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Date: Wed, 1 Jul 2015 22:22:26 -0400
From: Tejun Heo <tj@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, hch@infradead.org,
        hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, vgoyal@redhat.com,
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Subject: Re: [PATCH 36/51] writeback: implement bdi_for_each_wb()
Message-ID: <20150702022226.GH26440@mtj.duckdns.org>
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On Wed, Jul 01, 2015 at 09:27:57AM +0200, Jan Kara wrote:
> > +#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id)		\
> > +	for ((iter)->next_id = (start_blkcg_id);			\
> > +	     ({	(wb_cur) = !(iter)->next_id++ ? &(bdi)->wb : NULL; }); )
> > +
> 
> This looks quite confusing. Won't it be easier to understand as:
> 
> struct wb_iter {
> } __attribute__ ((unused));
> 
> #define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id) \
>   if (((wb_cur) = (!start_blkcg_id ? &(bdi)->wb : NULL)))

But then break or continue wouldn't work as expected.  It can get
really confusing when it's wrapped by an outer loop.

Thanks.

-- 
tejun

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 36/51] writeback: implement bdi_for_each_wb()
Date: Wed, 1 Jul 2015 22:22:26 -0400
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References: <1432329245-5844-1-git-send-email-tj@kernel.org>
 <1432329245-5844-37-git-send-email-tj@kernel.org>
 <20150701072757.GW7252@quack.suse.cz>
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Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, hch@infradead.org,
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	vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org,
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To: Jan Kara <jack@suse.cz>
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On Wed, Jul 01, 2015 at 09:27:57AM +0200, Jan Kara wrote:
> > +#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id)		\
> > +	for ((iter)->next_id = (start_blkcg_id);			\
> > +	     ({	(wb_cur) = !(iter)->next_id++ ? &(bdi)->wb : NULL; }); )
> > +
> 
> This looks quite confusing. Won't it be easier to understand as:
> 
> struct wb_iter {
> } __attribute__ ((unused));
> 
> #define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id) \
>   if (((wb_cur) = (!start_blkcg_id ? &(bdi)->wb : NULL)))

But then break or continue wouldn't work as expected.  It can get
really confusing when it's wrapped by an outer loop.

Thanks.

-- 
tejun

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