Re: Disable IPv6 at startup?

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On 2012-02-16, Grant Edwards <grant.b.edwards@xxxxxxxxx> wrote:

> What's the simplest/best way to "disable" IPv6 at runtime?

Here's my first try at disabling ipv6 at runtime.

It seems to work well enough, but it's not as clean as I had hoped.
Could a patch using this approach be accepted?

Of course I'd clean up the formatting, add a changelog entry and so
on.  I'd also be happy to make this something that has to be enabled
via CDL -- though with the changes shown below, the stack behaves
exactly as before by default. I'm not keen on the "add a globally
visible flag" approach, but it seemed like the only simple solution.

The three things I'm trying to disable are all called via init-table
entries, and AFAICT there's no practical way to remove/skip a table
entry at runtime.

The declaration and definition of the globally visible
cyg_ipv6_runtime_disable flag probably belong somewhere else, but I
haven't figured out where.



Index: net/bsd_tcpip/current/src/sys/kern/uipc_domain.c
===================================================================
--- net/bsd_tcpip/current/src/sys/kern/uipc_domain.c	(revision 6840)
+++ net/bsd_tcpip/current/src/sys/kern/uipc_domain.c	(working copy)
@@ -106,32 +106,42 @@
 			(*pr->pr_init)();
 	}
 	/*
 	 * update global informatio about maximums
 	 */
 	max_hdr = max_linkhdr + max_protohdr;
 	max_datalen = MHLEN - max_hdr;
 	splx(s);
 }
 
+int cyg_ipv6_runtime_disable;
+
 /*
  * Add a new protocol domain to the list of supported domains
  * Note: you cant unload it again because  a socket may be using it.
  * XXX can't fail at this time.
  */
 void
 net_add_domain(void *data)
 {
 	int	s;
 	struct domain *dp;
+        extern struct domain inet6domain;
 
 	dp = (struct domain *)data;
+
+        if (cyg_ipv6_runtime_disable && dp == &inet6domain)
+          {
+            diag_printf("net_add_domain(&inet6domain) -- skipped\n");
+            return;
+          }
+
 	s = splnet();
 	dp->dom_next = domains;
 	domains = dp;
 	splx(s);
 	net_init_domain(dp);
 }
 
 /* ARGSUSED*/
 static void
 domaininit(void *dummy)
Index: net/bsd_tcpip/current/src/sys/netinet6/ip6_input.c
===================================================================
--- net/bsd_tcpip/current/src/sys/netinet6/ip6_input.c	(revision 6840)
+++ net/bsd_tcpip/current/src/sys/netinet6/ip6_input.c	(working copy)
@@ -260,33 +260,41 @@
 add_performance_log(val, addr)
 	unsigned long long val;
 	struct in6_addr *addr;
 {
 	ip6_logentry = (ip6_logentry + 1) % ip6_logsize;
 	ip6_performance_log[ip6_logentry] = val;
 	ip6_performance_addrlog[ip6_logentry] = *addr;
 }
 #endif
 
+extern int cyg_ipv6_runtime_disable;
+
 /*
  * IP6 initialization: fill in IP6 protocol switch table.
  * All protocols not implemented in kernel go to raw IP6 protocol handler.
  */
 void
 ip6_init()
 {
 	struct ip6protosw *pr;
 	int i;
 #ifndef __OpenBSD__
 	struct timeval tv;
 #endif
 
+        if (cyg_ipv6_runtime_disable)
+          {
+            diag_printf("ip6_init() -- skipping\n");
+            return;
+          }
+
 #ifdef RADIX_ART
 	rt_tables[AF_INET6]->rnh_addrsize = sizeof(struct in6_addr);
 #endif
 
 #ifdef DIAGNOSTIC
 	if (sizeof(struct protosw) != sizeof(struct ip6protosw))
 		panic("sizeof(protosw) != sizeof(ip6protosw)");
 #endif
 	pr = (struct ip6protosw *)pffindproto(PF_INET6, IPPROTO_RAW, SOCK_RAW);
 	if (pr == 0)
@@ -338,20 +346,26 @@
 #endif
 }
 
 static void
 ip6_init2(dummy)
 	void *dummy;
 {
 #if defined(__bsdi__) && _BSDI_VERSION < 199802
 	struct ifnet *loifp = &loif;
 #endif
+ 
+        if (cyg_ipv6_runtime_disable)
+          {
+            diag_printf("ip6_init2() -- skipping\n");
+            return;
+          }
 
 	/*
 	 * to route local address of p2p link to loopback,
 	 * assign loopback address first.
 	 */
 #ifdef __bsdi__
 	in6_ifattach(loifp, NULL);
 #elif defined(__OpenBSD__)
 	in6_ifattach(lo0ifp, NULL);
 #else




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