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Re: [dm-devel] User friendly names patch.

On Tue, Oct 25, 2005 at 10:41:21AM +0200, Christophe Varoqui wrote:
> > > One of my worry is that /var/lib/multipath/bindings is not available in
> > > early userspace. Is this taken care of. Also remember not relying on
> > > hotplug to execute multipath in early userspace is a redhat choice.
> > > Others strategy may differ.
> > 
> > To make this work seamlessly with early userspace, You would need to add
> > the correct /var/lib/multipath/bindings file to the initrd. The easiest work
> > around to to simply stick the alias for that device in /etc/multipath.conf.
> > 
> > To make this work without editing the initrd or forcing people to have
> > aliases in their config files, you would need to change multipath behavior.
> > Currently, if multipath finds a device with the same wwid and a different
> > alias, it removes the device and recreates it.  If it simply just left the
> > device with the old name, then you would not get the benefit of user friendly
> > names for devices that were started in early userspace, but you would not
> > be any worse off than before. (Well, not quite. A binding would exist for the
> > device in the bindings file, and if on some other boot, that multipath wasn't
> > created in early userspace, when it got created it would use the name from
> > the bindings file). This method would also require a command line option to
> > override the "user_friendly_names" config file option in early userspace.
> > 
> ok,
> let me know what you think of the following early userspace scenario sketch.
> It aleviates the bindings sync issues between early and normal userspace.

It makes sense. I'm not sure that we will be able to get this into the Redhat
initrd (unfortunately, nothing is going in for U3), so we might need to do
things differently.

How about I make the bindings file location configurable, so that everyone
can be happy with the location? I'll leave the default location where it
is now when I send the patch.  If you would like to change it to someplace in
/etc when you commit it, go ahead.

> Pre-requisites :
> - no multipath config or binding files packaged in early userspace
> - move bindings from /var to /etc
> early userspace trace :
> - load storage drivers
> - path nodes are created
> - lookup the rootdev wwid in a config file created at system install time or
>   by init{ramfs,rd} rebuild script
> - exec "multipath $wwid" : the scope limiting is the trick as only root dev
>   map gets created. All defaults will apply : failover policy, etc ...
> - mount /dev/mapper/$wwid
> - pump config and bindings in early userspace namespace
> - umount root fs
> - exec "multipath $wwid" again
> - deduce $alias from {bindings file & $wwid}
> - mount /dev/mapper/$alias
> Regards,
> cvaroqui
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