netdev - Re: [PATCH v2 net-next 4/4] net: dsa: tag_dsa: Support reception of packets from LAG devices

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Date:   Wed, 2 Dec 2020 02:33:43 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org, andrew@...n.ch,
        vivien.didelot@...il.com, f.fainelli@...il.com,
        j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 4/4] net: dsa: tag_dsa: Support reception of
 packets from LAG devices

On Tue, Dec 01, 2020 at 11:31:02PM +0100, Tobias Waldekranz wrote:
> >> +	if (unlikely(!dsa_slave_dev_check(skb->dev))) {
> >> +		/* Packet is to be injected directly on an upper
> >> +		 * device, e.g. a team/bond, so skip all DSA-port
> >> +		 * specific actions.
> >> +		 */
> >> +		netif_rx(skb);
> >> +		return 0;
> >
> > netif_rx returns an int code, it seems odd to ignore it.
>
> This is exactly the same treatment that the return code from
> gro_cells_receive gets just a few lines down. They return the same set
> of codes (NET_RX_{SUCCESS,DROP}).
>
> Looking through the source base, there are a few callers that look at
> the return value (the overwhelming majority ignore it). Actions vary
> from printing warnings (without rate-limit, yikes), setting variables
> that are otherwise unused, or bumping a counter (the only reasonable
> thing I have seen).
>
> But looking through enqueue_to_backlog, it seems like there already is a
> counter for this that is accessible from /proc/net/softnet_data.

And also, more obviously, in ndo_get_stats64 (ip -s -s link).

Ok, I think you can ignore the return value.