[Bug 1556967] Re: Support 'multipath -a'

[Mathieu Trudel-Lapierre]

** Changed in: multipath-tools (Ubuntu)
     Assignee: Taco Screen team (taco-screen-team) => Mathieu Trudel-Lapierre (mathieu-tl)

** Changed in: multipath-tools (Ubuntu)
       Status: New => Triaged

** Changed in: multipath-tools (Ubuntu)
   Importance: Undecided => High

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Title:
  Support 'multipath -a'

Status in multipath-tools package in Ubuntu:
  Triaged

Bug description:
  == Comment: #0 - Mauricio Faria De Oliveira <mauricfo at br.ibm.com> - 2016-03-14 09:39:20 ==
  Support 'multipath -a' to facilitate post-install migration to multipath environment.

  The attached patch adds 2 upstream commits to support 'multipath -a'.

  Verification:
  --------------

  The new '-a' option:

      # multipath -h 2>&1 | grep -- -a
        multipath [-a|-c|-w|-W] [-d] [-r] [-v lvl] [-p pol] [-b fil] [-q] [dev]
        -a      add a device wwid to the wwids file

  If the device's wwid is not on the wwids file, it's not multipathed:

      # grep -v '^#' /etc/multipath/wwids
      /0QEMU_QEMU_HARDDISK_xenialroot/

      # multipath -v3 | grep wwid
      Mar 14 10:23:10 | wwid 0QEMU_QEMU_HARDDISK_xenialother not in wwids file, skipping sdc

  Now, 'multipath -a' adds it to the wwids file:

      # multipath -a /dev/sdc
      wwid '0QEMU_QEMU_HARDDISK_xenialother' added

      # grep -v '^#' /etc/multipath/wwids 
      /0QEMU_QEMU_HARDDISK_xenialroot/
      /0QEMU_QEMU_HARDDISK_xenialother/

  And it is successfully multipathed:

      # multipath -v3 | grep wwid
      Mar 14 10:24:14 | found wwid 0QEMU_QEMU_HARDDISK_xenialother in wwids file, multipathing sdc
      Mar 14 10:24:14 | Found matching wwid [0QEMU_QEMU_HARDDISK_xenialother] in bindings file. Setting alias to mpathb

  By the way, it works even if the device is locked by a LVM member
  (which doesn't if you try just 'multipath <device>').
  This helps a lot on LVM/multipath scenarios, which had boot issues:

      # dmsetup table | grep VG
      VGsdc-LVsdc: 0 8388608 linear 8:32 2048

      # ls -l /dev/sdc
      brw-rw---- 1 root disk 8, 32 Mar 14 10:28 /dev/sdc

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