netdev - Re: [PATCH net 1/2] net: ipv6: seg6_iptunnel: set tunnel headroom to zero

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Date:   Sat, 8 Feb 2020 12:34:23 -0500
From:   Alexander Aring <alex.aring@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        netdev@...r.kernel.org, andrea.mayer@...roma2.it,
        dav.lebrun@...il.com, mcr@...delman.ca, stefan@...enfreihafen.org
Subject: Re: [PATCH net 1/2] net: ipv6: seg6_iptunnel: set tunnel headroom to
 zero

Hi,

On Thu, Feb 06, 2020 at 01:54:18PM +0100, David Miller wrote:
> From: Alexander Aring <alex.aring@...il.com>
> Date: Tue,  4 Feb 2020 12:30:18 -0500
> 
> > diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> > index ab7f124ff5d7..5b6e88f16e2d 100644
> > --- a/net/ipv6/seg6_iptunnel.c
> > +++ b/net/ipv6/seg6_iptunnel.c
> > @@ -449,8 +449,6 @@ static int seg6_build_state(struct nlattr *nla,
> >  	if (tuninfo->mode != SEG6_IPTUN_MODE_L2ENCAP)
> >  		newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
> >  
> > -	newts->headroom = seg6_lwt_headroom(tuninfo);
> > -
> >  	*ts = newts;
> >  
> >  	return 0;
> 
> Even if this change is correct, you are eliminating the one and only
> user of seg6_lwt_headroom() so you would have to kill that in this
> patch as well.

Okay, this is in include/uapi but surrounding by __KERNEL__ so I guess
it's still okay to remove it?

btw: why it is not static in seg6_iptunnel.c then?

Anyway I will wait until I hear something back what the use of headroom
exactly is and why the original authors of segmentation routing sets it.
In my case it will simple not work with a IPv6 min mtu so I will set it
to zero for possible net-next patches.

- Alex