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authorJeff Dike <jdike@addtoit.com>2006-09-29 01:58:46 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-29 09:18:04 -0700
commitf3e7ed2b617824f79d1223f37430ccffae59e5b8 (patch)
tree629961c5ea7aa34675c8a6760e88e3957099f0af /arch/um/drivers/net_user.c
parent3b08606dc2991bcdab14139efd9ed9d492f5f901 (diff)
[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>
Diffstat (limited to 'arch/um/drivers/net_user.c')
-rw-r--r--arch/um/drivers/net_user.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/arch/um/drivers/net_user.c b/arch/um/drivers/net_user.c
index 107c5e43fa0..142bcb2c7c6 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -12,6 +12,7 @@
#include <string.h>
#include <sys/socket.h>
#include <sys/wait.h>
+#include <sys/time.h>
#include "user.h"
#include "user_util.h"
#include "kern_util.h"
@@ -258,3 +259,32 @@ char *split_if_spec(char *str, ...)
va_end(ap);
return str;
}
+
+void random_mac(unsigned char *addr)
+{
+ struct timeval tv;
+ long n;
+ unsigned int seed;
+
+ gettimeofday(&tv, NULL);
+
+ /* Assume that 20 bits of microseconds and 12 bits of the pid are
+ * reasonably unpredictable.
+ */
+ seed = tv.tv_usec | (os_getpid() << 20);
+ srandom(seed);
+
+ /* Don't care about endianness here - switching endianness
+ * just rearranges what are hopefully random numbers.
+ *
+ * Assume that RAND_MAX > 65536, so random is called twice and
+ * we use 16 bits of the result.
+ */
+ n = random();
+ addr[2] = (n >> 8) & 255;
+ addr[3] = n % 255;
+
+ n = random();
+ addr[4] = (n >> 8) & 255;
+ addr[5] = n % 255;
+}