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

From: Gao feng <[email-masked]>
Date: Fri, 25 May 2012 14:02:37 +0800

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.

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