Extend --ra-param mtu: field to allow an interface name.

CHANGELOG

@@ -103,7 +103,12 @@ version 2.77
             presence of the --bogus-priv flag. Thanks to
 	    Vladislav Grishenko for the patch.
 
-	
+	    Extend --ra-param mtu: field to allow an interface name.
+	    This allows the MTU of a WAN interface to be advertised on
+   	    the internal interfaces of a router. Thanks to
+	    Vladislav Grishenko for the patch.
+
+
 version 2.76
             Include 0.0.0.0/8 in DNS rebind checks. This range 
 	    translates to hosts on  the local network, or, at 

man/dnsmasq.8

@@ -1776,7 +1776,7 @@ the relevant link-local address of the machine running dnsmasq is sent
 as recursive DNS server. If provided, the DHCPv6 options dns-server and
 domain-search are used for the DNS server (RDNSS) and the domain search list (DNSSL).
 .TP
-.B --ra-param=<interface>,[mtu:<integer>|off,][high,|low,]<ra-interval>[,<router lifetime>]
+.B --ra-param=<interface>,[mtu:<integer>|<interface>|off,][high,|low,]<ra-interval>[,<router lifetime>]
 Set non-default values for router advertisements sent via an
 interface. The priority field for the router may be altered from the
 default of medium with eg
@@ -1788,7 +1788,11 @@ a router to advertise prefixes but not a route via itself.
 .B --ra-parm=eth0,0,0
 (A value of zero for the interval means the default value.) All four parameters may be set at once.
 .B --ra-param=eth0,mtu:1280,low,60,1200
+
 The interface field may include a wildcard.
+
+The mtu: parameter may be an arbitrary interface name, in which case the MTU value for that interface is used. This is useful
+for (eg) advertising the MTU of a WAN interface on the other interfaces of a router.
 .TP
 .B --dhcp-reply-delay=[tag:<tag>,]<integer>
 Delays sending DHCPOFFER and proxydhcp replies for at least the specified number of seconds.

man/fr/dnsmasq.8

@@ -1756,7 +1756,7 @@ dnsmasq est spécifiée comme DNS récursif. Si elles sont fournies, les
 options dns-server et domain-search sont utilisées respectivement pour RDNSS et
 DNSSL.
 .TP
-.B --ra-param=<interface>,[mtu:<valeur>|off,][high,|low,]<intervalle d'annonce routeur>[,<durée de vie route>]
+.B --ra-param=<interface>,[mtu:<valeur>|<interface>|off,][high,|low,]<intervalle d'annonce routeur>[,<durée de vie route>]
 Configure pour une interface donnée des valeurs pour les annonces routeurs
 différentes des valeurs par défaut. La valeur par défaut du champ priorité
 pour le routeur peut-être changée de "medium" (moyen) à "high" (haute) ou

src/dnsmasq.h

@@ -841,6 +841,7 @@ struct prefix_class {
 
 struct ra_interface {
   char *name;
+  char *mtu_name;
   int interval, lifetime, prio, mtu;
   struct ra_interface *next;
 };

src/option.c

@@ -488,7 +488,7 @@ static struct {
 #ifdef OPTION6_PREFIX_CLASS 
   { LOPT_PREF_CLSS, ARG_DUP, "set:tag,<class>", gettext_noop("Specify DHCPv6 prefix class"), NULL },
 #endif
-  { LOPT_RA_PARAM, ARG_DUP, "<iface>,[mtu:<value>|off,][<prio>,]<intval>[,<lifetime>]", gettext_noop("Set MTU, priority, resend-interval and router-lifetime"), NULL },
+  { LOPT_RA_PARAM, ARG_DUP, "<iface>,[mtu:<value>|<interface>|off,][<prio>,]<intval>[,<lifetime>]", gettext_noop("Set MTU, priority, resend-interval and router-lifetime"), NULL },
   { LOPT_QUIET_DHCP, OPT_QUIET_DHCP, NULL, gettext_noop("Do not log routine DHCP."), NULL },
   { LOPT_QUIET_DHCP6, OPT_QUIET_DHCP6, NULL, gettext_noop("Do not log routine DHCPv6."), NULL },
   { LOPT_QUIET_RA, OPT_QUIET_RA, NULL, gettext_noop("Do not log RA."), NULL },
@@ -3707,6 +3707,7 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	  new->lifetime = -1;
 	  new->prio = 0;
 	  new->mtu = 0;
+	  new->mtu_name = NULL;
 	  new->name = opt_string_alloc(arg);
 	  if (strcasestr(comma, "mtu:") == comma)
 	    {
@@ -3715,7 +3716,9 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	        goto err;
 	      if (!strcasecmp(arg, "off"))
 	        new->mtu = -1;
-	      else if (!atoi_check(arg, &new->mtu) || new->mtu < 1280)
+	      else if (!atoi_check(arg, &new->mtu))
+	        new->mtu_name = opt_string_alloc(arg);
+	      else if (new->mtu < 1280)
 	        goto err;
 	    }
 	  if (strcasestr(comma, "high") == comma || strcasestr(comma, "low") == comma)

src/radv.c

@@ -408,7 +408,8 @@ static void send_ra_alias(time_t now, int iface, char *iface_name, struct in6_ad
      available from SIOCGIFMTU */
   if (mtu == 0)
     {
-      sprintf(daemon->namebuff, "/proc/sys/net/ipv6/conf/%s/mtu", iface_name);
+      char *mtu_name = ra_param ? ra_param->mtu_name : NULL;
+      sprintf(daemon->namebuff, "/proc/sys/net/ipv6/conf/%s/mtu", mtu_name ? : iface_name);
       if ((f = fopen(daemon->namebuff, "r")))
         {
           if (fgets(daemon->namebuff, MAXDNAME, f))