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Date:	Wed, 28 Nov 2012 07:35:37 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Ryan Wang <openspace.wang@...il.com>,
	Theodore Ts'o <tytso@....edu>,
	Lukáš Czerner <lczerner@...hat.com>,
	linux-ext4@...r.kernel.org, xfs@....sgi.com
Subject: Re: How to run xfstests against multipath disks on SuSE?

On Tue, Nov 27, 2012 at 11:08:30AM -0600, Eric Sandeen wrote:
> On 11/26/12 9:14 PM, Dave Chinner wrote:
> > On Tue, Nov 27, 2012 at 09:20:47AM +0800, Ryan Wang wrote:
> >> 2012/11/26 Theodore Ts'o <tytso@....edu>:
> >>> On Mon, Nov 26, 2012 at 02:43:40PM +0100, Lukáš Czerner wrote:
> >>>>> The I checked the script common.rc, and found that it uses
> >>>>> df to determine the filesystem type and it uses the realpath
> >>>>> "/dev/dm-0" instead of "/dev/mapper/mpatha", while df always
> >>>>> shows "devtmpfs" instead of "ext4" for /dev/dm-0.
> >>>>>
> >>>>> I run "mount" and found that devtmpfs is mount on /dev/ on opensuse
> >>>>> ***by default***. Even though  I run "mount -t btrfs /dev/dm-0 /somedir",
> >>>>> df still showed devtmpfs.
> >>>>>
> >>>>> Any ideas to kick off the xfstests?
> >>>
> >>> At least with the df which ships with Debian Testing, df will display
> >>> the file system in use if it matches the device name which is
> >>> /etc/mtab.  It looks the issue is that mount is canonicalizing the
> >>> device name to be the human friendly version:
> >>>
> >>> # ls -l /dev/mapper/closure-bigscratch
> >>> 0 lrwxrwxrwx 1 root root 7 Nov 16 15:15 /dev/mapper/closure-bigscratch -> ../dm-7
> >>> <tytso.root@...sure> {/home/tytso/bin}, level 2
> >>> # mount /dev/dm-7 /u2
> >>> # df /u2
> >>> Filesystem                     1K-blocks   Used Available Use% Mounted on
> >>> /dev/mapper/closure-bigscratch  52403200 224772  52178428   1% /u2
> >>> # grep /u2 /etc/mtab
> >>> /dev/mapper/closure-bigscratch /u2 xfs rw,relatime,attr2,inode64,noquota 0 0
> >>>
> >>> So the simplest solution is to just use /dev/mapper/mpatha instead of
> >>> insisting on using /dev/dm-0.  That's what I do....
> >>
> >> In xfstests/common.rc, it will use realpath to obtain /dev/dm-0, even if you
> >> specified /dev/mapper/mpatha.
> >> My problem is in SuSE, the devtmpfs is mounted on /dev by default, seems
> >> used by udev. And df reports devtmpfs on /dev/dm-0, instead of ext4.
> > 
> > What version of xfstests are you using? Do you have a
> > "README.device-mapper" file in the base directory? If not, upgrade
> > to the latest version and retry.
> > 
> > $ gl -n 1 -p 0a81886
> > commit 0a818862bb74932e15971ec8bedb55765ec3a3f6
> > Author: Christoph Hellwig <hch@....de>
> > Date:   Wed May 4 16:28:32 2011 +0200
> > 
> >     xfstests: support post-udev device mapper nodes
> > 
> >     Because of udevs complaining device mapper now creates /dev/dm-N as the real
> >     device nodes, and just symlinks the /dev/mapper/ names to it.  This would be
> >     easy if everything used the /dev/mapper clear names, but most system utilities
> >     translate them back to the /dev/mapper/ names and thus confuse various test
> >     cases.  Add support to _is_block_dev to read symlinks, and add documentation
> >     on how to run xfstests on device mapper volumes.
> > 
> >     Signed-off-by: Christoph Hellwig <hch@....de>
> >     Reviewed-by: Alex Elder <aelder@....com>
> > 
> > Cheers,
> > 
> > Dave.
> > 
> 
> Recent "realpath" changes also went in:
> 
> b03c662399956609934ff063e9064e15dc7459ac xfstests: fix to build src/realpath and the correct the existence of target devices
> d5ea873fcbf00b841f0511a26fb341364a5c6425 xfstests: resolve symlinked devices to real paths
> 
> so either of those could have broken and/or fixed it for you :)

Yup, those are almost certainly the patches that broke device mapper
support. There' aren't changes to common.rc, so I didn't notice them.
They basically override the fix that Christoph made to support
/dev/mapper links properly.

I'd suggest a revert is in order, the two patches above were part
of Rich's hovering of old, unreviewed patches. This problem was
already fixed in a different way by Christoph, so adding these
patches was wrong.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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