Re: can we get rid of the cpumask_t typedef?

[Linus Torvalds]

On Thu, Nov 21, 2019 at 12:55 AM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
>
> The cpumask_t alias for "struct cpumask" doesn't seem to qualify for the
> kernel's requirement for when a typedef is warranted. It's also somewhat
> easily confused with cpumask_var_t which has very good reasons for being
> a typedef. "struct cpumask" outnumbers "cpumask_t" about 5:2.
>
> The motivation for this is that kbuild informed me about some driver
> that I just enabled for ARM happens to include asm/irq.h, and for magic
> reasons no other previous header happens to pull in cpumask.h. So the
> build fails
>
> >> arch/arm/include/asm/irq.h:34:50: error: unknown type name 'cpumask_t'
>     extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,

Yes. Please just add a forward declaration of 'struct cpumask', and
change that cpumask_t to use that instead.

I'm not sure we need to remove it entirely (there's a fair number of
users), but we can/should deprecate it, and certainly use 'struct
cpumask' in function declarations etc so that you don't need to go
through some include file hell.

           Linus