netdev - Re: [PATCH net-next v4 2/6] net: sched: Allow extending set of supported RED flags

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Date:   Thu, 12 Mar 2020 21:16:10 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Petr Machata <petrm@...lanox.com>
Cc:     netdev@...r.kernel.org, Roman Mashak <mrv@...atatu.com>,
        Eric Dumazet <eric.dumazet@...il.com>, jhs@...atatu.com,
        xiyou.wangcong@...il.com, davem@...emloft.net, idosch@...lanox.com,
        mlxsw@...lanox.com
Subject: Re: [PATCH net-next v4 2/6] net: sched: Allow extending set of
 supported RED flags

On Fri, 13 Mar 2020 01:10:56 +0200 Petr Machata wrote:
> The qdiscs RED, GRED, SFQ and CHOKE use different subsets of the same pool
> of global RED flags. These are passed in tc_red_qopt.flags. However none of
> these qdiscs validate the flag field, and just copy it over wholesale to
> internal structures, and later dump it back. (An exception is GRED, which
> does validate for VQs -- however not for the main setup.)
> 
> A broken userspace can therefore configure a qdisc with arbitrary
> unsupported flags, and later expect to see the flags on qdisc dump. The
> current ABI therefore allows storage of several bits of custom data to
> qdisc instances of the types mentioned above. How many bits, depends on
> which flags are meaningful for the qdisc in question. E.g. SFQ recognizes
> flags ECN and HARDDROP, and the rest is not interpreted.
> 
> If SFQ ever needs to support ADAPTATIVE, it needs another way of doing it,
> and at the same time it needs to retain the possibility to store 6 bits of
> uninterpreted data. Likewise RED, which adds a new flag later in this
> patchset.
> 
> To that end, this patch adds a new function, red_get_flags(), to split the
> passed flags of RED-like qdiscs to flags and user bits, and
> red_validate_flags() to validate the resulting configuration. It further
> adds a new attribute, TCA_RED_FLAGS, to pass arbitrary flags.
> 
> Signed-off-by: Petr Machata <petrm@...lanox.com>

Reviewed-by: Jakub Kicinski <kuba@...nel.org>