Wait for link-local address for DHCPv6

dhclient -6 fails if the interface to be configures has no link-local address.
This is especially problematic when only DHCPv6 is used
(e.g., --ip=none --ip6=dhcp), because the wait for a DHCPv4 lease is usually
ample time for the LL address to become available on the IPv6 link.
The LL address must not be tenative.

Therefore, this patch implements waiting for a non-tentative link-local
address in fnet for DHCPv6 configured interfaces.

The command fnet waitll <if> waits for an LL address on the interface <if>.

Currently, the maximum waiting time is 30 seconds,
and the kernel is polled through rtnetlink every 500 milliseconds.
These values seem sufficient for virtual bridged networks,
e.g., libvirt NAT networks.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/fnet/main.c b/src/fnet/main.c
index 890f842f6..3ef500b5e 100644
--- a/src/fnet/main.c
+++ b/src/fnet/main.c
@@ -47,6 +47,7 @@ static void usage(void) {
         printf("\tfnet config mac addr\n");
         printf("\tfnet config ipv6 dev ip\n");
         printf("\tfnet ifup dev\n");
+  printf("\tfnet waitll dev\n");
 }
 
 int main(int argc, char **argv) {
@@ -141,6 +142,9 @@ printf("\n");
         else if (argc == 5 && strcmp(argv[1], "config") == 0 && strcmp(argv[2], "ipv6") == 0) {
                 net_if_ip6(argv[3], argv[4]);
         }
+  else if (argc == 3 && strcmp(argv[1], "waitll") == 0) {
+    net_if_waitll(argv[2]);
+  }
         else {
                 fprintf(stderr, "Error fnet: invalid arguments\n");
                 return 1;