linux-kernel - Re: [PATCH] drivers: target: target_core_mod: use div64_u64

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Message-ID: <52B6AE19.80401@gmail.com>
Date:	Sun, 22 Dec 2013 17:17:13 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	James Hogan <james.hogan@...tec.com>, linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	hare@...e.de, Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH] drivers: target: target_core_mod: use div64_u64_rem()
 instead of operator '%' for u64

On 12/22/2013 10:56 AM, Nicholas A. Bellinger wrote:
> Hi Chen,
> 
> On Sat, 2013-12-21 at 10:08 +0800, Chen Gang wrote:
>> In kernel, need use div64_u64_rem() instead of operator '%' for u64, or
>> can not pass compiling (with allmodconfig under metag):
>>
>>     MODPOST 2909 modules
>>   ERROR: "__umoddi3" [drivers/target/target_core_mod.ko] undefined!
>>
>> Also need u64 type cast for u32 variable multiply u32 variable, or will
>> cause type overflow issue.
>>
>>
>> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
>> ---
>>  drivers/target/target_core_alua.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
> 
> FYI, this unsigned long long division in core_alua_state_lba_dependent()
> was fixed for 32-bit in linux-next >= 12192013 code.
> 

OK, thanks.

The related fix patch changed "start_lba = lba % ..." to "start_lba =
lba / ...", and also assumed "segment_size * segment_mult" is still
within u32 (can not cause type over flow).

I guess the original author already knew about them, and intended to do
like that (if not, please let me know, thanks).


> Regardless, thanks for your patch.
> 

Thank you too.

> --nab
> 
>> diff --git a/drivers/target/target_core_alua.c b/drivers/target/target_core_alua.c
>> index dc0d399..ff2aadc 100644
>> --- a/drivers/target/target_core_alua.c
>> +++ b/drivers/target/target_core_alua.c
>> @@ -489,7 +489,8 @@ static inline int core_alua_state_lba_dependent(
>>  			u64 first_lba = map->lba_map_first_lba;
>>  
>>  			if (segment_mult) {
>> -				start_lba = lba % (segment_size * segment_mult);
>> +				u64 tmp = (u64)segment_size * segment_mult;
>> +				div64_u64_rem(lba, tmp, &start_lba);
>>  				last_lba = first_lba + segment_size - 1;
>>  				if (start_lba >= first_lba &&
>>  				    start_lba <= last_lba) {
> 
> 


-- 
Chen Gang

Open, share and attitude like air, water and life which God blessed
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