ipv6: sr: add option to control lwtunnel support

This patch adds a new option CONFIG_IPV6_SEG6_LWTUNNEL to enable/disable
support of encapsulation with the lightweight tunnels. When this option
is enabled, CONFIG_LWTUNNEL is automatically selected.

Fix commit 6c8702c6 ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")

Without a proper option to control lwtunnel support for SR-IPv6, if
CONFIG_LWTUNNEL=n then the IPv6 initialization fails as a consequence
of seg6_iptunnel_init() failure with EOPNOTSUPP:

NET: Registered protocol family 10
IPv6: Attempt to unregister permanent protocol 6
IPv6: Attempt to unregister permanent protocol 136
IPv6: Attempt to unregister permanent protocol 17
NET: Unregistered protocol family 10

Tested (compiling, booting, and loading ipv6 module when relevant)
with possible combinations of CONFIG_IPV6={y,m,n},
CONFIG_IPV6_SEG6_LWTUNNEL={y,n} and CONFIG_LWTUNNEL={y,n}.
Reported-by: Lorenzo Colitti <lorenzo@google.com>
Suggested-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/Kconfig

@@ -289,9 +289,20 @@ config IPV6_PIMSM_V2
 	  Support for IPv6 PIM multicast routing protocol PIM-SMv2.
 	  If unsure, say N.
 
+config IPV6_SEG6_LWTUNNEL
+	bool "IPv6: Segment Routing Header encapsulation support"
+	depends on IPV6
+	select LWTUNNEL
+	---help---
+	  Support for encapsulation of packets within an outer IPv6
+	  header and a Segment Routing Header using the lightweight
+	  tunnels mechanism.
+
+	  If unsure, say N.
+
 config IPV6_SEG6_INLINE
 	bool "IPv6: direct Segment Routing Header insertion "
-	depends on IPV6
+	depends on IPV6_SEG6_LWTUNNEL
 	---help---
 	  Support for direct insertion of the Segment Routing Header,
 	  also known as inline mode. Be aware that direct insertion of

net/ipv6/Makefile

@@ -9,7 +9,7 @@ ipv6-objs :=	af_inet6.o anycast.o ip6_output.o ip6_input.o addrconf.o \
 		route.o ip6_fib.o ipv6_sockglue.o ndisc.o udp.o udplite.o \
 		raw.o icmp.o mcast.o reassembly.o tcp_ipv6.o ping.o \
 		exthdrs.o datagram.o ip6_flowlabel.o inet6_connection_sock.o \
-		udp_offload.o seg6.o seg6_iptunnel.o
+		udp_offload.o seg6.o
 
 ipv6-offload :=	ip6_offload.o tcpv6_offload.o exthdrs_offload.o
 
@@ -23,6 +23,8 @@ ipv6-$(CONFIG_IPV6_MULTIPLE_TABLES) += fib6_rules.o
 ipv6-$(CONFIG_PROC_FS) += proc.o
 ipv6-$(CONFIG_SYN_COOKIES) += syncookies.o
 ipv6-$(CONFIG_NETLABEL) += calipso.o
+ipv6-$(CONFIG_IPV6_SEG6_LWTUNNEL) += seg6_iptunnel.o
+ipv6-$(CONFIG_IPV6_SEG6_HMAC) += seg6_hmac.o
 
 ipv6-objs += $(ipv6-y)
 
@@ -44,7 +46,6 @@ obj-$(CONFIG_IPV6_SIT) += sit.o
 obj-$(CONFIG_IPV6_TUNNEL) += ip6_tunnel.o
 obj-$(CONFIG_IPV6_GRE) += ip6_gre.o
 obj-$(CONFIG_IPV6_FOU) += fou6.o
-obj-$(CONFIG_IPV6_SEG6_HMAC) += seg6_hmac.o
 
 obj-y += addrconf_core.o exthdrs_core.o ip6_checksum.o ip6_icmp.o
 obj-$(CONFIG_INET) += output_core.o protocol.o $(ipv6-offload)

net/ipv6/seg6.c

@@ -451,9 +451,11 @@ int __init seg6_init(void)
 	if (err)
 		goto out_unregister_genl;
 
+#ifdef CONFIG_IPV6_SEG6_LWTUNNEL
 	err = seg6_iptunnel_init();
 	if (err)
 		goto out_unregister_pernet;
+#endif
 
 #ifdef CONFIG_IPV6_SEG6_HMAC
 	err = seg6_hmac_init();
@@ -467,10 +469,14 @@ int __init seg6_init(void)
 	return err;
 #ifdef CONFIG_IPV6_SEG6_HMAC
 out_unregister_iptun:
+#ifdef CONFIG_IPV6_SEG6_LWTUNNEL
 	seg6_iptunnel_exit();
 #endif
+#endif
+#ifdef CONFIG_IPV6_SEG6_LWTUNNEL
 out_unregister_pernet:
 	unregister_pernet_subsys(&ip6_segments_ops);
+#endif
 out_unregister_genl:
 	genl_unregister_family(&seg6_genl_family);
 	goto out;
@@ -481,7 +487,9 @@ void seg6_exit(void)
 #ifdef CONFIG_IPV6_SEG6_HMAC
 	seg6_hmac_exit();
 #endif
+#ifdef CONFIG_IPV6_SEG6_LWTUNNEL
 	seg6_iptunnel_exit();
+#endif
 	unregister_pernet_subsys(&ip6_segments_ops);
 	genl_unregister_family(&seg6_genl_family);
 }