[U-Boot] [PATCH v2] tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed

[U-Boot] [PATCH v2] tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed

[Josh Wu]

As 'time(0) | getpid()' will have a lot of duplicated value. It is not a
expected behavior. We expect different value for the seed when when run
it in many times.

So this patch will left shift the getpid() and add to time(0). That
avoid duplicated value.

Test command is like:
  % RUN=0; while [ $RUN -lt 10000 ]; do
  tools/gen_eth_addr; RUN=$(($RUN+1)); done | sort | uniq | wc -l
  10000

This patch is incorporated with suggestions made by Wolfgang Denk and Andreas
Bie?mann. Thanks them a lot.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
---

Changes in v2:
- left shift and add the getpid() value instead of removing it.

 tools/gen_eth_addr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/gen_eth_addr.c b/tools/gen_eth_addr.c
index bf9d935..5fa3e0c 100644
--- a/tools/gen_eth_addr.c
+++ b/tools/gen_eth_addr.c
@@ -15,7 +15,7 @@ main(int argc, char *argv[])
 {
     unsigned long ethaddr_low, ethaddr_high;
 
-    srand(time(0) | getpid());
+    srand(time(0) + (getpid() << 8));
 
     /*
      * setting the 2nd LSB in the most significant byte of
-- 
1.9.1

[U-Boot] [PATCH v2] tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed

[Andreas Bießmann]

On 09/16/2015 12:21 PM, Josh Wu wrote:
> As 'time(0) | getpid()' will have a lot of duplicated value. It is not a
> expected behavior. We expect different value for the seed when when run

when when ... could be fixed when applied

> it in many times.
> 
> So this patch will left shift the getpid() and add to time(0). That
> avoid duplicated value.
> 
> Test command is like:
>   % RUN=0; while [ $RUN -lt 10000 ]; do
>   tools/gen_eth_addr; RUN=$(($RUN+1)); done | sort | uniq | wc -l
>   10000
> 
> This patch is incorporated with suggestions made by Wolfgang Denk and Andreas
> Bie?mann. Thanks them a lot.
> 
> Signed-off-by: Josh Wu <josh.wu@atmel.com>

Acked-by: Andreas Bie?mann <andreas.devel@googlemail.com>

> ---
> 
> Changes in v2:
> - left shift and add the getpid() value instead of removing it.
> 
>  tools/gen_eth_addr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/gen_eth_addr.c b/tools/gen_eth_addr.c
> index bf9d935..5fa3e0c 100644
> --- a/tools/gen_eth_addr.c
> +++ b/tools/gen_eth_addr.c
> @@ -15,7 +15,7 @@ main(int argc, char *argv[])
>  {
>      unsigned long ethaddr_low, ethaddr_high;
>  
> -    srand(time(0) | getpid());
> +    srand(time(0) + (getpid() << 8));
>  
>      /*
>       * setting the 2nd LSB in the most significant byte of
> 

[U-Boot] [PATCH v2] tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed

[Wolfgang Denk]

Dear Josh Wu,

In message <1442398864-1312-1-git-send-email-josh.wu@atmel.com> you wrote:
> As 'time(0) | getpid()' will have a lot of duplicated value. It is not a
> expected behavior. We expect different value for the seed when when run
> it in many times.
> 
> So this patch will left shift the getpid() and add to time(0). That
> avoid duplicated value.
> 
> Test command is like:
>   % RUN=0; while [ $RUN -lt 10000 ]; do
>   tools/gen_eth_addr; RUN=$(($RUN+1)); done | sort | uniq | wc -l
>   10000
> 
> This patch is incorporated with suggestions made by Wolfgang Denk and Andreas
> Bie?mann. Thanks them a lot.
> 
> Signed-off-by: Josh Wu <josh.wu@atmel.com>
> ---
> 
> Changes in v2:
> - left shift and add the getpid() value instead of removing it.
> 
>  tools/gen_eth_addr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I ran this version through a total of 80,000 runs ; there were no
duplicated addresses found in this test.

Acked-by: Wolfgang Denk <wd@denx.de>
Tested-by: Wolfgang Denk <wd@denx.de>


Thanks!


Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Oh dear, I think you'll find reality's on the blink again."
- Marvin The Paranoid Android

[U-Boot] [U-Boot, v2] tools: gen_eth_addr: add getpid() to time(0) to avoid duplicated seed

[Tom Rini]

On Wed, Sep 16, 2015 at 06:21:04PM +0800, Josh Wu wrote:

> As 'time(0) | getpid()' will have a lot of duplicated value. It is not a
> expected behavior. We expect different value for the seed when when run
> it in many times.
> 
> So this patch will left shift the getpid() and add to time(0). That
> avoid duplicated value.
> 
> Test command is like:
>   % RUN=0; while [ $RUN -lt 10000 ]; do
>   tools/gen_eth_addr; RUN=$(($RUN+1)); done | sort | uniq | wc -l
>   10000
> 
> This patch is incorporated with suggestions made by Wolfgang Denk and Andreas
> Bie?mann. Thanks them a lot.
> 
> Signed-off-by: Josh Wu <josh.wu@atmel.com>
> Acked-by: Andreas Bie?mann <andreas.devel@googlemail.com>
> Acked-by: Wolfgang Denk <wd@denx.de>
> Tested-by: Wolfgang Denk <wd@denx.de>

Applied to u-boot/master, thanks!

-- 
Tom
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