eth-multiplexer: Generate stable ethernet addresses.

Previously, the ethernet multiplexer generated ethernet addresses for
the virtual interfaces using a pseudo-random number generator.  This
has the downside of generating a new address every time.  Generate
stable pseudo-random addresses instead.

* eth-multiplexer/Makefile (HURDLIBS): Link to libihash.
* eth-multiplexer/ethernet.c (ether_address): New variable.
(get_ethernet_address): New function.
(ethernet_open): Get the ethernet address of the real interface.
* eth-multiplexer/ethernet.h (ether_address): New declaration.
* eth-multiplexer/vdev.c (add_vdev): Compute the ethernet address by
hashing the address of the real interface with the name of the virtual
interface.

4 files changed, 39 insertions, 3 deletions

diff --git a/eth-multiplexer/Makefile b/eth-multiplexer/Makefile
index 35110a80..07f909e7 100644
--- a/eth-multiplexer/Makefile
+++ b/eth-multiplexer/Makefile
@@ -26,7 +26,7 @@ MIGSFLAGS = -imacros $(srcdir)/mig-mutate.h
 device-MIGSFLAGS="-DMACH_PAYLOAD_TO_PORT=ports_payload_get_name"
 OBJS = $(SRCS:.c=.o) $(MIGSTUBS)
 LCLHDRS = ethernet.h util.h vdev.h netfs_impl.h
-HURDLIBS=ports fshelp shouldbeinlibc netfs bpf
+HURDLIBS = ports ihash fshelp shouldbeinlibc netfs bpf
 LDLIBS = -lpthread
 
 CFLAGS += -I$(top_srcdir)/libbpf
diff --git a/eth-multiplexer/ethernet.c b/eth-multiplexer/ethernet.c
index 002f30c2..1f3a57c4 100644
--- a/eth-multiplexer/ethernet.c
+++ b/eth-multiplexer/ethernet.c
@@ -42,6 +42,10 @@ static struct port_info *readpt;
 
 /* Port for writing message to the real network interface. */
 mach_port_t ether_port;
+
+/* The ethernet address of the real network interface.  */
+char ether_address[ETH_ALEN];
+
 /* Port for receiving messages from the interface. */
 static mach_port_t readptname;
 
@@ -102,6 +106,24 @@ int set_promisc (char *dev_name, mach_port_t ether_port, int is_promisc)
   return 0;
 }
 
+static error_t
+get_ethernet_address (mach_port_t port, char *address)
+{
+  error_t err;
+  int net_address[2];
+  size_t count = 2;
+  assert (count * sizeof (int) >= ETH_ALEN);
+
+  err = device_get_status (port, NET_ADDRESS, net_address, &count);
+  if (err)
+    return err;
+
+  net_address[0] = ntohl (net_address[0]);
+  net_address[1] = ntohl (net_address[1]);
+  memcpy (address, net_address, ETH_ALEN);
+  return 0;
+}
+
 int ethernet_open (char *dev_name, device_t master_device,
 		   struct port_bucket *etherport_bucket,
 		   struct port_class *etherreadclass)
@@ -132,6 +154,11 @@ int ethernet_open (char *dev_name, device_t master_device,
     error (2, err, "device_set_filter: %s", dev_name);
 
   set_promisc (dev_name, ether_port, 1);
+
+  err = get_ethernet_address (ether_port, ether_address);
+  if (err)
+    error (2, err, "%s: Cannot get hardware Ethernet address", dev_name);
+
   return 0;
 }
 
diff --git a/eth-multiplexer/ethernet.h b/eth-multiplexer/ethernet.h
index 8efab9b1..a2b2f5ee 100644
--- a/eth-multiplexer/ethernet.h
+++ b/eth-multiplexer/ethernet.h
@@ -23,10 +23,12 @@
 #ifndef ETHERNET_H
 #define ETHERNET_H
 
+#include <mach.h>
+#include <net/if_ether.h>
 #include <netinet/in.h>
-#include <stdlib.h>
 
 extern mach_port_t ether_port;
+extern char ether_address[ETH_ALEN];
 
 int ethernet_open (char *dev_name, device_t master_device,
 		   struct port_bucket *etherport_bucket,
diff --git a/eth-multiplexer/vdev.c b/eth-multiplexer/vdev.c
index e753b85f..47dc8d2d 100644
--- a/eth-multiplexer/vdev.c
+++ b/eth-multiplexer/vdev.c
@@ -28,10 +28,12 @@
 #include <arpa/inet.h>
 #include <stdlib.h>
 #include <error.h>
+#include <hurd/ihash.h>
 
 #include <pthread.h>
 
 #include "vdev.h"
+#include "ethernet.h"
 #include "queue.h"
 #include "bpf_impl.h"
 #include "util.h"
@@ -127,6 +129,7 @@ add_vdev (char *name, int size,
 	  struct port_class *class, struct port_bucket *bucket)
 {
   error_t err;
+  uint32_t hash;
   struct vether_device *vdev;
 
   if (size < sizeof (*vdev))
@@ -143,9 +146,13 @@ add_vdev (char *name, int size,
   vdev->if_header_format = HDR_ETHERNET;
   vdev->if_address_size = ETH_ALEN;
   vdev->if_flags = 0;
+
+  /* Compute a pseudo-random but stable ethernet address.  */
   vdev->if_address[0] = 0x52;
   vdev->if_address[1] = 0x54;
-  *(int *)(vdev->if_address + 2) = random ();
+  hash = hurd_ihash_hash32 (ether_address, ETH_ALEN, 0);
+  hash = hurd_ihash_hash32 (name, strlen (name), hash);
+  memcpy (&vdev->if_address[2], &hash, 4);
 
   queue_init (&vdev->port_list.if_rcv_port_list);
   queue_init (&vdev->port_list.if_snd_port_list);