From: Roopa Prabhu <roopa@cumulusnetworks.com>
Date: Mon, 27 Apr 2020 13:56:46 -0700
Subject: net: ipv4: add sysctl for nexthop api compatibility mode
Patch-mainline: v5.8-rc1
Git-commit: 4f80116d3df3b23ee4b83ea8557629e1799bc230
References: bsc#1176447

Current route nexthop API maintains user space compatibility
with old route API by default. Dumps and netlink notifications
support both new and old API format. In systems which have
moved to the new API, this compatibility mode cancels some
of the performance benefits provided by the new nexthop API.

This patch adds new sysctl nexthop_compat_mode which is on
by default but provides the ability to turn off compatibility
mode allowing systems to run entirely with the new routing
API. Old route API behaviour and support is not modified by this
sysctl.

Uses a single sysctl to cover both ipv4 and ipv6 following
other sysctls. Covers dumps and delete notifications as
suggested by David Ahern.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 Documentation/networking/ip-sysctl.txt |   12 ++++++++++++
 include/net/netns/ipv4.h               |    2 ++
 net/ipv4/af_inet.c                     |    1 +
 net/ipv4/fib_semantics.c               |    3 +++
 net/ipv4/nexthop.c                     |    5 +++--
 net/ipv4/sysctl_net_ipv4.c             |    9 +++++++++
 net/ipv6/route.c                       |    3 ++-
 7 files changed, 32 insertions(+), 3 deletions(-)

--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1534,6 +1534,18 @@ skip_notify_on_dev_down - BOOLEAN
 	on userspace caches to track link events and evict routes.
 	Default: false (generate message)
 
+nexthop_compat_mode - BOOLEAN
+	New nexthop API provides a means for managing nexthops independent of
+	prefixes. Backwards compatibilty with old route format is enabled by
+	default which means route dumps and notifications contain the new
+	nexthop attribute but also the full, expanded nexthop definition.
+	Further, updates or deletes of a nexthop configuration generate route
+	notifications for each fib entry using the nexthop. Once a system
+	understands the new API, this sysctl can be disabled to achieve full
+	performance benefits of the new API by disabling the nexthop expansion
+	and extraneous notifications.
+	Default: true (backward compat mode)
+
 IPv6 Fragmentation:
 
 ip6frag_high_thresh - INTEGER
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -110,6 +110,8 @@ struct netns_ipv4 {
 	int sysctl_tcp_early_demux;
 	int sysctl_udp_early_demux;
 
+	int sysctl_nexthop_compat_mode;
+
 	int sysctl_fwmark_reflect;
 	int sysctl_tcp_fwmark_accept;
 #ifdef CONFIG_NET_L3_MASTER_DEV
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1831,6 +1831,7 @@ static __net_init int inet_init_net(stru
 	net->ipv4.sysctl_ip_early_demux = 1;
 	net->ipv4.sysctl_udp_early_demux = 1;
 	net->ipv4.sysctl_tcp_early_demux = 1;
+	net->ipv4.sysctl_nexthop_compat_mode = 1;
 #ifdef CONFIG_SYSCTL
 	net->ipv4.sysctl_ip_prot_sock = PROT_SOCK;
 #endif
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1780,6 +1780,8 @@ int fib_dump_info(struct sk_buff *skb, u
 			goto nla_put_failure;
 		if (nexthop_is_blackhole(fi->nh))
 			rtm->rtm_type = RTN_BLACKHOLE;
+		if (!fi->fib_net->ipv4.sysctl_nexthop_compat_mode)
+			goto offload;
 	}
 
 	if (nhs == 1) {
@@ -1805,6 +1807,7 @@ int fib_dump_info(struct sk_buff *skb, u
 			goto nla_put_failure;
 	}
 
+offload:
 	if (fri->offload)
 		rtm->rtm_flags |= RTM_F_OFFLOAD;
 	if (fri->trap)
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -798,7 +798,8 @@ static void __remove_nexthop_fib(struct
 	list_for_each_entry_safe(f6i, tmp, &nh->f6i_list, nh_list) {
 		/* __ip6_del_rt does a release, so do a hold here */
 		fib6_info_hold(f6i);
-		ipv6_stub->ip6_del_rt(net, f6i, false);
+		ipv6_stub->ip6_del_rt(net, f6i,
+				      !net->ipv4.sysctl_nexthop_compat_mode);
 	}
 }
 
@@ -1055,7 +1056,7 @@ out:
 	if (!rc) {
 		nh_base_seq_inc(net);
 		nexthop_notify(RTM_NEWNEXTHOP, new_nh, &cfg->nlinfo);
-		if (replace_notify)
+		if (replace_notify && net->ipv4.sysctl_nexthop_compat_mode)
 			nexthop_replace_notify(net, new_nh, &cfg->nlinfo);
 	}
 
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -723,6 +723,15 @@ static struct ctl_table ipv4_net_table[]
 		.proc_handler   = proc_tcp_early_demux
 	},
 	{
+		.procname       = "nexthop_compat_mode",
+		.data           = &init_net.ipv4.sysctl_nexthop_compat_mode,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+	{
 		.procname	= "ip_default_ttl",
 		.data		= &init_net.ipv4.sysctl_ip_default_ttl,
 		.maxlen		= sizeof(int),
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5561,7 +5561,8 @@ static int rt6_fill_node(struct net *net
 		if (nexthop_is_blackhole(rt->nh))
 			rtm->rtm_type = RTN_BLACKHOLE;
 
-		if (rt6_fill_node_nexthop(skb, rt->nh, &nh_flags) < 0)
+		if (net->ipv4.sysctl_nexthop_compat_mode &&
+		    rt6_fill_node_nexthop(skb, rt->nh, &nh_flags) < 0)
 			goto nla_put_failure;
 
 		rtm->rtm_flags |= nh_flags;