netdev - [PATCH iproute2-next] ip: nexthop: Support 16-bit nexthop weights

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Message-ID: <b5686bb1c47ef3af1d65937cb8f5e378a3abf790.1723829806.git.petrm@nvidia.com>
Date: Fri, 16 Aug 2024 19:38:12 +0200
From: Petr Machata <petrm@...dia.com>
To: David Ahern <dsahern@...nel.org>, Stephen Hemminger
	<stephen@...workplumber.org>, <netdev@...r.kernel.org>
CC: <mlxsw@...dia.com>, Petr Machata <petrm@...dia.com>
Subject: [PATCH iproute2-next] ip: nexthop: Support 16-bit nexthop weights

Two interlinked changes related to the nexthop group management have been
recently merged in kernel commit e96f6fd30eec ("Merge branch
'net-nexthop-increase-weight-to-u16'").

- One of the reserved bytes in struct nexthop_grp was redefined to carry
  high-order bits of the nexthop weight, thus allowing 16-bit nexthop
  weights.

- NHA_OP_FLAGS started getting dumped on nexthop group dump to carry a
  flag, NHA_OP_FLAG_RESP_GRP_RESVD_0, that indicates that reserved fields
  in struct nexthop_grp are zeroed before dumping.

If NHA_OP_FLAG_RESP_GRP_RESVD_0 is given, it is safe to interpret the newly
named nexthop_grp.weight_high as high-order bits of nexthop weight.

Extend ipnexthop to support configuring nexthop weights of up to 65536, and
when dumping, to interpret nexthop_grp.weight_high if safe.

Signed-off-by: Petr Machata <petrm@...dia.com>
---
 ip/ipnexthop.c | 32 +++++++++++++++++++++++++++-----
 ip/nh_common.h |  1 +
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/ip/ipnexthop.c b/ip/ipnexthop.c
index 91b731b0..d5c42936 100644
--- a/ip/ipnexthop.c
+++ b/ip/ipnexthop.c
@@ -234,6 +234,24 @@ static bool __valid_nh_group_attr(const struct rtattr *g_attr)
 	return num && num * sizeof(struct nexthop_grp) == RTA_PAYLOAD(g_attr);
 }
 
+static __u16 nhgrp_weight(__u32 resp_op_flags,
+			  const struct nexthop_grp *nhgrp)
+{
+	__u16 weight = nhgrp->weight_high;
+
+	if (!(resp_op_flags & NHA_OP_FLAG_RESP_GRP_RESVD_0))
+		weight = 0;
+
+	return ((weight << 8) | nhgrp->weight) + 1;
+}
+
+static void nhgrp_set_weight(struct nexthop_grp *nhgrp, __u16 weight)
+{
+	weight--;
+	nhgrp->weight_high = weight >> 8;
+	nhgrp->weight = weight & 0xff;
+}
+
 static void print_nh_group(const struct nh_entry *nhe)
 {
 	int i;
@@ -247,9 +265,10 @@ static void print_nh_group(const struct nh_entry *nhe)
 			print_string(PRINT_FP, NULL, "%s", "/");
 
 		print_uint(PRINT_ANY, "id", "%u", nhe->nh_groups[i].id);
-		if (nhe->nh_groups[i].weight)
-			print_uint(PRINT_ANY, "weight", ",%u",
-				   nhe->nh_groups[i].weight + 1);
+		__u16 weight = nhgrp_weight(nhe->nh_resp_op_flags,
+					    &nhe->nh_groups[i]);
+		if (weight > 1)
+			print_uint(PRINT_ANY, "weight", ",%u", weight);
 
 		close_json_object();
 	}
@@ -507,6 +526,9 @@ static int ipnh_parse_nhmsg(FILE *fp, const struct nhmsg *nhm, int len,
 		parse_nh_group_stats_rta(tb[NHA_GROUP_STATS], nhe);
 	}
 
+	nhe->nh_resp_op_flags =
+		tb[NHA_OP_FLAGS] ? rta_getattr_u32(tb[NHA_OP_FLAGS]) : 0;
+
 	nhe->nh_blackhole = !!tb[NHA_BLACKHOLE];
 	nhe->nh_fdb = !!tb[NHA_FDB];
 
@@ -904,9 +926,9 @@ static int add_nh_group_attr(struct nlmsghdr *n, int maxlen, char *argv)
 			unsigned int w;
 
 			wsep++;
-			if (get_unsigned(&w, wsep, 0) || w == 0 || w > 256)
+			if (get_unsigned(&w, wsep, 0) || w == 0 || w > 65536)
 				invarg("\"weight\" is invalid\n", wsep);
-			grps[i].weight = w - 1;
+			nhgrp_set_weight(&grps[i], w);
 		}
 
 		if (!sep)
diff --git a/ip/nh_common.h b/ip/nh_common.h
index 33b1d847..afbd16b6 100644
--- a/ip/nh_common.h
+++ b/ip/nh_common.h
@@ -25,6 +25,7 @@ struct nh_entry {
 	__u32			nh_id;
 	__u32			nh_oif;
 	__u32			nh_flags;
+	__u32			nh_resp_op_flags;
 	__u16			nh_grp_type;
 	__u8			nh_family;
 	__u8			nh_scope;
-- 
2.45.0