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Date: Thu, 08 Dec 2011 10:25:26 -0500
From: Phillip Susi <psusi@cfl.rr.com>
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To: Karel Zak <kzak@redhat.com>
CC: linux-kernel@vger.kernel.org, Vivek Goyal <vgoyal@redhat.com>,
        Jens Axboe <jaxboe@fusionio.com>
Subject: Re: [PATCH 1/2] Add partition resize function to BLKPG ioctl
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On 12/8/2011 10:16 AM, Karel Zak wrote:
>   Is it safe to alter the partition size in arbitrary way if the
>   partition is used by any process?
>
>   Vivek's BLKPG_EXTEND_PARTITIONV seems more safety, because it extends
>   a partition size only, so all offsets in all running stuff are still
>   valid.
>
>   Maybe you need to check bdevp->bd_openers and returns -EBUSY if you
>   want to alter the begin of the partition.

I disallowed altering the start of the partition ( that would just be 
crazy ), but altering the end has been supported on lvm for years now. 
Ext4 can not perform an online shrink, but btrfs can, and I was able to 
successfully have btrfs shrink the fs and then use BLKPG_RES_PARTITION 
to shrink the partition.