linux-kernel - Re: [PATCH net-next v6] net: openvswitch: IPv6: Add IPv6 extension header support

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Message-ID: <CAASuNyVe8z1R6xyCfSAxZbcrL3dej1n8TXXkqS-e8QvA6eWd+w@mail.gmail.com>
Date:   Thu, 30 Sep 2021 09:11:48 -0700
From:   Cpp Code <cpp.code.lv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        netdev@...r.kernel.org, pshelar@....org,
        "David S. Miller" <davem@...emloft.net>,
        ovs dev <dev@...nvswitch.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6] net: openvswitch: IPv6: Add IPv6 extension
 header support

On Wed, Sep 29, 2021 at 6:19 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 29 Sep 2021 08:19:05 +0200 Nicolas Dichtel wrote:
> > > /* Insert a kernel only KEY_ATTR */
> > > #define OVS_KEY_ATTR_TUNNEL_INFO    __OVS_KEY_ATTR_MAX
> > > #undef OVS_KEY_ATTR_MAX
> > > #define OVS_KEY_ATTR_MAX            __OVS_KEY_ATTR_MAX
> > Following the other thread [1], this will break if a new app runs over an old
> > kernel.
>
> Good point.
>
> > Why not simply expose this attribute to userspace and throw an error if a
> > userspace app uses it?
>
> Does it matter if it's exposed or not? Either way the parsing policy
> for attrs coming from user space should have a reject for the value.
> (I say that not having looked at the code, so maybe I shouldn't...)

To remove some confusion, there are some architectural nuances if we
want to extend code without large refactor.
The ovs_key_attr is defined only in kernel side. Userspace side is
generated from this file. As well the code can be built without kernel
modules.
The code inside OVS repository and net-next is not identical, but I
try to keep some consistency.

JFYI This is the file responsible for generating userspace part:
https://github.com/openvswitch/ovs/blob/master/build-aux/extract-odp-netlink-h
This is the how corresponding file for ovs_key_attr looks inside OVS:
https://github.com/openvswitch/ovs/blob/master/datapath/linux/compat/include/linux/openvswitch.h
one can see there are more values than in net-next version.