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

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Message-ID: <CACVXFVNB6uGvZmKBa7H7awnb6_MKDFd3qtKWcebLNU=fCQfjqA@mail.gmail.com>
Date:	Fri, 7 Aug 2015 03:23:03 -0400
From:	Ming Lei <tom.leiming@...il.com>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Alexander Graf <agraf@...e.de>, 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 Fri, Aug 7, 2015 at 2:46 AM, Hannes Reinecke <hare@...e.de> wrote:
> 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 there isn't filesystem involved in your case of installing bootloader,
then I am wondering why you don't write the data to the backing block
directly? And why does loop have to be involved in this special case?

> 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.

It it were me, I choose to do that against the disk directly, instead of
using loop, :-)


Thanks,
Ming Lei
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