linux-kernel - Re: [PATCH net-next v2 2/2] net: migrate direct users to prandom_u32

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Date:	Wed, 04 Sep 2013 14:58:49 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/2] net: migrate direct users to prandom_u32_max

On 09/04/2013 02:52 PM, Eric Dumazet wrote:
> On Wed, 2013-09-04 at 14:37 +0200, Daniel Borkmann wrote:
>> Users that directly use or reimplement what we have in prandom_u32_max()
>> can be migrated for now to use it directly, so that we can reduce code size
>> and avoid reimplementations. That's obvious, follow-up patches could inspect
>> modulo use cases for possible migration as well.
>>
>> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
>> ---
>>   drivers/net/team/team_mode_random.c | 8 +-------
>>   include/net/red.h                   | 2 +-
>>   net/802/garp.c                      | 3 ++-
>>   net/802/mrp.c                       | 3 ++-
>>   net/packet/af_packet.c              | 2 +-
>>   net/sched/sch_choke.c               | 8 +-------
>>   6 files changed, 8 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/team/team_mode_random.c b/drivers/net/team/team_mode_random.c
>> index 7f032e2..0dbd1eb 100644
>> --- a/drivers/net/team/team_mode_random.c
>> +++ b/drivers/net/team/team_mode_random.c
>> @@ -13,20 +13,14 @@
>>   #include <linux/module.h>
>>   #include <linux/init.h>
>>   #include <linux/skbuff.h>
>> -#include <linux/reciprocal_div.h>
>>   #include <linux/if_team.h>
>>
>> -static u32 random_N(unsigned int N)
>> -{
>> -	return reciprocal_divide(prandom_u32(), N);
>> -}
>> -
>>   static bool rnd_transmit(struct team *team, struct sk_buff *skb)
>>   {
>>   	struct team_port *port;
>>   	int port_index;
>>
>> -	port_index = random_N(team->en_port_count);
>> +	port_index = prandom_u32_max(team->en_port_count - 1);
>
>
> Note the random_N(0) gave 0, while prandom_u32_max(0 - 1) can return any
> number in [0 ... ~0U]

Very true, that was stupid. Thanks for catching!
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