linux-kernel - Re: [PATCH 21/31] blk-throttle: implement sq_to_tg(), sq_to_td() and throtl

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Message-ID: <20130506203827.GE800@mtj.dyndns.org>
Date:	Mon, 6 May 2013 13:38:27 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 21/31] blk-throttle: implement sq_to_tg(), sq_to_td() and
 throtl_log()

On Mon, May 06, 2013 at 01:36:44PM -0400, Vivek Goyal wrote:
> On Wed, May 01, 2013 at 05:39:39PM -0700, Tejun Heo wrote:
> 
> [..]
> > +#define throtl_log(sq, fmt, args...)	do {				\
> > +	struct throtl_grp *__tg = sq_to_tg((sq));			\
> > +	struct throtl_data *__td = sq_to_td((sq));			\
> >  	char __pbuf[128];						\
> >  									\
> > -	blkg_path(tg_to_blkg(tg), __pbuf, sizeof(__pbuf));		\
> > -	blk_add_trace_msg((tg)->td->queue, "throtl %s " fmt, __pbuf, ##args); \
> > +	__pbuf[0] = ' ';						\
> > +	__pbuf[1] = '\0';						\
> > +	if ((__tg))							\
> > +		blkg_path(tg_to_blkg(__tg), __pbuf + 1, sizeof(__pbuf) - 1); \
> > +	blk_add_trace_msg(__td->queue, "throtl%s" fmt, __pbuf, ##args); \
> 
> We need one extra space ("throtl%s "), otherwise all the messages
> start right after cgroup path. We need a space between cgroup path
> and actual message.

Okay, we don't - __pbuf[0] = ' '.  The reason it's doing the above
instead of "throtl %s " is because when the path is nil, we don't
wanna print out two consecutive spaces, so AFAICS the code is correct.

Thanks.

-- 
tejun
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