[PATCH] uml: assign random MACs to interfaces if necessary

Assign a random MAC to an ethernet interface if one was not provided on the
command line.  This became pressing when distros started bringing interfaces
up before assigning IPs to them.  The previous pattern of assigning an IP then
bringing it up allowed the MAC to be generated from the first IP assigned.
However, once the thing is up, it's probably a bad idea to change the MAC, so
the MAC stayed initialized to fe:fd:0:0:0:0.

Now, if there is no MAC from the command line, one is generated.  We use the
microseconds from gettimeofday (20 bits), plus the low 12 bits of the pid to
seed the random number generator.  random() is called twice, with 16 bits of
each result used.  I didn't want to have to try to fill in 32 bits optimally
given an arbitrary RAND_MAX, so I just assume that it is greater than 65536
and use 16 bits of each random() return.

There is also a bit of reformatting and whitespace cleanup here.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 14 deletions

diff --git a/arch/um/include/net_user.h b/arch/um/include/net_user.h
index 47ef7cb49a8e..cd19defbfefc 100644
--- a/arch/um/include/net_user.h
+++ b/arch/um/include/net_user.h
@@ -1,4 +1,4 @@
-/* 
+/*
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
  * Licensed under the GPL
  */
@@ -26,8 +26,8 @@ struct net_user_info {
 
 extern void ether_user_init(void *data, void *dev);
 extern void dev_ip_addr(void *d, unsigned char *bin_buf);
-extern void iter_addresses(void *d, void (*cb)(unsigned char *, 
-                                               unsigned char *, void *), 
+extern void iter_addresses(void *d, void (*cb)(unsigned char *,
+                                               unsigned char *, void *),
                            void *arg);
 
 extern void *get_output_buffer(int *len_out);
@@ -51,15 +51,6 @@ extern char *split_if_spec(char *str, ...);
 
 extern int dev_netmask(void *d, void *m);
 
-#endif
+extern void random_mac(unsigned char *addr);
 
-/*
- * Overrides for Emacs so that we follow Linus's tabbing style.
- * Emacs will notice this stuff at the end of the file and automatically
- * adjust the settings for this buffer only.  This must remain at the end
- * of the file.
- * ---------------------------------------------------------------------------
- * Local variables:
- * c-file-style: "linux"
- * End:
- */
+#endif