* Sasha Levin (levinsasha...@gmail.com) wrote:
> On 09/26/2012 03:59 PM, Steven Rostedt wrote:
> > On Wed, 2012-09-26 at 14:45 +0100, David Laight wrote:
> >> Amazing how something simple gets lots of comments and versions :-)
> >>
> >>> ...
> >>> + * This has to be a macro since HASH_BITS() will not work on pointers
> >>> since
> >>> + * it calculates the size during preprocessing.
> >>> + */
> >>> +#define hash_empty(hashtable)
> >>> \
> >>> +({
> >>> \
> >>> + int __i;
> >>> \
> >>> + bool __ret = true;
> >>> \
> >>> +
> >>> \
> >>> + for (__i = 0; __i < HASH_SIZE(hashtable); __i++)
> >>> \
> >>> + if (!hlist_empty(&hashtable[__i]))
> >>> \
> >>> + __ret = false;
> >>> \
> >>> +
> >>> \
> >>> + __ret;
> >>> \
> >>> +})
> >>
> >> Actually you could have a #define that calls a function
> >> passing in the address and size.
> >
> > Probably would be cleaner to do so.
>
> I think it's worth it if it was more complex than a simple loop. We
> were doing a similar thing with the _size() functions (see version 4
> of this patch), but decided to remove it since it was becoming too
> complex.
Defining local variables within statement-expressions can have some
unexpected side-effects if the "caller" which embeds the macro use the
same variable name. See rcu_dereference() as an example (Paul uses an
awefully large number of underscores). It should be avoided whenever
possible.
> >
> >
> >> Also, should the loop have a 'break' in it?
> >
> > Yeah it should, and could do:
> >
> > for (i = 0; i < HASH_SIZE(hashtable); i++)
> > if (!hlist_empty(&hashtable[i]))
> > break;
> >
> > return i < HASH_SIZE(hashtable);
Hrm, Steven, did you drink you morning coffee before writing this ? ;-)
It looks like you did 2 bugs in 4 LOC.
First, the condition should be reversed, because this function returns
whether the hash is empty, not the other way around.
And even then, if we would do:
for (i = 0; i < HASH_SIZE(hashtable); i++)
if (!hlist_empty(&hashtable[i]))
break;
return i >= HASH_SIZE(hashtable);
What happens if the last entry of the table is non-empty ?
So I would advise that Sasha keep his original flag-based
implementation, but add the missing break, and move the init and empty
define loops into static inlines.
Thanks,
Mathieu
>
> Right.
>
>
> Thanks,
> Sasha
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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