linux-kernel - Re: [PULL] Wrapper macros for struct task_struct and struct mm

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Date:	Thu, 12 Mar 2009 02:24:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PULL] Wrapper macros for struct task_struct and struct
 mm_struct cpumask transition

On Thu, 12 Mar 2009 19:43:02 +1030 Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Thursday 12 March 2009 18:07:09 Andrew Morton wrote:
> > On Thu, 12 Mar 2009 17:45:22 +1030 Rusty Russell <rusty@...tcorp.com.au> wrote:
> ...
> > Please prefer to put the patches in the email if practical?  More
> > eyeballs and all that.
> 
> Hmm, yes.  Is there a preferred way of doing that with git request-pull?
> Or just append the diff?

You're asking me about git?

> > : +/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
> > : +#define mm_cpumask(mm) (&(mm)->cpu_vm_mask)
> > : +
> ...
> > It would be pretty perverse to run tsk_cpumask() against a `struct
> > cpuset*', but your proposed implementation would merrily permit that
> > mistake.
> > 
> > Can we write the kernel in C please??
> 
> You mean use an inline?  No, it's a bad idea for two reasons.  The minor
> reason is that this macro is a temporary so it makes more sense to fix the
> final version.
> 
> But the major one is const correctness.  Macros give a const value for
> const input.

hm.  Sounds weaselly.

>  We can enhance the macro to check, but that's even uglier:
> 
>   static inline int check_is_task_struct(const struct task_struct *t) { }
>   #define tsk_cpumask(t) (sizeof(check_is_task_struct(t)), &(t)->cpu_vm_mask)

include/linux/typecheck.h has help?

> > yup, the patches are quite safe and mergeable.  And if they'd been in the
> > email body, Linus might have seen that and pulled them ;)
> 
> Probably not, as that's not what he complained about last time.

Linus?  Complain?

>  He might have
> been enlightened by the commit messages tho.

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