netdev - Re: [PATCH net-next v4 1/2] net sched actions: dump more than TCA_ACT_MAX

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Message-ID: <1492690694.22296.32.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 20 Apr 2017 05:18:14 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, davem@...emloft.net,
        netdev@...r.kernel.org, xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next v4 1/2] net sched actions: dump more than
 TCA_ACT_MAX_PRIO actions per batch

On Thu, 2017-04-20 at 06:42 -0400, Jamal Hadi Salim wrote:

> 
> They are not the same issue Jiri. We have used bitmasks fine on netlink
> message for a millenia. Nobody sets garbage on a bitmask they are not
> supposed to touch. The struct padding thing is a shame the way it
> turned out - now netlink can no longer have a claim to be a (good)
> wire protocol.

Except that users wrote programs, and these programs work today.

By changing the kernel and recognizing new flags in existing padding,
you might break the programs.

This is not acceptable. Period.

Had we checked the padding being 0 in old kernels, this change would
have been possible today.

But because old kernels did not care of the padding contents, then there
is no way new kernel can suddenly trust them at all.

Please Jamal, you have to forget this nonsense.