Linux: Support wireless IP roaming

This is achieved by checking that the interface is wireless,
IFF_UP and IFF_LOWER_UP are present, but IFF_RUNNING is missing.

This gives exactly the same support as modern NetBSD when carrier
loss is detected, but without the address verifications when the
carrier comes back as that needs to be handled in the kernel.

While IP setup is maintained, other configuration data is discarded.
Note that this should be improved in the future.

Thanks to Boris Krasnovskiy <borkra@gmail.com> for helping with this.

1 files changed, 64 insertions, 18 deletions

diff --git a/src/dhcpcd.c b/src/dhcpcd.c
index 306d1d00..68c82672 100644
--- a/src/dhcpcd.c
+++ b/src/dhcpcd.c
@@ -695,35 +695,82 @@ dhcpcd_reportssid(struct interface *ifp)
 	loginfox("%s: connected to Access Point: %s", ifp->name, pssid);
 }
 
+static void
+dhcpcd_nocarrier_roaming(struct interface *ifp)
+{
+
+	loginfox("%s: carrier lost - roaming", ifp->name);
+
+	/*
+	 * XXX We should pass something like NOCARRIER_ROAMING
+	 * and set if_up=true; ifdown=false; so that the hook scripts
+	 * can make a decision to keep or discard the interface information.
+	 *
+	 * Currently they discard it (no carrier after all) which is
+	 * generally fine as new connections won't work and current
+	 * connections try to chug along as best as.
+	 * dhcpcd has been doing this since NetBSD-7 at least.
+	 *
+	 * However, for slow roaming this is poor for say web browsing
+	 * as new lookups will fail quickly giving a poor user experience.
+	 * We should improve this, but the hooks will require some work first
+	 * as we need to introduce a mechanism to sort interfaces by
+	 * carrier > roaming > nocarrier. Then the hooks know in which
+	 * order to apply their data, if at all.
+	 * This probably should be a user toggle.
+	 */
+	script_runreason(ifp, "NOCARRIER");
+
+#ifdef ARP
+	arp_drop(ifp);
+#endif
+#ifdef INET
+	dhcp_abort(ifp);
+#endif
+#ifdef DHCP6
+	dhcp6_abort(ifp);
+#endif
+}
+
 void
 dhcpcd_handlecarrier(struct interface *ifp, int carrier, unsigned int flags)
 {
 	bool was_link_up = if_is_link_up(ifp);
+	bool was_roaming = if_roaming(ifp);
 
 	ifp->carrier = carrier;
 	ifp->flags = flags;
 
 	if (!if_is_link_up(ifp)) {
-		if (!was_link_up || !ifp->active)
+		if (!ifp->active || (!was_link_up && !was_roaming))
 			return;
-		loginfox("%s: carrier lost", ifp->name);
-		script_runreason(ifp, "NOCARRIER");
+
+		/*
+		 * If the interface is roaming (generally on wireless)
+		 * then while we are not up, we are not down either.
+		 * Preserve the network state until we either disconnect
+		 * or re-connect.
+		 */
+		if (if_roaming(ifp)) {
+			dhcpcd_nocarrier_roaming(ifp);
+			return;
+		}
+
 #ifdef NOCARRIER_PRESERVE_IP
 		if (ifp->flags & IFF_UP &&
 		    !(ifp->options->options & DHCPCD_ANONYMOUS))
 		{
-#ifdef ARP
-			arp_drop(ifp);
-#endif
-#ifdef INET
-			dhcp_abort(ifp);
-#endif
-#ifdef DHCP6
-			dhcp6_abort(ifp);
-#endif
-		} else
+			/* This OS supports the roaming concept on any
+			 * interface. */
+			dhcpcd_nocarrier_roaming(ifp);
+			return;
+		}
 #endif
-			dhcpcd_drop(ifp, 0);
+
+		loginfox("%s: carrier lost", ifp->name);
+		script_runreason(ifp, "NOCARRIER");
+		dhcpcd_drop(ifp, 0);
+
 		if (ifp->options->options & DHCPCD_ANONYMOUS) {
 			bool is_up = ifp->flags & IFF_UP;
 
@@ -734,6 +781,7 @@ dhcpcd_handlecarrier(struct interface *ifp, int carrier, unsigned int flags)
 			if (is_up)
 				if_up(ifp);
 		}
+
 		return;
 	}
 
@@ -774,9 +822,7 @@ dhcpcd_handlecarrier(struct interface *ifp, int carrier, unsigned int flags)
 		    memcmp(ifp->ssid, ossid, ifp->ssid_len)) && ifp->active)
 		{
 			dhcpcd_reportssid(ifp);
-#ifdef NOCARRIER_PRESERVE_IP
 			dhcpcd_drop(ifp, 0);
-#endif
 #ifdef IPV4LL
 			ipv4ll_reset(ifp);
 #endif
@@ -788,17 +834,17 @@ dhcpcd_handlecarrier(struct interface *ifp, int carrier, unsigned int flags)
 
 	dhcpcd_initstate(ifp, 0);
 	script_runreason(ifp, "CARRIER");
+
 #ifdef INET6
-#ifdef NOCARRIER_PRESERVE_IP
 	/* Set any IPv6 Routers we remembered to expire faster than they
 	 * would normally as we maybe on a new network. */
 	ipv6nd_startexpire(ifp);
-#endif
 #ifdef IPV6_MANAGETEMPADDR
 	/* RFC4941 Section 3.5 */
 	ipv6_regentempaddrs(ifp);
 #endif
 #endif
+
 	dhcpcd_startinterface(ifp);
 }