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authorJeff Dike <jdike@addtoit.com>2006-09-29 04:58:46 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-29 12:18:04 -0400
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 107c5e43fa00..142bcb2c7c6a 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -12,6 +12,7 @@
12#include <string.h> 12#include <string.h>
13#include <sys/socket.h> 13#include <sys/socket.h>
14#include <sys/wait.h> 14#include <sys/wait.h>
15#include <sys/time.h>
15#include "user.h" 16#include "user.h"
16#include "user_util.h" 17#include "user_util.h"
17#include "kern_util.h" 18#include "kern_util.h"
@@ -258,3 +259,32 @@ char *split_if_spec(char *str, ...)
258 va_end(ap); 259 va_end(ap);
259 return str; 260 return str;
260} 261}
262
263void random_mac(unsigned char *addr)
264{
265 struct timeval tv;
266 long n;
267 unsigned int seed;
268
269 gettimeofday(&tv, NULL);
270
271 /* Assume that 20 bits of microseconds and 12 bits of the pid are
272 * reasonably unpredictable.
273 */
274 seed = tv.tv_usec | (os_getpid() << 20);
275 srandom(seed);
276
277 /* Don't care about endianness here - switching endianness
278 * just rearranges what are hopefully random numbers.
279 *
280 * Assume that RAND_MAX > 65536, so random is called twice and
281 * we use 16 bits of the result.
282 */
283 n = random();
284 addr[2] = (n >> 8) & 255;
285 addr[3] = n % 255;
286
287 n = random();
288 addr[4] = (n >> 8) & 255;
289 addr[5] = n % 255;
290}