[Bug 1565817] Re: multipath: LVM physical volumes on individual paths

[Mathieu Trudel-Lapierre]

I sponsored multipath-tools as provided by Mauricio; some comments:

1) for find-multipaths> while sufficient; we set the default as
find_multipaths -- it makes sense for it to always be the default (from
what I recall of my analysis of this some time ago, anyway). Some
installs may not get multipath.conf; or it may be removed by an
unsuspecting admin (or by someone who installed multipath-tools on their
system and perhaps should not have, and then remove the file). It all in
all feels like the least intrusive way to deal with multipath disks on
any random system (but I'm happy to be shown I'm mistaken! :)

As for testing; I have *not* run this in a VM; I felt familiar enough
with the changes to go ahead and upload, however there *should* be some
extensive testing of various multipath scenarios again before release to
iron out any other last-minute bugs. We're *very* close to release by
now, it would be good to not do too many SRU updates to fix things.
Among other things, we'd really benefit from testing with Tore
Anderson's use case, which is different enough from the typical tests
being done on FC and ppc64 to expose some fun bugs.

Finally, all these changes indeed need to go to Debian; we'd really
benefit from reducing our delta even more, such as making sure all the
patches are shared, including find_multipaths if possible.

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https://bugs.launchpad.net/bugs/1565817

Title:
  multipath: LVM physical volumes on individual paths

Status in multipath-tools package in Ubuntu:
  New

Bug description:
  == Comment: #0 - Mauricio Faria De Oliveira - 2016-04-04 10:02:55 ==
  ---Problem Description---
  multipath: LVM physical volumes on individual paths
   
  Contact Information = Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com> / Gabriel Krisman <krisman at linux.vnet.ibm.com> 
   
  This bug reports/patches 2 regressions introduced with multipath-tools 0.5.0+git1.656f8865-5ubuntu1 (see LP 1551952).

  1) The udev rule which removes partition nodes from individual paths
  is not working.

  This happens due to the introduction of the 'udev property blacklisting' feature (which blacklists devices if they don't have certain udev properties defined).
  Because 'multipath -c'  is run at udev rules PROGRAM-rule time, it can't read the required udev properties (defined by sg3-utils udev rules), because they are not yet written to the udev database -- this only happens after the rules finish processing (they would be available at RUN-rule time).
  The solution is to use 'multipath -u', which reads them directly from the udev program environment (and not from the not-yet-updated database) afaik, and makes things work at PROGRAM-rule time.

  This required a change between the local-top/init-top initramfs scripts.
  Since 'multipath -u' checks if multipathd is started, it moved into init-top, so it's started before udev rules are processed.
  While in there, the local-top script is now redundant with other initramfs scripts, and can be removed. See the changelog for details/explanation.

  2) The find_multipath options is no longer enabled by default.

  It's non-default upstream, and with the merge (when the downstream patch was removed), the change/setting was lost. 
  A new patch is introduced which explicitly enables it by the default.

  I'll add more details for the regression #1 shortly.

  Patch attached.

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