Re: [PATCH v2 8/8] null_blk: Support configuring the maximum segment size

[Bart Van Assche <bvanassche@acm.org>]

On 11/23/22 17:40, Damien Le Moal wrote:
> On 11/24/22 05:57, Bart Van Assche wrote:
>> +static unsigned int g_max_segment_size = 1UL << 31;
> 
> 1UL is unsigned long be this var is unsigned int. Why not simply use
> UINT_MAX here ? You prefer the 2GB value ? If yes, then may be at least
> change that to "1U << 31", no ?
> 
> [ ... ]
>> @@ -2106,6 +2119,7 @@ static int null_add_dev(struct nullb_device *dev)
>>   	dev->max_sectors = min_t(unsigned int, dev->max_sectors,
>>   				 BLK_DEF_MAX_SECTORS);
>>   	blk_queue_max_hw_sectors(nullb->q, dev->max_sectors);
>> +	blk_queue_max_segment_size(nullb->q, dev->max_segment_size);
> 
> Should we keep the ability to use the kernel default value as the default
> here ?
> E.g.
> 
> 	if (dev->max_segment_size)
> 		blk_queue_max_segment_size(nullb->q,
> 				dev->max_segment_size);
> 
> If yes, then g_max_segment_size initial value should be 0, meaning "kernel
> default".

Hi Damien,

How about changing the default value for g_max_segment_size from
1UL << 31 into BLK_MAX_SEGMENT_SIZE? That will simplify the code and 
also prevents that this patch changes the behavior of the null_blk 
driver if g_max_segment_size is not modified by the user.

Thanks,

Bart.