Subject: Re: [PATCH 01/17] netfilter: add struct nf_proto_net for register l4proto sysctl

From: Gao feng <[email-masked]>
Date: Sat, 26 May 2012 10:28:33 +0800

于 2012年05月25日 14:02, Gao feng 写道:
> 于 2012年05月25日 10:54, Pablo Neira Ayuso 写道:
>> On Fri, May 25, 2012 at 09:05:34AM +0800, Gao feng wrote:
>>> 于 2012年05月24日 22:38, Pablo Neira Ayuso 写道:
>>>> On Thu, May 24, 2012 at 06:54:42PM +0800, Gao feng wrote:
>>>> [...]
>>>>>>>> I don't see why we need this new field.
>>>>>>>>
>>>>>>>> It seems to be set to 1 in each structure that has set:
>>>>>>>>
>>>>>>>> .ctl_compat_table
>>>>>>>>
>>>>>>>> to non-NULL. So, it's redundant.
>>>>>>>>
>>>>>>>> Moreover, you already know from the protocol tracker itself if you
>>>>>>>> have to allocate the compat ctl table or not.
>>>>>>>>
>>>>>>>> In other words: You set compat to 1 for nf_conntrack_l4proto_generic.
>>>>>>>> Then, you pass that compat value to generic_init_net via ->inet_net
>>>>>>>> again, but this information (that determines if the compat has to be
>>>>>>>> done or not) is already in the scope of the protocol tracker.
>>>>>>>>
>>>>>>>
>>>>>>> because some protocols such l4proto_tcp6 and l4proto_tcp use the same init_net
>>>>>>> function. the l4proto_tcp6 doesn't need compat sysctl, so we should use this new
>>>>>>> field to identify if we should kmemdup compat_sysctl_table.
>>>>>>
>>>>>> Then, could you use two init_net functions? one for TCP for IPv4 and another
>>>>>> for TCP for IPv6?
>>>>>
>>>>> Of cause, if you prefer to impletment it in this way.
>>>>
>>>> If this removes the .compat field that you added, then use two
>>>> init_net functions, yes.
>>>
>>> Sorry I miss something.
>>>
>>> nf_ct_l4proto_unregister_sysctl also uses .compat to identify if we
>>> can unregister the compat sysctl.
>>>
>>> if we register l4proto_tcp and l4proto_tcp6 both. without .compat,
>>> when unregister l4proto_tcp6, the compat sysctl will be unregister too.
>>>
>>> So maybe we have to use .compat.
>>
>> Could you resolve this by checking pn->ctl_compat_header != NULL ?
> 
> pn->ctl_table_header and ctl_compat_header is shared by l4proto_tcp and l4proto_tcp6.
> if we both register l4proto_tcp and l4proto_tcp6, when unregister l4proto_tcp6
> pn->ctl_compat_header must not be NULL.
> 

Maybe we can resolve this by  nf_conntrack_l4proto.l3proto == AF_INET &&  pn->ctl_compat_header != NULL
Because compat sysctl is registered by AF_INET's proto only.

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