Generating a random ifid for devices with no L2 header
at all, allowing such devices to take part in IPv6
autoconfiguration. The tuntap driver is one example of
a driver where such an ifid would be useful.

Note that as there is no persistence, new addresses
will be generated every time an interface is brought up:

 # ip -6 addr show dev tun0
 8: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 500
     inet6 fe80::eef2:111c:f270:92ba/64 scope link
        valid_lft forever preferred_lft forever
 # ip link set tun0 down
 # ip link set tun0 up
 # ip -6 addr show dev tun0
 8: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 500
     inet6 fe80::eec0:48d0:6b52:8835/64 scope link
        valid_lft forever preferred_lft forever

Signed-off-by: Bjørn Mork <bjorn@mork.no>
---
I'm planning raw-ip support for the qmi_wwan driver.  And
the feedback from primary users (ModemManager++) is that
a headerless netdev is preferred over a fake ethernet
device. The current plan is to model this after 'tun'
devices, using ARPHRD_NONE as type.

But these devices will need an IPv6 link local address for
full SLAAC support.  I am therefore wondering if an approach
like this patch will be acceptable, or if I should look for
some other solution?



Bjørn


 net/ipv6/addrconf.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d84742f003a9..6cf3cae691a5 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -53,6 +53,7 @@
 #include <linux/if_arp.h>
 #include <linux/if_arcnet.h>
 #include <linux/if_infiniband.h>
+#include <linux/random.h>
 #include <linux/route.h>
 #include <linux/inetdevice.h>
 #include <linux/init.h>

@@ -2026,6 +2027,13 @@ static int addrconf_ifid_ip6tnl(u8 *eui, struct net_device *dev)
        return 0;
 }

+static int addrconf_ifid_random(u8 *eui, struct net_device *dev)
+{
+       get_random_bytes(eui, 8);
+       eui[0] |= 0x02;
+       return 0;
+}
+