netdev - Re: [PATCH net] net: Clear local_df only if crossing namespace.

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Message-ID: <20140208005843.GE16198@order.stressinduktion.org>
Date:	Sat, 8 Feb 2014 01:58:43 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"Templin, Fred L" <Fred.L.Templin@...ing.com>,
	nicolas.dichtel@...nd.com
Subject: Re: [PATCH net] net: Clear local_df only if crossing namespace.

[Cc Nicolas]

On Fri, Feb 07, 2014 at 02:49:20PM -0800, Pravin Shelar wrote:
> On Fri, Feb 7, 2014 at 2:28 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> > Hi!
> >
> > On Fri, Feb 07, 2014 at 02:12:38PM -0800, Pravin wrote:
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -3905,12 +3905,13 @@ EXPORT_SYMBOL(skb_try_coalesce);
> >>   */
> >>  void skb_scrub_packet(struct sk_buff *skb, bool xnet)
> >>  {
> >> -     if (xnet)
> >> +     if (xnet) {
> >>               skb_orphan(skb);
> >> +             skb->local_df = 0;
> >> +     }
> >>       skb->tstamp.tv64 = 0;
> >>       skb->pkt_type = PACKET_HOST;
> >>       skb->skb_iif = 0;
> >> -     skb->local_df = 0;
> >>       skb_dst_drop(skb);
> >>       skb->mark = 0;
> >>       secpath_reset(skb);
> >
> > I wonder if this should be the right behaviour for tunnels, which should just
> > do fragmentation based on IP_DF, even if the packet originated locally from a
> > socket which allowed local fragmentation (inet->pmtudisc < IP_PMTUDISC_DO).
> >
> This is not about tunneling, skb_scrub_packet() is generic function
> which should not reset local_df on all packets.
> 
> We can have separate discussion about use of local_df and tunneling in
> another thread.

This change only affects tunnel code as of current net branch, how do
you not expect a discussion about that in this thread, I really wonder?

May I know because of wich vport, vxlan or gre, you did this change?

I am feeling a bit uncomfortable handling remote and local packets that
differently on lower tunnel output (local_df is mostly set on locally
originating packets).

Thanks,

  Hannes

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