Re: [PATCH mdadm v2 1/2] mdadm: Add --discard option for Create

[Logan Gunthorpe <logang@deltatee.com>]

On 2022-09-14 06:01, Mariusz Tkaczyk wrote:
>>>> As I understand it the offset and size will give the bounds of the
>>>> data region on the disk. Do you not think it works for zoned raid0?  
>>>
>>> mdadm operates on 512B, so using 4K data regions could be destructive.
>>> Also left shift causes that size value is increasing. We can't clear more
>>> that user requested. We need to use 512b sectors as mdadm does.  
>>
>> I don't really follow this.
> 
> I understand that you want left shit is used to round size to data region
> and I assumed that data_region is 4K and that is probably wrong.
> You are right I has no sense, my apologizes.
> 
> Let's imagine that our size is for example, 2687 sectors. Left shit will
> cause that we will get 2751488 and that will be passed as a size to function.
> Similar for data_offset. That is much more than we want to clear.
> Do I miss something? I guess that ioctl operates on sectors too but please
> correct me if that is wrong.

The BLKDISCARD ioctl assumes bytes for the range, not sectors. Though it
does have to be sector aligned.

dv->data_offset is then in sectors, so we shift by 9.

s->size is in KB, so we shift by 10.

Logan