Look for 'forward declaration' of variables in C.
You are telling the compiler that "I am declaring such a structure. Understand it when you encounter it" .
- Durga
From: Sukanto Ghosh <sukanto.cse.iitb@xxxxxxxxx>
To: Nelson Castillo <nelsoneci@xxxxxxxxx>; Pei Lin <telent997@xxxxxxxxx>
Cc: kernelnewbies <kernelnewbies@xxxxxxxxxxxx>
Sent: Thursday, March 12, 2009 3:06:46 PM
Subject: Re: structure definition in a .c file rather than .h file
On Thu, Mar 12, 2009 at 11:58 AM, Nelson Castillo <nelsoneci@xxxxxxxxx> wrote:
> On Thu, Mar 12, 2009 at 2:06 PM, Sukanto Ghosh
> <sukanto.cse.iitb@xxxxxxxxx> wrote:
>> Hi,
>>
>> The complete definition of structure cfs_rq is in a .c file
>> (kernel/sched.c). In the head linux/sched.h it has been declared as
>> "struct cfs_rq;"
>> What is the purpose of doing so ?
>
> With this declaration in linux/sched.h you can make pointers of the
> structure anywhere. All pointers have the same size thus it just
> doesn't matter if you don't know the details of the structure.
>
> The idea of not exposing the structure is just encapsulation. It means
> you shouldn't be touching those fields outside kernel/sched.c unless
> you use one of the provided API functions to do so (if any).
>
exactly, and yet the fields have been used in kernel/sched_fair.c
.... this is what confuses me
--
Regards,
Sukanto Ghosh
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