linux-kernel - Re: try_module_get code understanding

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Message-ID:  <loom.20070927T061840-329@post.gmane.org>
Date:	Thu, 27 Sep 2007 06:26:15 +0000 (UTC)
From:	Shreyansh Jain <shreyansh.jain@...il.com>
To:	linux-kernel@...r.kernel.org
Subject:  Re: try_module_get code understanding

Thanks for you reply, please see inline.

Heiko Carstens <heiko.carstens <at> de.ibm.com> writes:
> 
[snip]
> > static inline int try_module_get(struct module *module){
> >   int ret = 1;   <--- error case when !module
> >     if (module) {
> >          unsigned int cpu = get_cpu();
> >          if (likely(module_is_live(module)))
> >                 local_inc(&module->ref[cpu].count);
> >          else
> >                 ret = 0;   <--- error case
> >          put_cpu();
> >   }
> >   return ret;   <----
> > }
> > ----
[snip]
 
> Somewhere in module.h you have:
> 
> #ifdef MODULE
> #define THIS_MODULE (&__this_module)
> #else  /* !MODULE */
> #define THIS_MODULE ((struct module *)0)
> #endif
> 
> So this just means, that THIS_MODULE is NULL for compiled in modules
> and therefore try_module_get(NULL) succeeds. It's not an error case.

Agreed.

Then what is return value if my module tries to 'get' a module which does not
exist (and is a module, not in-built)? . Is it '1' ?
Or am I imagining a hypothetical scenario which would not exist?

Thanks again for your fast response.
Shreyansh

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