netdev - Re: [PATCH ipsec-next,v2 2/3] xfrm: interface: support collect metadata mode

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Date:   Thu, 25 Aug 2022 18:14:51 +0300
From:   Eyal Birger <eyal.birger@...il.com>
To:     Nikolay Aleksandrov <razor@...ckwall.org>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, steffen.klassert@...unet.com,
        herbert@...dor.apana.org.au, dsahern@...nel.org,
        contact@...elbtn.com, pablo@...filter.org,
        nicolas.dichtel@...nd.com, netdev@...r.kernel.org,
        bpf@...r.kernel.org, "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH ipsec-next,v2 2/3] xfrm: interface: support collect
 metadata mode

On Thu, Aug 25, 2022 at 5:24 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
>
> On 25/08/2022 16:46, Eyal Birger wrote:
> > This commit adds support for 'collect_md' mode on xfrm interfaces.
> >
> > Each net can have one collect_md device, created by providing the
> > IFLA_XFRM_COLLECT_METADATA flag at creation. This device cannot be
> > altered and has no if_id or link device attributes.
> >
> > On transmit to this device, the if_id is fetched from the attached dst
> > metadata on the skb. If exists, the link property is also fetched from
> > the metadata. The dst metadata type used is METADATA_XFRM which holds
> > these properties.
> >
> > On the receive side, xfrmi_rcv_cb() populates a dst metadata for each
> > packet received and attaches it to the skb. The if_id used in this case is
> > fetched from the xfrm state, and the link is fetched from the incoming
> > device. This information can later be used by upper layers such as tc,
> > ebpf, and ip rules.
> >
> > Because the skb is scrubed in xfrmi_rcv_cb(), the attachment of the dst
> > metadata is postponed until after scrubing. Similarly, xfrm_input() is
> > adapted to avoid dropping metadata dsts by only dropping 'valid'
> > (skb_valid_dst(skb) == true) dsts.
> >
> > Policy matching on packets arriving from collect_md xfrmi devices is
> > done by using the xfrm state existing in the skb's sec_path.
> > The xfrm_if_cb.decode_cb() interface implemented by xfrmi_decode_session()
> > is changed to keep the details of the if_id extraction tucked away
> > in xfrm_interface.c.
> >
> > Signed-off-by: Eyal Birger <eyal.birger@...il.com>
> >
> > ----
> >
> > v2:
> >   - add "link" property as suggested by Nicolas Dichtel
> >   - rename xfrm_if_decode_session_params to xfrm_if_decode_session_result
> > ---
>
> (+CC Daniel)
>
> Hi,
> Generally I really like the idea, but I missed to comment the first round. :)
> A few comments below..
>

Thanks for the review!

> >  include/net/xfrm.h           |  11 +++-
<...snip...>
> >
> >  static const struct nla_policy xfrmi_policy[IFLA_XFRM_MAX + 1] = {
> > -     [IFLA_XFRM_LINK]        = { .type = NLA_U32 },
> > -     [IFLA_XFRM_IF_ID]       = { .type = NLA_U32 },
> > +     [IFLA_XFRM_UNSPEC]              = { .strict_start_type = IFLA_XFRM_COLLECT_METADATA },
> > +     [IFLA_XFRM_LINK]                = { .type = NLA_U32 },
>
> link is signed, so s32

Ack on all comments except this one - I'm a little hesitant to change
this one as the change would be unrelated to this series.

Thanks!
Eyal.