Re: [PATCH 3/7] imsm: PPL support

[Jes Sorensen <Jes.Sorensen@redhat.com>]

Artur Paszkiewicz <artur.paszkiewicz@intel.com> writes:
> On 11/29/2016 12:51 AM, Jes Sorensen wrote:
>>> @@ -3177,6 +3195,9 @@ static void getinfo_super_imsm(struct supertype *st, struct mdinfo *info, char *
>>>  
>>>  		disk = &super->disks->disk;
>>>  		info->data_offset = total_blocks(&super->disks->disk) - reserved;
>>> +		/* mpb anchor sector - see store_imsm_mpb() */
>>> +		info->sb_start = total_blocks(&super->disks->disk) -
>>> +				 ((2 * super->sector_size) >> 9);
>>>  		info->component_size = reserved;
>>>  		info->disk.state  = is_configured(disk) ? (1 << MD_DISK_ACTIVE) : 0;
>>>  		/* we don't change info->disk.raid_disk here because
>> 
>> Hi Artur,
>> 
>> I have been sitting staring at the above for a while, and looking at
>> store_imsm_mpb() it is not clear to me what is meant to happen here.
>> 
>> For 4k sector drives, aren't you pushing back sb_start way further than
>> you are for 512 byte sector drives? Ie. you are subtracting 16 sectors
>> for the 4k drive but only two sectors for the 512 byte sector drive?
>> 
>> Maybe it's because it's Monday or I lost the last of my marbles, but
>> could you possibly enlighten me here please?
>
> Jes,
>
> You read it correctly. The reason for this is that the IMSM anchor is
> located in the second _logical_ sector from the end of the drive. So for
> 4k drives this will be 16 512-byte sectors from the end.

I see, so the IMSM implementation uses 512 byte logical sectors on top
of 4k drives? Could I ask you to add a note explaining this in the code?

Thanks,
Jes