netfilter kernel modules question

netfilter kernel modules question

[Tobias Koeck]

I have two netfilter kernel modules (xt_RQS.c, xt_RQD.c, both include 
a header file with a data structure in it).

Does both kernel modules use the same datastructures or do they use 
seperate ones (in normal C programming I know that but I'm not sure 
about the kernel scopes).

If I want to use one datastructure how can I do that (export? - 
concurrency issues left aside)?

Greetings and thanks

Re: netfilter kernel modules question

[Jan Engelhardt]

On Monday 2009-12-14 16:20, Tobias Koeck wrote:

> I have two netfilter kernel modules (xt_RQS.c, xt_RQD.c, both include a header
> file with a data structure in it).
>
> Does both kernel modules use the same datastructures or do they use seperate
> ones (in normal C programming I know that but I'm not sure about the kernel
> scopes).

You decide whether they do. This does not change just because you are in 
kernel space.



Jan

Re: netfilter kernel modules question

[Tobias Koeck]

On 12/14/2009 09:17 PM, Jan Engelhardt wrote:
> On Monday 2009-12-14 16:20, Tobias Koeck wrote:
>
>> I have two netfilter kernel modules (xt_RQS.c, xt_RQD.c, both include a header
>> file with a data structure in it).
>>
>> Does both kernel modules use the same datastructures or do they use seperate
>> ones (in normal C programming I know that but I'm not sure about the kernel
>> scopes).
>
> You decide whether they do. This does not change just because you are in
> kernel space.
Can you please give a short example how to to it?

Let's say you've got one data structure (int a) in the header file. 
How can you access it in both c-files? Do you have to export it?

Is there a deeper information how the kernel scope is structured?

Re: netfilter kernel modules question

[Jan Engelhardt]

On Monday 2009-12-14 21:28, Tobias Koeck wrote:
>>> I have two netfilter kernel modules (xt_RQS.c, xt_RQD.c, both include a
>>> header
>>> file with a data structure in it).
>>>
>>> Does both kernel modules use the same datastructures or do they use seperate
>>> ones (in normal C programming I know that but I'm not sure about the kernel
>>> scopes).
>>
>> You decide whether they do. This does not change just because you are in
>> kernel space.
>
> Can you please give a short example how to to it?
>
> Let's say you've got one data structure (int a) in the header file. How can you
> access it in both c-files? Do you have to export it?

You can argue what a data structure is or what it is not; a header
file should not include any definitions, only declarations. (And
perhaps static-inlines, but that's probably too expert for you at
this stage.) Various C-related forums or IRC channels can enlighten
you towards the reasoning for that.

Re: netfilter kernel modules question

[Tobias Koeck]

 >
 > You can argue what a data structure is or what it is not; a header
 > file should not include any definitions, only declarations. (And
 > perhaps static-inlines, but that's probably too expert for you at
 > this stage.) Various C-related forums or IRC channels can enlighten
 > you towards the reasoning for that.

'int a' is declaration (only used in a function it's a definition).

Does that mean if I define a (nonstatic) variable in a kernel module 
and it's accessible in the whole kernel?

Don't worry - last kernel newbie question from myself ;=).

Greetings
tk

Re: netfilter kernel modules question

[Jan Engelhardt]

On Monday 2009-12-14 21:48, Tobias Koeck wrote:
>>
>> You can argue what a data structure is or what it is not; a header
>> file should not include any definitions, only declarations. (And
>> perhaps static-inlines, but that's probably too expert for you at
>> this stage.) Various C-related forums or IRC channels can enlighten
>> you towards the reasoning for that.
>
> 'int a' is declaration (only used in a function it's a definition).

"int a" is always a definition. Inside a function it makes for an 
automatic variable, and outside a function it makes for one with static 
linkage.