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

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Message-Id: <200903121943.02799.rusty@rustcorp.com.au>
Date:	Thu, 12 Mar 2009 19:43:02 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 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?

> : +/* 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.  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)

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

Cheers,
Rusty.
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