Re: [net-next v2 1/2] seg6: add NEXT-C-SID support for SRv6 End.X behavior

[Hangbin Liu]

On Sat, Aug 12, 2023 at 08:09:25PM +0200, Andrea Mayer wrote:
> The NEXT-C-SID mechanism described in [1] offers the possibility of
> encoding several SRv6 segments within a single 128 bit SID address. Such
> a SID address is called a Compressed SID (C-SID) container. In this way,
> the length of the SID List can be drastically reduced.
> 
> A SID instantiated with the NEXT-C-SID flavor considers an IPv6 address
> logically structured in three main blocks: i) Locator-Block; ii)
> Locator-Node Function; iii) Argument.
> 
>                         C-SID container
> +------------------------------------------------------------------+
> |     Locator-Block      |Loc-Node|            Argument            |
> |                        |Function|                                |
> +------------------------------------------------------------------+
> <--------- B -----------> <- NF -> <------------- A --------------->
> 
>    (i) The Locator-Block can be any IPv6 prefix available to the provider;
> 
>   (ii) The Locator-Node Function represents the node and the function to
>        be triggered when a packet is received on the node;
> 
>  (iii) The Argument carries the remaining C-SIDs in the current C-SID
>        container.
> 
> This patch leverages the NEXT-C-SID mechanism previously introduced in the
> Linux SRv6 subsystem [2] to support SID compression capabilities in the
> SRv6 End.X behavior [3].
> An SRv6 End.X behavior with NEXT-C-SID flavor works as an End.X behavior
> but it is capable of processing the compressed SID List encoded in C-SID
> containers.
> 
> An SRv6 End.X behavior with NEXT-C-SID flavor can be configured to support
> user-provided Locator-Block and Locator-Node Function lengths. In this
> implementation, such lengths must be evenly divisible by 8 (i.e. must be
> byte-aligned), otherwise the kernel informs the user about invalid
> values with a meaningful error code and message through netlink_ext_ack.
> 
> If Locator-Block and/or Locator-Node Function lengths are not provided
> by the user during configuration of an SRv6 End.X behavior instance with
> NEXT-C-SID flavor, the kernel will choose their default values i.e.,
> 32-bit Locator-Block and 16-bit Locator-Node Function.
> 
> [1] - https://datatracker.ietf.org/doc/html/draft-ietf-spring-srv6-srh-compression
> [2] - https://lore.kernel.org/all/20220912171619.16943-1-andrea.mayer@xxxxxxxxxxx/
> [3] - https://datatracker.ietf.org/doc/html/rfc8986#name-endx-l3-cross-connect
> 
> Signed-off-by: Andrea Mayer <andrea.mayer@xxxxxxxxxxx>
> ---
>  net/ipv6/seg6_local.c | 108 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 88 insertions(+), 20 deletions(-)
> 
> diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
> index dd433cc265c8..24e2b4b494cb 100644
> --- a/net/ipv6/seg6_local.c
> +++ b/net/ipv6/seg6_local.c
> @@ -109,15 +109,19 @@ struct bpf_lwt_prog {
>  #define next_csid_chk_lcnode_fn_bits(flen)		\
>  	next_csid_chk_lcblock_bits(flen)
>  
> +/* flag indicating that flavors are set up for a given End* behavior */
> +#define SEG6_F_LOCAL_FLAVORS		SEG6_F_ATTR(SEG6_LOCAL_FLAVORS)
> +
>  #define SEG6_F_LOCAL_FLV_OP(flvname)	BIT(SEG6_LOCAL_FLV_OP_##flvname)
> +#define SEG6_F_LOCAL_FLV_NEXT_CSID	SEG6_F_LOCAL_FLV_OP(NEXT_CSID)
>  #define SEG6_F_LOCAL_FLV_PSP		SEG6_F_LOCAL_FLV_OP(PSP)
>  
>  /* Supported RFC8986 Flavor operations are reported in this bitmask */
>  #define SEG6_LOCAL_FLV8986_SUPP_OPS	SEG6_F_LOCAL_FLV_PSP
>  
> -/* Supported Flavor operations are reported in this bitmask */
> -#define SEG6_LOCAL_FLV_SUPP_OPS		(SEG6_F_LOCAL_FLV_OP(NEXT_CSID) | \
> +#define SEG6_LOCAL_END_FLV_SUPP_OPS	(SEG6_F_LOCAL_FLV_NEXT_CSID | \
>  					 SEG6_LOCAL_FLV8986_SUPP_OPS)
> +#define SEG6_LOCAL_END_X_FLV_SUPP_OPS	SEG6_F_LOCAL_FLV_NEXT_CSID
>  
>  struct seg6_flavors_info {
>  	/* Flavor operations */
> @@ -411,9 +415,72 @@ static int end_next_csid_core(struct sk_buff *skb, struct seg6_local_lwt *slwt)
>  	return input_action_end_finish(skb, slwt);
>  }
>  
> +static int input_action_end_x_finish(struct sk_buff *skb,
> +				     struct seg6_local_lwt *slwt)
> +{
> +	seg6_lookup_nexthop(skb, &slwt->nh6, 0);
> +
> +	return dst_input(skb);
> +}
> +
> +static int input_action_end_x_core(struct sk_buff *skb,
> +				   struct seg6_local_lwt *slwt)
> +{
> +	struct ipv6_sr_hdr *srh;
> +
> +	srh = get_and_validate_srh(skb);
> +	if (!srh)
> +		goto drop;
> +
> +	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> +
> +	return input_action_end_x_finish(skb, slwt);
> +
> +drop:
> +	kfree_skb(skb);
> +	return -EINVAL;
> +}
> +
> +static int end_x_next_csid_core(struct sk_buff *skb,
> +				struct seg6_local_lwt *slwt)
> +{
> +	const struct seg6_flavors_info *finfo = &slwt->flv_info;
> +	struct in6_addr *daddr = &ipv6_hdr(skb)->daddr;
> +
> +	if (seg6_next_csid_is_arg_zero(daddr, finfo))
> +		return input_action_end_x_core(skb, slwt);
> +
> +	/* update DA */
> +	seg6_next_csid_advance_arg(daddr, finfo);
> +
> +	return input_action_end_x_finish(skb, slwt);
> +}
> +
>  static bool seg6_next_csid_enabled(__u32 fops)
>  {
> -	return fops & BIT(SEG6_LOCAL_FLV_OP_NEXT_CSID);
> +	return fops & SEG6_F_LOCAL_FLV_NEXT_CSID;
> +}
> +
> +/* Processing of SRv6 End, End.X, and End.T behaviors can be extended through
> + * the flavors framework. These behaviors must report the subset of (flavor)
> + * operations they currently implement. In this way, if a user specifies a
> + * flavor combination that is not supported by a given End* behavior, the
> + * kernel refuses to instantiate the tunnel reporting the error.
> + */
> +static int seg6_flv_supp_ops_by_action(int action, __u32 *fops)
> +{
> +	switch (action) {
> +	case SEG6_LOCAL_ACTION_END:
> +		*fops = SEG6_LOCAL_END_FLV_SUPP_OPS;
> +		break;
> +	case SEG6_LOCAL_ACTION_END_X:
> +		*fops = SEG6_LOCAL_END_X_FLV_SUPP_OPS;
> +		break;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +
> +	return 0;
>  }
>  
>  /* We describe the packet state in relation to the absence/presence of the SRH
> @@ -746,21 +813,14 @@ static int input_action_end(struct sk_buff *skb, struct seg6_local_lwt *slwt)
>  /* regular endpoint, and forward to specified nexthop */
>  static int input_action_end_x(struct sk_buff *skb, struct seg6_local_lwt *slwt)
>  {
> -	struct ipv6_sr_hdr *srh;
> -
> -	srh = get_and_validate_srh(skb);
> -	if (!srh)
> -		goto drop;
> -
> -	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> -
> -	seg6_lookup_nexthop(skb, &slwt->nh6, 0);
> +	const struct seg6_flavors_info *finfo = &slwt->flv_info;
> +	__u32 fops = finfo->flv_ops;
>  
> -	return dst_input(skb);
> +	/* check for the presence of NEXT-C-SID since it applies first */
> +	if (seg6_next_csid_enabled(fops))
> +		return end_x_next_csid_core(skb, slwt);
>  
> -drop:
> -	kfree_skb(skb);
> -	return -EINVAL;
> +	return input_action_end_x_core(skb, slwt);
>  }
>  
>  static int input_action_end_t(struct sk_buff *skb, struct seg6_local_lwt *slwt)
> @@ -1404,13 +1464,14 @@ static struct seg6_action_desc seg6_action_table[] = {
>  		.action		= SEG6_LOCAL_ACTION_END,
>  		.attrs		= 0,
>  		.optattrs	= SEG6_F_LOCAL_COUNTERS |
> -				  SEG6_F_ATTR(SEG6_LOCAL_FLAVORS),
> +				  SEG6_F_LOCAL_FLAVORS,
>  		.input		= input_action_end,
>  	},
>  	{
>  		.action		= SEG6_LOCAL_ACTION_END_X,
>  		.attrs		= SEG6_F_ATTR(SEG6_LOCAL_NH6),
> -		.optattrs	= SEG6_F_LOCAL_COUNTERS,
> +		.optattrs	= SEG6_F_LOCAL_COUNTERS |
> +				  SEG6_F_LOCAL_FLAVORS,
>  		.input		= input_action_end_x,
>  	},
>  	{
> @@ -2070,7 +2131,8 @@ static int parse_nla_flavors(struct nlattr **attrs, struct seg6_local_lwt *slwt,
>  {
>  	struct seg6_flavors_info *finfo = &slwt->flv_info;
>  	struct nlattr *tb[SEG6_LOCAL_FLV_MAX + 1];
> -	unsigned long fops;
> +	int action = slwt->action;
> +	__u32 fops, supp_fops;
>  	int rc;
>  
>  	rc = nla_parse_nested_deprecated(tb, SEG6_LOCAL_FLV_MAX,
> @@ -2086,7 +2148,8 @@ static int parse_nla_flavors(struct nlattr **attrs, struct seg6_local_lwt *slwt,
>  		return -EINVAL;
>  
>  	fops = nla_get_u32(tb[SEG6_LOCAL_FLV_OPERATION]);
> -	if (fops & ~SEG6_LOCAL_FLV_SUPP_OPS) {
> +	rc = seg6_flv_supp_ops_by_action(action, &supp_fops);
> +	if (rc < 0 || (fops & ~supp_fops)) {
>  		NL_SET_ERR_MSG(extack, "Unsupported Flavor operation(s)");
>  		return -EOPNOTSUPP;
>  	}
> @@ -2618,6 +2681,11 @@ int __init seg6_local_init(void)
>  	 */
>  	BUILD_BUG_ON(SEG6_LOCAL_MAX + 1 > BITS_PER_TYPE(unsigned long));
>  
> +	/* Check whether the number of defined flavors exceeds the maximum
> +	 * allowed value.
> +	 */
> +	BUILD_BUG_ON(SEG6_LOCAL_FLV_OP_MAX + 1 > BITS_PER_TYPE(__u32));
> +
>  	/* If the default NEXT-C-SID Locator-Block/Node Function lengths (in
>  	 * bits) have been changed with invalid values, kernel build stops
>  	 * here.
> -- 
> 2.20.1
> 

Reviewed-by: Hangbin Liu <liuhangbin@xxxxxxxxx>