netdev - Re: [patch net-next RFC 1/9] net_sch: red: Add offload ability to RED qdisc

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Date:   Tue, 31 Oct 2017 08:41:51 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Ahern <dsahern@...il.com>
Cc:     Nogah Frankel <nogahf@...lanox.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        mlxsw <mlxsw@...lanox.com>, "andrew@...n.ch" <andrew@...n.ch>,
        "vivien.didelot@...oirfairelinux.com" 
        <vivien.didelot@...oirfairelinux.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "ganeshgr@...lsio.com" <ganeshgr@...lsio.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Matan Barak <matanb@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "simon.horman@...ronome.com" <simon.horman@...ronome.com>,
        "pieter.jansenvanvuuren@...ronome.com" 
        <pieter.jansenvanvuuren@...ronome.com>,
        "john.hurley@...ronome.com" <john.hurley@...ronome.com>,
        "alexander.h.duyck@...el.com" <alexander.h.duyck@...el.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>
Subject: Re: [patch net-next RFC 1/9] net_sch: red: Add offload ability to
 RED qdisc

Mon, Oct 30, 2017 at 08:24:20PM CET, dsahern@...il.com wrote:
>On 10/30/17 7:54 AM, Nogah Frankel wrote:
>>>> diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
>>>> index 0e88cc2..743c42a 100644
>>>> --- a/include/uapi/linux/pkt_sched.h
>>>> +++ b/include/uapi/linux/pkt_sched.h
>>>> @@ -255,6 +255,7 @@ struct tc_red_qopt {
>>>>  #define TC_RED_ECN		1
>>>>  #define TC_RED_HARDDROP		2
>>>>  #define TC_RED_ADAPTATIVE	4
>>>> +#define TC_RED_OFFLOADED	8
>>>>  };
>>>>
>>>>  struct tc_red_xstats {
>>>
>>> What keeps a user from setting this flag in the tc_red_qopt it
>>> passes into the a change operation?
>> 
>> Nothing keeps the user from doing it, but it has no effect.
>> The decision to offload is the driver's only.
>> It is basically a read-only flag.
>> 
>
>If it is read-only, then attempts to set it from userspace should cause
>the command to fail.

That breaks uapi. Consider existing userspace app sending garbage in
that bit and new kernel which randomly fails upon the garbage.