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Message-ID: <20210114171429.1402ca3d@carbon>
Date: Thu, 14 Jan 2021 17:14:29 +0100
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: John Fastabend <john.fastabend@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org,
Daniel Borkmann <borkmann@...earbox.net>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
maze@...gle.com, lmb@...udflare.com, shaun@...era.io,
Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com,
Jakub Kicinski <kuba@...nel.org>, eyal.birger@...il.com,
colrack@...il.com, brouer@...hat.com
Subject: Re: [PATCH bpf-next V11 5/7] bpf: drop MTU check when doing TC-BPF
redirect to ingress
On Thu, 14 Jan 2021 01:03:33 -0800
John Fastabend <john.fastabend@...il.com> wrote:
> Jesper Dangaard Brouer wrote:
> > The use-case for dropping the MTU check when TC-BPF does redirect to
> > ingress, is described by Eyal Birger in email[0]. The summary is the
> > ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> > ingress redirect packet and let normal netstack fragment packet as needed.
> >
> > [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
> >
> > V9:
> > - Make net_device "up" (IFF_UP) check explicit in skb_do_redirect
> >
> > V4:
> > - Keep net_device "up" (IFF_UP) check.
> > - Adjustment to handle bpf_redirect_peer() helper
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> > ---
> > include/linux/netdevice.h | 31 +++++++++++++++++++++++++++++--
> > net/core/dev.c | 19 ++-----------------
> > net/core/filter.c | 14 +++++++++++---
> > 3 files changed, 42 insertions(+), 22 deletions(-)
> >
>
> [...]
>
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 3f2e593244ca..1908800b671c 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
> >
> > static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
> > {
> > - return dev_forward_skb(dev, skb);
>
> > + int ret = ____dev_forward_skb(dev, skb, false);
> > +
> > + if (likely(!ret)) {
> > + skb->protocol = eth_type_trans(skb, dev);
> > + skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
> > + ret = netif_rx(skb);
> > + }
> > +
> > + return ret;
>
> How about putting above block into a dev.c routine call it
>
> dev_forward_skb_nomtu(...)
>
> or something like that. Then we keep this code next to its pair
> with mtu check, dev_forward_skb().
>
> dev_forward_skb() also uses netif_rx_internal() looks like maybe we should
> just do the same here?
I love the idea. I'm coding it up and it looks much nicer. And yes we
obviously can use netif_rx_internal() once the code in core/dev.c
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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