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

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Message-ID: <CACVXFVOe2juuN=i0PHEHFdcG=Cq2oBL8cB02c2Y_0d29+Z=hnQ@mail.gmail.com>
Date:	Fri, 7 Aug 2015 03:58:29 -0400
From:	Ming Lei <tom.leiming@...il.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...com>,
	Alexander Graf <agraf@...e.com>,
	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 3:48 AM, Christoph Hellwig <hch@....de> wrote:
> On Fri, Aug 07, 2015 at 03:44:58AM -0400, Ming Lei wrote:
>> There shouldn't be any problem about looping over DASP which has
>> 4k sector size. Also for debugging purpose, we can easily emulate 4k
>> sector size disk by QEMU/virtio-blk.
>>
>> We can support 4k sector size on loop for debugging purpose too, but
>> the side effect is that some images can't be loop mounted any more
>> after its secror size is become larger, then people might complain that.
>
> Have you read the patches?
>
> There isn't any change in default behavior, but it allows you to expose
> a non-512 byte sector size _optionally_.  So no images will stop being
> loop mountable, quite to the contrary - you can now loop mount an image
> copied off from the 4k disk which otherwise would have been unusable
> because the file system geometry didn't match what's returned by
> the block layer as the sector size.

I mean the following case:

#losetup -B 4096 /dev/loop0 test.img
#mount /dev/loop0 /mnt
$...
#umount /mnt
#losetup -d /dev/loop0
#losetup /dev/loop0 test1.img
#mount /dev/loop0 /mnt

Then the last mount may fail becase the logical block size is still 4096.

Thanks,
Ming Lei
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