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