Subject: Re: [PATCH net-next] bonding: Use do_div to divide 64 bit numbers

From: Nikolay Aleksandrov <[email-masked]>
Date: Thu, 23 Jan 2014 22:18:24 +0100

On 01/23/2014 09:44 PM, Nikolay Aleksandrov wrote:
> On 01/23/2014 07:47 PM, Zoltan Kiss wrote:
>> Nikolay Aleksandrov's recent bonding option API changes (25a9b54a and e4994612)
>> introduced u64 as the type of downdelay and updelay. On 32 bit the division and
>> modulo operations cause compile errors:
>>
>> ERROR: "__udivdi3" [drivers/net/bonding/bonding.ko] undefined!
>> ERROR: "__umoddi3" [drivers/net/bonding/bonding.ko] undefined!
>>
>> This patch use the do_div macro, which guaranteed to do the right thing.
>>
>> Signed-off-by: Zoltan Kiss <[email-masked]>
>> ---
>>  drivers/net/bonding/bond_options.c |   19 +++++++++++--------
>>  1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
>> index 4cee04a..4f94907 100644
>> --- a/drivers/net/bonding/bond_options.c
>> +++ b/drivers/net/bonding/bond_options.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/rcupdate.h>
>>  #include <linux/ctype.h>
>>  #include <linux/inet.h>
>> +#include <asm/div64.h>
>>  #include "bonding.h"
>>  
>>  static struct bond_opt_value bond_mode_tbl[] = {
>> @@ -727,19 +728,20 @@ int bond_option_miimon_set(struct bonding *bond, struct bond_opt_value *newval)
>>  
>>  int bond_option_updelay_set(struct bonding *bond, struct bond_opt_value *newval)
>>  {
>> +	u64 quotient = newval->value;
>> +	u64 remainder = do_div(quotient, bond->params.miimon);
> Hi Zoltan,
> Thanks for fixing this, a few comments though:
> bond->params.miimon can be 0 here that's why there's a check afterwards,
> also please separate the local variable definitions from the body with a
> new line.
> The same applies for downdelay.
> 
> Nik
In fact since we don't need the u64 and newval->value is limited to
INT_MAX, can't we simply cast it to (int) and avoid the do_div entirely ?

>>  	if (!bond->params.miimon) {
>>  		pr_err("%s: Unable to set up delay as MII monitoring is disabled\n",
>>  		       bond->dev->name);
>>  		return -EPERM;
>>  	}
>> -	if ((newval->value % bond->params.miimon) != 0) {
>> +	if (remainder != 0) {
>>  		pr_warn("%s: Warning: up delay (%llu) is not a multiple of miimon (%d), updelay rounded to %llu ms\n",
>>  			bond->dev->name, newval->value,
>>  			bond->params.miimon,
>> -			(newval->value / bond->params.miimon) *
>> -			bond->params.miimon);
>> +			quotient * bond->params.miimon);
>>  	}
>> -	bond->params.updelay = newval->value / bond->params.miimon;
>> +	bond->params.updelay = quotient;
>>  	pr_info("%s: Setting up delay to %d.\n",
>>  		bond->dev->name,
>>  		bond->params.updelay * bond->params.miimon);
>> @@ -750,19 +752,20 @@ int bond_option_updelay_set(struct bonding *bond, struct bond_opt_value *newval)
>>  int bond_option_downdelay_set(struct bonding *bond,
>>  			      struct bond_opt_value *newval)
>>  {
>> +	u64 quotient = newval->value;
>> +	u64 remainder = do_div(quotient, bond->params.miimon);
>>  	if (!bond->params.miimon) {
>>  		pr_err("%s: Unable to set down delay as MII monitoring is disabled\n",
>>  		       bond->dev->name);
>>  		return -EPERM;
>>  	}
>> -	if ((newval->value % bond->params.miimon) != 0) {
>> +	if (remainder != 0) {
>>  		pr_warn("%s: Warning: down delay (%llu) is not a multiple of miimon (%d), delay rounded to %llu ms\n",
>>  			bond->dev->name, newval->value,
>>  			bond->params.miimon,
>> -			(newval->value / bond->params.miimon) *
>> -			bond->params.miimon);
>> +			quotient * bond->params.miimon);
>>  	}
>> -	bond->params.downdelay = newval->value / bond->params.miimon;
>> +	bond->params.downdelay = quotient;
>>  	pr_info("%s: Setting down delay to %d.\n",
>>  		bond->dev->name,
>>  		bond->params.downdelay * bond->params.miimon);
>>
> 
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