Re: [PATCH 1/2] dm: update table type check for dax

From: "Kani, Toshimitsu" <toshi.kani-ZPxbGqLxI0U@public.gmane.org>
To: "snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org"
	<snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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	<dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
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Subject: Re: [PATCH 1/2] dm: update table type check for dax
Date: Tue, 28 Jun 2016 20:23:24 +0000	[thread overview]
Message-ID: <1467145398.3504.439.camel@hpe.com> (raw)
In-Reply-To: <20160628200714.GC8300-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

On Tue, 2016-06-28 at 16:07 -0400, Mike Snitzer wrote:
> On Tue, Jun 28 2016 at  3:37pm -0400,
> Toshi Kani <toshi.kani@hpe.com> wrote:
 :
> You said in the 0th header: "Patch 1 solves an error when lvremove is
> made to a snapshot device."
> 
> I'm not seeing why this patch 1 fixes anything specific to snapshot
> device removal (but I can see why patch 2 makes snapshot creation
> "work").  I'll apply your 2nd patch and see if I can see what you mean.
> 
> I actually see this error, without either of your 2 proposed patches
> applied, when I try to create a snapshot of a DAX capable LV:
> 
> # lvcreate -s -n snap -L 100M pmem/lv
>   device-mapper: reload ioctl on (253:7) failed: Invalid argument
>   Failed to lock logical volume pmem/lv.
>   Aborting. Manual intervention required.
> Jun 28 15:57:28 rhel-storage-02 kernel: device-mapper: ioctl: can't change
> device type after initial table load.

Yes, patch 2 fixes this error.

I have not looked into why lvremove does this, but lvremove to a snapshot
device fails to reload DM table of "<dev>-lvsnap" device (which is marked as
DM_TYPE_BIO_BASED) with DM_TYPE_DAX_BIO_BASED.  Patch 1 fixes this error.  I
think it also generally makes sense to allow this case.

Thanks,
-Toshi
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