netdev - Re: [PATCH net v4 1/2] net/sched: Restrict conditions for adding duplicating netems to qdisc tree

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Message-ID: <CANn89iLp12_MzcniYqNU2zADVpG8Fs+ZiiMtpV3bCXW2z55DvA@mail.gmail.com>
Date: Tue, 1 Jul 2025 11:11:02 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: Cong Wang <xiyou.wangcong@...il.com>, William Liu <will@...lsroot.io>, netdev@...r.kernel.org, 
	jhs@...atatu.com, victor@...atatu.com, pctammela@...atatu.com, 
	pabeni@...hat.com, kuba@...nel.org, dcaratti@...hat.com, 
	savy@...t3mfailure.io, jiri@...nulli.us, davem@...emloft.net, 
	horms@...nel.org
Subject: Re: [PATCH net v4 1/2] net/sched: Restrict conditions for adding
 duplicating netems to qdisc tree

On Sat, Jun 28, 2025 at 8:15 AM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>

>
>
> Why a whole u32 for one flag?
>
> This increases qdisc_skb_cb from 28 bytes to 32 bytes.
> So still ok, but there should be a build check that it is less than
> space in skb->cb.

I am pretty sure this will break some configs. This has been discussed
in the past.

I would guess drivers/net/amt.c would need some tweaks.

commit bec161add35b478a7746bf58bcdea6faa19129ef
Author: Taehee Yoo <ap420073@...il.com>
Date:   Sun Jan 7 14:42:41 2024 +0000

    amt: do not use overwrapped cb area

Also net/core/filter.c:9740 would complain.