linux-kernel - Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of iterator for list

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Date:   Sat, 9 Apr 2022 01:58:29 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Ariel Elior <aelior@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Casper Andersson <casper.casan@...il.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Colin Ian King <colin.king@...el.com>,
        Michael Walle <michael@...le.cc>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Di Zhu <zhudi21@...wei.com>, Xu Wang <vulab@...as.ac.cn>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of
 iterator for list_add() after loop

Hello Jakub,

> On 8. Apr 2022, at 05:54, Jakub Kicinski <kuba@...nel.org> wrote:
> 
> On Thu,  7 Apr 2022 12:28:47 +0200 Jakob Koschel wrote:
>> diff --git a/drivers/net/dsa/sja1105/sja1105_vl.c b/drivers/net/dsa/sja1105/sja1105_vl.c
>> index b7e95d60a6e4..cfcae4d19eef 100644
>> --- a/drivers/net/dsa/sja1105/sja1105_vl.c
>> +++ b/drivers/net/dsa/sja1105/sja1105_vl.c
>> @@ -27,20 +27,24 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
>> 	if (list_empty(&gating_cfg->entries)) {
>> 		list_add(&e->list, &gating_cfg->entries);
>> 	} else {
>> -		struct sja1105_gate_entry *p;
>> +		struct sja1105_gate_entry *p = NULL, *iter;
>> 
>> -		list_for_each_entry(p, &gating_cfg->entries, list) {
>> -			if (p->interval == e->interval) {
>> +		list_for_each_entry(iter, &gating_cfg->entries, list) {
>> +			if (iter->interval == e->interval) {
>> 				NL_SET_ERR_MSG_MOD(extack,
>> 						   "Gate conflict");
>> 				rc = -EBUSY;
>> 				goto err;
>> 			}
>> 
>> -			if (e->interval < p->interval)
>> +			if (e->interval < iter->interval) {
>> +				p = iter;
>> +				list_add(&e->list, iter->list.prev);
>> 				break;
>> +			}
>> 		}
>> -		list_add(&e->list, p->list.prev);
>> +		if (!p)
>> +			list_add(&e->list, gating_cfg->entries.prev);
> 
> This turns a pretty slick piece of code into something ugly :(
> I'd rather you open coded the iteration here than make it more 
> complex to satisfy "safe coding guidelines".

I'm not entirely sure I understand what you mean with 
"open coded the iteration". But maybe the solution proposed by Vladimir [1]
works for you? I'm planning to rewrite the cases in that way for the relevant
ones.

> 
> Also the list_add() could be converted to list_add_tail().

Good point, I wasn't sure if that's considered as something that should be
done as a separate change. I'm happy to include it in v2.

Thanks for the input.

	Jakob

[1] https://lore.kernel.org/linux-kernel/20220408114120.tvf2lxvhfqbnrlml@skbuf/