linux-kernel - Re: [PATCH 0/4] loop: enable different physical blocksizes

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Date:	Fri, 07 Aug 2015 08:46:38 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	Ming Lei <tom.leiming@...il.com>, Alexander Graf <agraf@...e.de>
CC:	Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] loop: enable different physical blocksizes

On 08/07/2015 07:07 AM, Ming Lei wrote:
> On Mon, Aug 3, 2015 at 7:00 PM, Alexander Graf <agraf@...e.de> wrote:
>>

[ .. ]

>>
>> because the guest thinks the disk is formatted with 4k sector size,
>> while mkfs thought it's formatted with 512 byte sector size.
> 
> I am wondering if mkfs is remembering the sector size of actual block
> device, and at least it can't be found by 'dumpe2fs'. And it shouldn't have
> do that, otherwise it isn't flexible. And one fs image often can be looped
> successully by loop because loop's block size is 512.
> 
> That is why I am wondering if we need support other logical block size
> for loop.
> 
If you were to install a bootloader (like lilo or zipl for S/390) it
needs to write the _physical_ block addresses of the kernel and the
initrd. And these do vary, depending in the physical blocksize.
So while the filesystems indeed do not care (all translation is done
in the block driver, not the filesystem), bootloaders most certainly
do.
If you were to create a bootable disk on 4k disks you need this patch.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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