On Tue, 2018-11-06 at 09:20 -0800, Alexander Duyck wrote:
> On Mon, Nov 5, 2018 at 4:32 PM Bart Van Assche <bvanass...@acm.org> wrote:
> >
> > On Mon, 2018-11-05 at 16:11 -0800, Alexander Duyck wrote:
> > > If we really don't care then why even bother with the switch statement
> > > anyway? It seems like you could just do one ternary operator and be
> > > done with it. Basically all you need is:
> > > return (defined(CONFIG_ZONE_DMA) && (flags & __GFP_DMA)) ? KMALLOC_DMA :
> > > (flags & __GFP_RECLAIMABLE) ? KMALLOC_RECLAIM : 0;
> > >
> > > Why bother with all the extra complexity of the switch statement?
> >
> > I don't think that defined() can be used in a C expression. Hence the
> > IS_ENABLED() macro. If you fix that, leave out four superfluous parentheses,
> > test your patch, post that patch and cc me then I will add my Reviewed-by.
>
> Actually the defined macro is used multiple spots in if statements
> throughout the kernel.
The only 'if (defined(' matches I found in the kernel tree that are not
preprocessor statements occur in Perl code. Maybe I overlooked something?
> The reason for IS_ENABLED is to address the fact that we can be
> dealing with macros that indicate if they are built in or a module
> since those end up being two different defines depending on if you
> select 'y' or 'm'.
>From Documentation/process/coding-style.rst:
Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
symbol into a C boolean expression, and use it in a normal C conditional:
.. code-block:: c
if (IS_ENABLED(CONFIG_SOMETHING)) {
...
}
Bart.
