[dm-devel] [PATCH 22/57] multipath: use option '-i' when called from udev

[Benjamin Marzinski]

On Tue, May 03, 2016 at 08:37:08AM +0200, Christophe Varoqui wrote:
>    Ben,
>    does this patch actually break the Red Hat integration ?
>    I'm inclined to merge it if not.

Like we talked about earlier, RedHat uses a completely different
multipath.rules file, which includes some command options that were
NAK'ed for inclusion. We can sort that out. Either we will or we won't
come to an agreement on how multipath should interact with udev. If we
don't we can probably just keep different rules files for the different
distributions. But having a mostly-but-not-quite working version of the
SUSE rules file really benefits nobody. I'm in favor of this going it.

-Ben

>    Thanks,
>    Christophe
>    On Tue, May 3, 2016 at 7:44 AM, Hannes Reinecke <[1]hare at suse.de> wrote:
> 
>      On 05/02/2016 05:31 PM, Benjamin Marzinski wrote:
>      > On Wed, Apr 27, 2016 at 01:10:23PM +0200, Hannes Reinecke wrote:
>      >> multipath should be using the option '-i' to ignore the wwids
>      >> file when called from udev. Otherwise we might run into a race
>      >> condition with systemd and the system might not boot up correctly.
>      >
>      > The race condition being? Are you talking about the udev rules not
>      > claiming a path for multipath, but then having multipathd create a
>      > multipath device using that path? I agree that this can be an issue.
>      > Another way to solve it is to run mutipathd with the -n option in the
>      > initramfs (see commit a8efa5838cf215febd853f282c26af62c0daa862). That
>      > commit solves the race by making mutipathd ignore devices that aren't
>      > already in the wwids file.  This also keeps the initramfs from picking
>      a
>      > different user_friendly_name than will be picked in late boot (but
>      > hopefully that issue has been sorted out by other patches already).
>      >
>      This is in fact SUSE-specific, as we do _not_ require any a-priory
>      configuration. So we will start out with a system without any wwid file,
>      _but_ expect multipath to start up properly.
>      As the wwid file will only be created by multipathd the udev check will
>      always being false, and none of the multipath devices will be created.
>      > I'm not NAKing this. The question of what to do about the differnces
>      in
>      > the distribution's systemd and udev configurations can be hashed out
>      > outside of patch reviewing. I just want to make sure I understand the
>      > race this is solving.
>      >
>      This is in fact a good question.
>      We should be coming up with a common approach which would suit both
>      needs.
> 
>      Cheers,
> 
>      Hannes
>      --
>      Dr. Hannes Reinecke                   zSeries & Storage
>      [2]hare at suse.de                          [3]+49 911 74053 688
>      SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
>      GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
> 
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