIRP_MSIZE\
>>> + (offsetof(struct mbuf, m_dat) + IF_MAXLINKHDR + TCPIPHDR_DELTA +
>>> IF_MTU)
>>
>> I'm somehow having a hard time to understand why TCPIPHDR_DELTA is used
>> here. As far as I understand, TCPIPHDR_DELTA is the difference between
>> the size of struct tcpiphdr and the size of the IPv4 + TCP header. But
>> if it's just the difference, where does the base size of the headers
>> come from in this define, since the headers are stored in the mbuf, too,
>> aren't they? ... I've got the feeling that I miss something here, could
>> you enlighten me?
>
> TCP/IP headers are within IF_MTU.
Ah, of course, that makes sense, thanks! ... so in the old definition of
SLIRP_MSIZE, the TCP/IP headers were counted twice, I guess? Anyway, the
definition looks fine to me now.
Thomas
[Qemu-devel] [PATCHv7 8/9] slirp: Adding IPv6 address for DNS relay, Samuel Thibault, 2016/02/08
[Qemu-devel] [PATCHv7 7/9] slirp: Handle IPv6 in TCP functions, Samuel Thibault, 2016/02/08
[Qemu-devel] [PATCHv7 5/9] slirp: Generalizing and neutralizing various TCP functions before adding IPv6 stuff, Samuel Thibault, 2016/02/08
[Qemu-devel] [PATCHv7 9/9] qapi-schema, qemu-options & slirp: Adding Qemu options for IPv6 addresses, Samuel Thibault, 2016/02/08