Re: Bug in mtd_speedtest?

[David Lambert <dave@lambsys.com>]

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Artem,
     Please find attached patch.

Regards,

Dave.

On 03/04/2011 12:59 AM, Artem Bityutskiy wrote:
> On Thu, 2011-03-03 at 17:45 -0600, David Lambert wrote:
>> I think I may have found an overflow condition in the speed calculation
>> of mtd_speedtest on some platforms with larger flash partitions:
>>
>> Consider for example if goodebcnt = 15000, and mtd->erasesize =
>> 256*1024, then there is an intermediate product of  3932160000 which
>> results in the sign bit being set on a 32 bit integer. Maybe k should be
>> an unsigned long long?
> Please, just send a patch :-)
>


[-- Attachment #2: patch --]
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Index: mtd_speedtest.c
===================================================================
RCS file: /home/cvsroot/ECMB/src/snapgear/linux-2.6.30.1.x/drivers/mtd/tests/mtd_speedtest.c,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 mtd_speedtest.c
--- mtd_speedtest.c	10 Aug 2009 19:42:00 -0000	1.1.1.1
+++ mtd_speedtest.c	4 Mar 2011 17:51:23 -0000
@@ -281,13 +281,14 @@
 
 static long calc_speed(void)
 {
-	long ms, k, speed;
+	uint64_t k;
+	long ms;
 
-	ms = (finish.tv_sec - start.tv_sec) * 1000 +
-	     (finish.tv_usec - start.tv_usec) / 1000;
-	k = goodebcnt * mtd->erasesize / 1024;
-	speed = (k * 1000) / ms;
-	return speed;
+	ms = (finish.tv_sec - start.tv_sec) * 1000 + /* Time in milli-seconds from start to ...*/
+	     (finish.tv_usec - start.tv_usec) / 1000;	  /* finish */
+	k = (goodebcnt * (mtd->erasesize / 1024) * 1000); /* Number of kBytes transferred * 1000 */
+	do_div(k, ms);	  /* k now contains number of kBytes/second */
+	return k;
 }
 
 static int scan_for_bad_eraseblocks(void)