[Bug 1621340] Re: [SRU]'multipath -r' causes /dev/mapper/<wwid> being removed

[Chris J Arges]

Hello Liang, or anyone else affected,

Accepted multipath-tools into xenial-proposed. The package will build
now and be available at https://launchpad.net/ubuntu/+source/multipath-
tools/0.5.0+git1.656f8865-5ubuntu2.4 in a few hours, and then in the
-proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to
enable and use -proposed.  Your feedback will aid us getting this update
out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: multipath-tools (Ubuntu Xenial)
       Status: In Progress => Fix Committed

** Tags added: verification-needed

** Changed in: multipath-tools (Ubuntu Yakkety)
       Status: In Progress => Fix Committed

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Title:
  [SRU]'multipath -r' causes /dev/mapper/<wwid> being removed

Status in multipath-tools package in Ubuntu:
  Fix Released
Status in multipath-tools source package in Xenial:
  Fix Committed
Status in multipath-tools source package in Yakkety:
  Fix Committed

Bug description:
  [Impact]

  "multipath -r" causes the /dev/mapper/<wwid> to disappear momentarily,
  which leads to some issue in consumer applications as such OpenStack.

  [Test Case]

   * connect to an multipath iscsi target
   * multipath -r
   * /dev/mapper/<wwid> disappears momentarily

  [Regression Potential]

   * None

  
  "multipath -r" causes the /dev/mapper/<wwid> to disappear momentarily, which leads to some issue in consumer applications as such OpenStack. After some investigation, I found that /dev/mapper/<wwid> was deleted by udev during the reload, and it was re-created soon later by multipathd (livdevmapper code of cause).  Detailed findings are as follows:

  For reload in domap (rename as well),

          case ACT_RELOAD:
                  r = dm_addmap_reload(mpp, params);
                  if (r)
                          r = dm_simplecmd_noflush(DM_DEVICE_RESUME, mpp->alias,
                                                   0, MPATH_UDEV_RELOAD_FLAG);
                  break;

  it passes 0 to dm_simplecmd_noflush as argument for needsync, which
  makes dm_task_set_cookie call being skipped in dm_simplecmd,

          if (udev_wait_flag && !dm_task_set_cookie(dmt, &cookie, ((conf->daemon)? DM_UDEV_DISABLE_LIBRARY_FALLBACK : 0) | udev_flags)) {
                  dm_udev_complete(cookie);
                  goto out;
          }

  because of the short-circuit evaluation. Thus _do_dm_ioctl in
  libdevmapper will add DM_UDEV_DISABLE_DM_RULES_FLAG flag to
  dmi->event_nr, and that will eventually be used in the udev rules
  (55-dm.rules),

  ENV{DM_UDEV_DISABLE_DM_RULES_FLAG}!="1", ENV{DM_NAME}=="?*",
  SYMLINK+="mapper/$env{DM_NAME}"

  Since the DM_UDEV_DISABLE_DM_RULES_FLAG is set, the rule will not
  match. As a result the link is removed.

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