strange code in linux kernel

strange code in linux kernel

[Rajat Jain]

Hi List,

I found that there are some weird looking instances in kernel where a
function has been DEFINED (as opposite to DECLARED) using and "extern"
keyword. For e.g., the following code in arch/alpha/include/asm/io.h:

extern inline void __iomem *generic_ioportmap(unsigned long a)
{
        return alpha_mv.mv_ioportmap(a);
}

Using a definition along with extern does not make any sense to me.
Can some one please enlighten what is its use / purpose?

Thanks,

Rajat Jain

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Re: strange code in linux kernel

[Michal Nazarewicz]

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Rajat Jain <rajat.noida.india@gmail.com> writes:
> I found that there are some weird looking instances in kernel where a
> function has been DEFINED (as opposite to DECLARED) using and "extern"
> keyword. For e.g., the following code in arch/alpha/include/asm/io.h:
>
> extern inline void __iomem *generic_ioportmap(unsigned long a)
> {
>         return alpha_mv.mv_ioportmap(a);
> }
>
> Using a definition along with extern does not make any sense to me.
> Can some one please enlighten what is its use / purpose?

Note that at the same time an "inline" keyword has been used.  You might
want to refer to GCC's documentation in particular
<http://gcc.gnu.org/onlinedocs/gcc/Inline.html> for more information.
Google also pointed to this site
<http://www.greenend.org.uk/rjk/2003/03/inline.html> which also might
have some insight.

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