linux-kernel - Re: Routing loops & TTL tracking with tunnel devices

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Message-ID: <YmxTo2hVwcwhdvjO@zx2c4.com>
Date:   Fri, 29 Apr 2022 23:07:47 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, kuba@...nel.org,
        hannes@...essinduktion.org, edumazet@...gle.com
Subject: Re: Routing loops & TTL tracking with tunnel devices

Hi Eric,

On Fri, Apr 29, 2022 at 01:54:27PM -0700, Eric Dumazet wrote:
> > Anyway, it'd be nice if there were a free u8 somewhere in sk_buff that I
> > could use for tracking times through the stack. Other kernels have this
> > but afaict Linux still does not. I looked into trying to overload some
> > existing fields -- tstamp/skb_mstamp_ns or queue_mapping -- which I was
> > thinking might be totally unused on TX?
> 
> 
> if skbs are stored in some internal wireguard queue, can not you use 
> skb->cb[],
> 
> like many other layers do ?

This isn't for some internal wireguard queue. The packets get sent out
of udp_tunnel_xmit_skb(), so they leave wireguard's queues.

Jason