New pref-src & src-prefix actions in install filter

The purpose is to override *locally*:
- RTA_SRC ('from' option in ip-route)
- RTA_PREFSRC ('src' in ip-route)

For RTA_PREFSRC, there is a pull request that could replace this at
  https://github.com/jech/babeld/pull/18
But it looks better to do it our way.

TODO: documentation

configuration.c

@@ -469,6 +469,15 @@ parse_filter(int c, gnc_t gnc, void *closure, struct filter **filter_return)
             if(table <= 0 || table > INFINITY)
                 goto error;
             filter->action.table = table;
+        } else if(strcmp(token, "pref-src") == 0) {
+            int af;
+            c = getip(c, &filter->action.pref_src, &af, gnc, closure);
+            if(c < -1)
+                goto error;
+            if(filter->af == AF_UNSPEC)
+                filter->af = af;
+            else if(filter->af != af)
+                goto error;
         } else {
             goto error;
         }

configuration.h

@@ -34,6 +34,7 @@ struct filter_result {
     unsigned char *src_prefix;
     unsigned char src_plen;
     unsigned int table;
+    unsigned char *pref_src;
 };
 
 struct filter {

disambiguation.c

@@ -36,6 +36,7 @@ THE SOFTWARE.
 #include "neighbour.h"
 #include "rule.h"
 #include "disambiguation.h"
+#include "configuration.h"
 
 struct zone {
     const unsigned char *dst_prefix;
@@ -211,38 +212,57 @@ is_installed(struct zone *zone)
                              zone->src_prefix, zone->src_plen) != NULL;
 }
 
+static const unsigned char *install_zone(struct zone *zone)
+{
+    struct filter_result filter_result;
+
+    if(INFINITY == install_filter(zone->dst_prefix, zone->dst_plen,
+                                  zone->src_prefix, zone->src_plen,
+                                  &filter_result))
+      return NULL;
+
+    if(filter_result.src_prefix) {
+      zone->src_prefix = filter_result.src_prefix;
+      zone->src_plen = filter_result.src_plen;
+    }
+    return filter_result.pref_src;
+}
+
 static int
-add_route(const struct zone *zone, const struct babel_route *route)
+add_route(struct zone *zone, const struct babel_route *route)
 {
+    const unsigned char *pref_src = install_zone(zone);
     int table = find_table(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen);
     return kernel_route(ROUTE_ADD, table, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop,
                         route->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0, 0);
 }
 
 static int
-del_route(const struct zone *zone, const struct babel_route *route)
+del_route(struct zone *zone, const struct babel_route *route)
 {
+    const unsigned char *pref_src = install_zone(zone);
     int table = find_table(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen);
     return kernel_route(ROUTE_FLUSH, table, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop,
                         route->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0, 0);
 }
 
 static int
-chg_route(const struct zone *zone, const struct babel_route *old,
+chg_route(struct zone *zone, const struct babel_route *old,
           const struct babel_route *new)
 {
+    const unsigned char *pref_src = install_zone(zone);
     int table = find_table(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen);
     return kernel_route(ROUTE_MODIFY, table, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         old->nexthop, old->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(old)),
                         new->nexthop, new->neigh->ifp->ifindex,
@@ -250,13 +270,14 @@ chg_route(const struct zone *zone, const struct babel_route *old,
 }
 
 static int
-chg_route_metric(const struct zone *zone, const struct babel_route *route,
+chg_route_metric(struct zone *zone, const struct babel_route *route,
                  int old_metric, int new_metric)
 {
+    const unsigned char *pref_src = install_zone(zone);
     int table = find_table(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen);
     return kernel_route(ROUTE_MODIFY, table, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop, route->neigh->ifp->ifindex,
                         old_metric,
                         route->nexthop, route->neigh->ifp->ifindex,

kernel.h

@@ -94,6 +94,7 @@ int kernel_disambiguate(int v4);
 int kernel_route(int operation, int table,
                  const unsigned char *dest, unsigned short plen,
                  const unsigned char *src, unsigned short src_plen,
+                 const unsigned char *pref_src,
                  const unsigned char *gate, int ifindex, unsigned int metric,
                  const unsigned char *newgate, int newifindex,
                  unsigned int newmetric, int newtable);

kernel_netlink.c

@@ -927,6 +927,7 @@ int
 kernel_route(int operation, int table,
              const unsigned char *dest, unsigned short plen,
              const unsigned char *src, unsigned short src_plen,
+             const unsigned char *pref_src,
              const unsigned char *gate, int ifindex, unsigned int metric,
              const unsigned char *newgate, int newifindex,
              unsigned int newmetric, int newtable)
@@ -980,11 +981,11 @@ kernel_route(int operation, int table,
            stick with the naive approach, and hope that the window is
            small enough to be negligible. */
         kernel_route(ROUTE_FLUSH, table, dest, plen,
-                     src, src_plen,
+                     src, src_plen, pref_src,
                      gate, ifindex, metric,
                      NULL, 0, 0, 0);
         rc = kernel_route(ROUTE_ADD, newtable, dest, plen,
-                          src, src_plen,
+                          src, src_plen, pref_src,
                           newgate, newifindex, newmetric,
                           NULL, 0, 0, 0);
         if(rc < 0) {
@@ -1067,17 +1068,24 @@ kernel_route(int operation, int table,
         rta->rta_type = RTA_OIF;
         *(int*)RTA_DATA(rta) = ifindex;
 
-        if(ipv4) {
-            rta = RTA_NEXT(rta, len);
-            rta->rta_len = RTA_LENGTH(sizeof(struct in_addr));
-            rta->rta_type = RTA_GATEWAY;
-            memcpy(RTA_DATA(rta), gate + 12, sizeof(struct in_addr));
-        } else {
-            rta = RTA_NEXT(rta, len);
-            rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr));
-            rta->rta_type = RTA_GATEWAY;
-            memcpy(RTA_DATA(rta), gate, sizeof(struct in6_addr));
-        }
+#define ADD_IPARG(type, addr) \
+        do if(ipv4) { \
+            rta = RTA_NEXT(rta, len); \
+            rta->rta_len = RTA_LENGTH(sizeof(struct in_addr)); \
+            rta->rta_type = type; \
+            memcpy(RTA_DATA(rta), addr + 12, sizeof(struct in_addr)); \
+        } else { \
+            rta = RTA_NEXT(rta, len); \
+            rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr)); \
+            rta->rta_type = type; \
+            memcpy(RTA_DATA(rta), addr, sizeof(struct in6_addr)); \
+        } while (0)
+
+        ADD_IPARG(RTA_GATEWAY, gate);
+        if(pref_src)
+            ADD_IPARG(RTA_PREFSRC, pref_src);
+
+#undef ADD_IPARG
     } else {
         *(int*)RTA_DATA(rta) = -1;
     }

kernel_socket.c

@@ -406,6 +406,7 @@ int
 kernel_route(int operation, int table,
              const unsigned char *dest, unsigned short plen,
              const unsigned char *src, unsigned short src_plen,
+             const unsigned char *pref_src,
              const unsigned char *gate, int ifindex, unsigned int metric,
              const unsigned char *newgate, int newifindex,
              unsigned int newmetric, int newtable)
@@ -422,8 +423,9 @@ kernel_route(int operation, int table,
         {{{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
             0x00, 0x00, 0x00, 0x00, 0x7f, 0x00, 0x00, 0x01 }}};
 
-    /* Source-specific routes are not implemented yet for BSD. */
-    if(!is_default(src, src_plen)) {
+    /* Source-specific routes & preferred source IPs
+     * are not implemented yet for BSD. */
+    if((!is_default(src, src_plen)) || pref_src) {
         errno = ENOSYS;
         return -1;
     }