netdev - Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable

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Date:	Tue, 04 Sep 2012 11:35:48 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Sasha Levin <levinsasha928@...il.com>, Tejun Heo <tj@...nel.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net, mingo@...e.hu,
	ebiederm@...ssion.com, aarcange@...hat.com, ericvh@...il.com,
	netdev@...r.kernel.org, josh@...htriplett.org,
	eric.dumazet@...il.com, axboe@...nel.dk, agk@...hat.com,
	dm-devel@...hat.com, neilb@...e.de, ccaulfie@...hat.com,
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	bfields@...ldses.org, fweisbec@...il.com, jesse@...ira.com,
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	dev@...nvswitch.org, rds-devel@....oracle.com, lw@...fujitsu.com
Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive
 hashtable

On Tue, 2012-08-28 at 19:00 -0400, Mathieu Desnoyers wrote:

> Looking again at:
> 
> +#define hash_for_each_size(name, bits, bkt, node, obj, member)                 \
> +       for (bkt = 0; bkt < HASH_SIZE(bits); bkt++)                             \
> +               hlist_for_each_entry(obj, node, &name[bkt], member)
> 
> you will notice that a "break" or "continue" in the inner loop will not
> affect the outer loop, which is certainly not what the programmer would
> expect!
> 
> I advise strongly against creating such error-prone construct.
> 

A few existing loop macros do this. But they require a do { } while ()
approach, and all have a comment.

It's used by do_each_thread() in sched.h and ftrace does this as well.
Look at kernel/trace/ftrace.c at do_for_each_ftrace_rec().

Yes it breaks 'break' but it does not break 'continue' as it would just
go to the next item that would have been found (like a normal for
would).

-- Steve


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