netdev - Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to gre

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Message-ID: <20220315215553.676a5d24@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 15 Mar 2022 21:55:53 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Ahern <dsahern@...nel.org>
Cc:     menglong8.dong@...il.com, rostedt@...dmis.org, mingo@...hat.com,
        xeb@...l.ru, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        imagedong@...cent.com, edumazet@...gle.com, kafai@...com,
        talalahmad@...gle.com, keescook@...omium.org, alobakin@...me,
        flyingpeng@...cent.com, mengensun@...cent.com,
        dongli.zhang@...cle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Biao Jiang <benbjiang@...cent.com>
Subject: Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to
 gre_rcv()

On Tue, 15 Mar 2022 21:49:01 -0600 David Ahern wrote:
> >>  	ver = skb->data[1]&0x7f;
> >> -	if (ver >= GREPROTO_MAX)
> >> +	if (ver >= GREPROTO_MAX) {
> >> +		reason = SKB_DROP_REASON_GRE_VERSION;  
> > 
> > TBH I'm still not sure what level of granularity we should be shooting
> > for with the reasons. I'd throw all unexpected header values into one 
> > bucket, not go for a reason per field, per protocol. But as I'm said
> > I'm not sure myself, so we can keep what you have..  
> 
> I have stated before I do not believe every single drop point in the
> kernel needs a unique reason code. This is overkill. The reason augments
> information we already have -- the IP from kfree_skb tracepoint.

That's certainly true. I wonder if there is a systematic way of
approaching these additions that'd help us picking the points were 
we add reasons less of a judgment call.