On Wed, 9 Apr 2014 13:16:38 +0200 Peter Zijlstra <[email protected]> wrote:
> On Wed, Feb 26, 2014 at 02:25:34PM -0800, Andrew Morton wrote:
> > Is there anything we can do to make all this clearer? Simply using a
> > distinctive variable name ("__wait_var__"?) in place of __ret (and
> > documenting it) would help a lot.
> >
> > Some __ret's are long and some are int. Maybe that's a glitch, maybe
> > it's because some __ret's are used for inter-macro communications and
> > some are not, which just makes things worse.
> >
> > I started to do a patch, got all confused and gave up. We've made
> > quite a tangly mess in there, alas.
>
> Something like so?
>
> ---
> Subject: wait: Explain the shadowing and type inconsistencies
> From: Peter Zijlstra <[email protected]>
> Date: Wed Apr 9 12:50:34 CEST 2014
>
> Stick in a comment before someone else tries to fix the sparse warning
> this generates.
>
> Requested-by: Andrew Morton <[email protected]>
> Signed-off-by: Peter Zijlstra <[email protected]>
> Link: http://lkml.kernel.org/n/[email protected]
> ---
> include/linux/wait.h | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -191,11 +191,23 @@ wait_queue_head_t *bit_waitqueue(void *,
> (!__builtin_constant_p(state) || \
> state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE) \
>
> +/*
> + * The below macro ___wait_event() has an explicit shadow of the __ret
> + * variable when used from the wait_event_*() macros.
> + *
> + * This is so that both can use the ___wait_cond_timeout() construct
> + * to wrap the condition.
> + *
> + * The type inconsistency of the wait_event_*() __ret variable is also
> + * on purpose; we use long where we can return timeout values and int
> + * otherwise.
> + */
> +
> #define ___wait_event(wq, condition, state, exclusive, ret, cmd) \
> ({ \
> __label__ __out; \
> wait_queue_t __wait; \
> - long __ret = ret; \
> + long __ret = ret; /* explicit shadow */ \
> \
> INIT_LIST_HEAD(&__wait.task_list); \
> if (exclusive) \
Looks nice to me, thanks.
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