linux-kernel - Re: [PATCH 3/6] gfs2: simplify current_tail() via list_last_entry_or

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Message-ID: <20131115163957.GA28467@redhat.com>
Date:	Fri, 15 Nov 2013 17:39:57 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jeff Liu <jeff.liu@...cle.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	"xfs@....sgi.com" <xfs@....sgi.com>, cluster-devel@...hat.com,
	linux-mtd@...ts.infradead.org,
	jfs-discussion@...ts.sourceforge.net, jiri@...nulli.us,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 3/6] gfs2: simplify current_tail() via
	list_last_entry_or_null()

On 11/15, Jeff Liu wrote:
>
> @@ -441,13 +441,9 @@ static unsigned int current_tail(struct gfs2_sbd *sdp)
>  
>  	spin_lock(&sdp->sd_ail_lock);
>  
> -	if (list_empty(&sdp->sd_ail1_list)) {
> -		tail = sdp->sd_log_head;
> -	} else {
> -		tr = list_entry(sdp->sd_ail1_list.prev, struct gfs2_trans,
> -				tr_list);
> -		tail = tr->tr_first;
> -	}
> +	tr = list_last_entry_or_null(&sdp->sd_ail1_list, struct gfs2_trans,
> +				     tr_list);
> +	tail = tr ? tr->tr_first : sdp->sd_log_head;
>  

Personally I agree with Steven. At least in this case
list_last_entry_or_null() doesn't really help to simplify the code.

But probably list_last_entry() makes sense in the "else" branch,
athough this is minor.


Off-topic. Not sure this really makes sense, but I was thinking about

	list_get_first(pos, head, member)	\
		((pos) = list_first_entry(head, typeof(*pos), member))

and list_get_first() last of course. The obvious advantage is that
compared to

	tr = list_last_entry(sdp->sd_ail1_list, struct gfs2_trans, tr_list);

above you do not need to type "struct gfs2_trans",

	list_get_last(tr, sdp->sd_ail1_list, tr_list);

looks a bit better.

Oleg.

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