[dm-devel] [PATCH 08/18] Fix issues with user_friendly_names initramfs bindings

[Benjamin Marzinski]

On Thu, Oct 15, 2015 at 10:52:31AM +0200, Hannes Reinecke wrote:
> On 10/08/2015 09:44 PM, Benjamin Marzinski wrote:
> > Multipath has an issue with user_friendly_names set in the initramfs.
> > If the bindings are in the initramfs bindings file, it will create them,
> > and it may use bindings that are different than the ones in the regular
> > file system.  Once multipathd starts up in the regular file system, it
> > will try to register the existing bindings, but that may (and in many
> > cases, is likely to) fail. If it can't reanme it, will pick a new
> > binding. Since when multipathd starts discovering the existing devices,
> > it obviously doesn't know all of the existing devices yet, it may very
> > well pick a binding that's already in use by a device that it hasn't
> > discovered yet. In this case multipath will be unable to rename the
> > device to the new binding. Unfortunately, if it fails the rename, it
> > never resets the alias of the device stored in the mpvec to current
> > alias of the actual dm device. So multipath will have devices in the
> > mpvec where the alias and the wwid don't match the actual dm devices
> > that exist.  This can cause all sorts of problems.
> > 
> > This patch does two things to deal with this.  First, it makes sure that
> > if the rename fails, the device will reset its alias to the one that it
> > currently has.
> > 
> > Second, it adds a new option to help avoid the problem in the first
> > place.  There actually already is a solution to this issue. If
> > multipathd is started with -B, it makes the bindings file read-only. If
> > multipathd is started this way in the initramfs, it will never make new
> > bindings for a device. If the device doesn't already have a binding, it
> > will simply be named with its wwid. The problem with this method is that
> > AFAICT it causes a maintenance problem with dracut.  At least on RedHat,
> > dracut is simply copying the regular multipathd.service file into the
> > initramfs. I don't see a way in multipathd.service to only start
> > multipathd with the -B option in the initramfs (If there is a way, I'd
> > be happy to use that). So, the only alternative that lets us use -B is
> > to have a separate multipathd.service file that dracut uses for the
> > initramfs.  This seems like more work than it's worth.
> > 
> > Instead, this patch pulls some code from systemd to detect if multipathd
> > is running in the initramfs.  If it is, and if new_bindings_in_boot is
> > not set, multipathd will set the bindings file to read-only, just like
> > the -B option does.
> > 
> > Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> 
> Please split off this patch. The first issue is a real fix, it should
> really be a separate patch.
> 
> For the second one it actually quite simple to inject a different
> service file for dracut (I did that actually in our dracut package).
> So I'd rather see this happening instead of second-guessing by looking
> at magic files. Which will fail for anyone _not_ using dracut.

Fine. I'd rather only manage one multipathd.service file, but your point
that my solution is dracut specific is fair.

-Ben
 
> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke		      zSeries & Storage
> hare at suse.de			      +49 911 74053 688
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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> 
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