nexthop: Extract a common helper for parsing dump attributes

Requests to dump nexthops have many attributes in common with those that
requests to dump buckets of resilient NH groups will have. However, they
have different policies. To allow reuse of this code, extract a
policy-agnostic wrapper out of nh_valid_dump_req(), and convert this
function into a thin wrapper around it.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/nexthop.c

@@ -2015,22 +2015,13 @@ static bool nh_dump_filtered(struct nexthop *nh,
 	return false;
 }
 
-static int nh_valid_dump_req(const struct nlmsghdr *nlh,
-			     struct nh_dump_filter *filter,
-			     struct netlink_callback *cb)
+static int __nh_valid_dump_req(const struct nlmsghdr *nlh, struct nlattr **tb,
+			       struct nh_dump_filter *filter,
+			       struct netlink_ext_ack *extack)
 {
-	struct netlink_ext_ack *extack = cb->extack;
-	struct nlattr *tb[ARRAY_SIZE(rtm_nh_policy_dump)];
 	struct nhmsg *nhm;
-	int err;
 	u32 idx;
 
-	err = nlmsg_parse(nlh, sizeof(*nhm), tb,
-			  ARRAY_SIZE(rtm_nh_policy_dump) - 1,
-			  rtm_nh_policy_dump, NULL);
-	if (err < 0)
-		return err;
-
 	if (tb[NHA_OIF]) {
 		idx = nla_get_u32(tb[NHA_OIF]);
 		if (idx > INT_MAX) {
@@ -2059,6 +2050,22 @@ static int nh_valid_dump_req(const struct nlmsghdr *nlh,
 	return 0;
 }
 
+static int nh_valid_dump_req(const struct nlmsghdr *nlh,
+			     struct nh_dump_filter *filter,
+			     struct netlink_callback *cb)
+{
+	struct nlattr *tb[ARRAY_SIZE(rtm_nh_policy_dump)];
+	int err;
+
+	err = nlmsg_parse(nlh, sizeof(struct nhmsg), tb,
+			  ARRAY_SIZE(rtm_nh_policy_dump) - 1,
+			  rtm_nh_policy_dump, cb->extack);
+	if (err < 0)
+		return err;
+
+	return __nh_valid_dump_req(nlh, tb, filter, cb->extack);
+}
+
 /* rtnl */
 static int rtm_dump_nexthop(struct sk_buff *skb, struct netlink_callback *cb)
 {