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SubjectRe: [net-next v5 1/2] seg6: inherit DSCP of inner IPv4 packets
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On 26/08/2020 21:41, David Ahern wrote:
> On 8/26/20 6:12 AM, Ahmed Abdelsalam wrote:
>>
>> On 26/08/2020 02:45, David Ahern wrote:
>>> On 8/25/20 5:45 PM, Ahmed Abdelsalam wrote:
>>>>
>>>> Hi David
>>>>
>>>> The seg6 encap is implemented through the seg6_lwt rather than
>>>> seg6_local_lwt.
>>>
>>> ok. I don't know the seg6 code; just taking a guess from a quick look.
>>>
>>>> We can add a flag(SEG6_IPTUNNEL_DSCP) in seg6_iptunnel.h if we do not
>>>> want to go the sysctl direction.
>>>
>>> sysctl is just a big hammer with side effects.
>>>
>>> It struck me that the DSCP propagation is very similar to the TTL
>>> propagation with MPLS which is per route entry (MPLS_IPTUNNEL_TTL and
>>> stored as ttl_propagate in mpls_iptunnel_encap). Hence the question of
>>> whether SR could make this a per route attribute. Consistency across
>>> implementations is best.
>>> SRv6 does not have an issue of having this per route.
>> Actually, as SRv6 leverage IPv6 encapsulation, I would say it should
>> consistent with ip6_tunnel not MPLS.
>>
>> In ip6_tunnel, both ttl and flowinfo (tclass and flowlabel) are provided.
>>
>> Ideally, SRv6 code should have done the same with:
>> TTL       := VLAUE | DEFAULT | inherit.
>> TCLASS    := 0x00 .. 0xFF | inherit
>> FLOWLABEL := { 0x00000 .. 0xfffff | inherit | compute.
>>
>
> New attributes get added all the time. Why does something like this now
> work for these features:
>
> diff --git a/include/uapi/linux/seg6_iptunnel.h
> b/include/uapi/linux/seg6_iptunnel.h
> index eb815e0d0ac3..b628333ba100 100644
> --- a/include/uapi/linux/seg6_iptunnel.h
> +++ b/include/uapi/linux/seg6_iptunnel.h
> @@ -20,6 +20,8 @@
> enum {
> SEG6_IPTUNNEL_UNSPEC,
> SEG6_IPTUNNEL_SRH,
> + SEG6_IPTUNNEL_TTL, /* u8 */
> + SEG6_IPTUNNEL_TCLASS, /* u8 */
> __SEG6_IPTUNNEL_MAX,
> };
> #define SEG6_IPTUNNEL_MAX (__SEG6_IPTUNNEL_MAX - 1)
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> index 897fa59c47de..7cb512b65bc3 100644
> --- a/net/ipv6/seg6_iptunnel.c
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -46,6 +46,11 @@ static size_t seg6_lwt_headroom(struct
> seg6_iptunnel_encap *tuninfo)
>
> struct seg6_lwt {
> struct dst_cache cache;
> + u8 ttl_propagate; /* propagate ttl from inner header */
> + u8 default_ttl; /* ttl value to use */
> + u8 tclass_inherit; /* inherit tclass from inner header */
> + u8 tclass; /* tclass value to use */
> +
> struct seg6_iptunnel_encap tuninfo[];
> };
>
> @@ -61,7 +66,10 @@ seg6_encap_lwtunnel(struct lwtunnel_state *lwt)
> }
>
> static const struct nla_policy seg6_iptunnel_policy[SEG6_IPTUNNEL_MAX +
> 1] = {
> - [SEG6_IPTUNNEL_SRH] = { .type = NLA_BINARY },
> + [SEG6_IPTUNNEL_UNSPEC] = { .strict_start_type =
> SEG6_IPTUNNEL_SRH + 1 },
> + [SEG6_IPTUNNEL_SRH] = { .type = NLA_BINARY },
> + [SEG6_IPTUNNEL_TTL] = { .type = NLA_U8 },
> + [SEG6_IPTUNNEL_TCLASS] = { .type = NLA_U8 },
> };
>
> static int nla_put_srh(struct sk_buff *skb, int attrtype,
> @@ -460,6 +468,22 @@ static int seg6_build_state(struct net *net, struct
> nlattr *nla,
>
> memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);
>
> + if (tb[SEG6_IPTUNNEL_TTL]) {
> + slwt->default_ttl = nla_get_u8(tb[SEG6_IPTUNNEL_TTL]);
> + slwt->ttl_propagate = slwt->default_ttl ? 0 : 1;
> + }
> + if (tb[SEG6_IPTUNNEL_TCLASS]) {
> + u32 tmp = nla_get_u32(tb[SEG6_IPTUNNEL_TCLASS]);
> +
> + if (tmp == (u32)-1) {
> + slwt->tclass_inherit = true;
> + } else if (tmp & <some valid range mask>) {
> + error
> + } else {
> + slwt->tclass = ...
> + }
> + }
> +
> newts->type = LWTUNNEL_ENCAP_SEG6;
> newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
>
>
> And the use the values in slwt as needed.
>

Thanks for the suggestions and the code example
I will write the patches and submit to net-next.

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