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Subject: Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of
 iterator for list_add() after loop
From:   Jakob Koschel <jakobkoschel@gmail.com>
In-Reply-To: <20220407205426.6a31e4b2@kernel.org>
Date:   Sat, 9 Apr 2022 01:58:29 +0200
Cc:     "David S. Miller" <davem@davemloft.net>,
        Paolo Abeni <pabeni@redhat.com>, Andrew Lunn <andrew@lunn.ch>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        Lars Povlsen <lars.povlsen@microchip.com>,
        Steen Hegelund <Steen.Hegelund@microchip.com>,
        UNGLinuxDriver@microchip.com, Ariel Elior <aelior@marvell.com>,
        Manish Chopra <manishc@marvell.com>,
        Edward Cree <ecree.xilinx@gmail.com>,
        Martin Habets <habetsm.xilinx@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Jiri Pirko <jiri@resnulli.us>,
        Casper Andersson <casper.casan@gmail.com>,
        Bjarni Jonasson <bjarni.jonasson@microchip.com>,
        Colin Ian King <colin.king@intel.com>,
        Michael Walle <michael@walle.cc>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Arnd Bergmann <arnd@arndb.de>,
        Eric Dumazet <edumazet@google.com>,
        Di Zhu <zhudi21@huawei.com>, Xu Wang <vulab@iscas.ac.cn>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, Mike Rapoport <rppt@kernel.org>,
        Brian Johannesmeyer <bjohannesmeyer@gmail.com>,
        Cristiano Giuffrida <c.giuffrida@vu.nl>,
        "Bos, H.J." <h.j.bos@vu.nl>
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References: <20220407102900.3086255-1-jakobkoschel@gmail.com>
 <20220407102900.3086255-3-jakobkoschel@gmail.com>
 <20220407205426.6a31e4b2@kernel.org>
To:     Jakub Kicinski <kuba@kernel.org>
Precedence: bulk

Hello Jakub,

> On 8. Apr 2022, at 05:54, Jakub Kicinski <kuba@kernel.org> wrote:
>=20
> 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 =3D NULL, *iter;
>>=20
>> -		list_for_each_entry(p, &gating_cfg->entries, list) {
>> -			if (p->interval =3D=3D e->interval) {
>> +		list_for_each_entry(iter, &gating_cfg->entries, list) {
>> +			if (iter->interval =3D=3D e->interval) {
>> 				NL_SET_ERR_MSG_MOD(extack,
>> 						   "Gate conflict");
>> 				rc =3D -EBUSY;
>> 				goto err;
>> 			}
>>=20
>> -			if (e->interval < p->interval)
>> +			if (e->interval < iter->interval) {
>> +				p =3D 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);
>=20
> This turns a pretty slick piece of code into something ugly :(
> I'd rather you open coded the iteration here than make it more=20
> complex to satisfy "safe coding guidelines".

I'm not entirely sure I understand what you mean with=20
"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.

>=20
> 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=
/