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

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Date:   Wed, 29 Sep 2021 08:19:05 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Toms Atteka <cpp.code.lv@...il.com>
Cc:     netdev@...r.kernel.org, pshelar@....org, davem@...emloft.net,
        dev@...nvswitch.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6] net: openvswitch: IPv6: Add IPv6 extension
 header support

Le 29/09/2021 à 02:48, Jakub Kicinski a écrit :
> On Tue, 28 Sep 2021 12:47:27 -0700 Toms Atteka wrote:
>> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
>> index a87b44cd5590..dc6eb5f6399f 100644
>> --- a/include/uapi/linux/openvswitch.h
>> +++ b/include/uapi/linux/openvswitch.h
>> @@ -346,6 +346,13 @@ enum ovs_key_attr {
>>  #ifdef __KERNEL__
>>  	OVS_KEY_ATTR_TUNNEL_INFO,  /* struct ip_tunnel_info */
>>  #endif
>> +
>> +#ifndef __KERNEL__
> 
> #else
> 
>> +	PADDING,  /* Padding so kernel and non kernel field count would match */
> 
> The name PADDING seems rather risky, collisions will be likely.
> OVS_KEY_ATTR_PADDING maybe?
> 
> But maybe we don't need to define this special value and bake it into
> the uAPI, why can't we add something like this to the kernel header
> (i.e. include/linux/openvswitch.h):
> 
> /* 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.
Why not simply expose this attribute to userspace and throw an error if a
userspace app uses it?

[1]
https://lore.kernel.org/lkml/CAASuNyUWoZ1wToEUYbdehux=yVnWQ=suKDyRkQfRD-72DOLziw@mail.gmail.com/

> 
>> +#endif