> On 16 Jun 2017, at 10:44 PM, Daniel Borkmann <dan...@iogearbox.net> wrote:
>
> On 06/15/2017 05:54 AM, Peter Dawson wrote:
>> On Thu, 15 Jun 2017 10:30:29 +0800
>> Haishuang Yan <yanhaishu...@cmss.chinamobile.com> wrote:
>>
>>> Same as ip_gre, geneve and vxlan, use key->tos as tos value.
>>>
>>> CC: Peter Dawson <peted...@gmail.com>
>>> Fixes: 0e9a709560db ("ip6_tunnel, ip6_gre: fix setting of DSCP on
>>> encapsulated packets”)
>>> Suggested-by: Daniel Borkmann <dan...@iogearbox.net>
>>> Signed-off-by: Haishuang Yan <yanhaishu...@cmss.chinamobile.com>
>>>
>>> ---
>>> Changes since v2:
>>> * Add fixes information
>>> * mask key->tos with RT_TOS() suggested by Daniel
>>> ---
>>> net/ipv6/ip6_tunnel.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
>>> index ef99d59..6400726 100644
>>> --- a/net/ipv6/ip6_tunnel.c
>>> +++ b/net/ipv6/ip6_tunnel.c
>>> @@ -1249,7 +1249,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct
>>> net_device *dev, __u8 dsfield,
>>> fl6.flowi6_proto = IPPROTO_IPIP;
>>> fl6.daddr = key->u.ipv6.dst;
>>> fl6.flowlabel = key->label;
>>> - dsfield = ip6_tclass(key->label);
>>> + dsfield = RT_TOS(key->tos);
>>> } else {
>>> if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
>>> encap_limit = t->parms.encap_limit;
>>> @@ -1320,7 +1320,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct
>>> net_device *dev, __u8 dsfield,
>>> fl6.flowi6_proto = IPPROTO_IPV6;
>>> fl6.daddr = key->u.ipv6.dst;
>>> fl6.flowlabel = key->label;
>>> - dsfield = ip6_tclass(key->label);
>>> + dsfield = RT_TOS(key->tos);
>>> } else {
>>> offset = ip6_tnl_parse_tlv_enc_lim(skb,
>>> skb_network_header(skb));
>>> /* ip6_tnl_parse_tlv_enc_lim() might have reallocated skb->head
>>> */
>>
>> I don't think it is correct to apply RT_TOS
>>
>> Here is my understanding based on the RFCs.
>>
>> IPv4/6 Header:0 |0 1 2 3 |0 1 2 3 |0 1 2 3 |0 1 2 3 |
>> RFC2460(IPv6) |Version | Traffic Class | |
>> RFC2474(IPv6) |Version | DSCP |ECN| |
>> RFC2474(IPv4) |Version | IHL | DSCP |ECN|
>> RFC1349(IPv4) |Version | IHL | PREC | TOS |X|
>> RFC791 (IPv4) |Version | IHL | TOS |
>>
>> u8 key->tos stores the full 8bits of Traffic class from an IPv6 header and;
>> u8 key->tos stores the full 8bits of TOS(RFC791) from an IPv4 header
>> u8 ip6_tclass will return the full 8bits of Traffic Class from an IPv6
>> flowlabel
>>
>> RT_TOS will return the RFC1349 4bit TOS field.
>>
>> Applying RT_TOS to a key->tos will result in lost information and the
>> inclusion of 1 bit of ECN if the original field was a DSCP+ECN.
>>
>> Based on this understanding of the RFCs (but not years of experience) and
>> since RFC1349 has been obsoleted by RFC2474 I think the use of RT_TOS should
>> be deprecated.
>>
>> This being said, dsfield = ip6_tclass(key->label) = key->tos isn't fully
>> correct either because the result will contain the ECN bits as well as the
>> DSCP.
>>
>> I agree that code should be consistent, but not where there is a potential
>> issue.
>
> Yeah, you're right. Looks like initial dsfield = key->tos diff was
> the better choice then, sorry for my confusing comment.
>
> For example, bpf_skb_set_tunnel_key() helper that populates the collect
> metadata as one user of this infra masks the key->label so that it really
> only holds the label meaning previous dsfield = ip6_tclass(key->label)
> will always be 0 in that case unlike key->tos that actually gets populated
> and would propagate it.
>
Okay, I will change the commit back to initial version, thanks everyone.
