[Bug 1556967] [NEW] Support 'multipath -a'

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== 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

** Affects: multipath-tools (Ubuntu)
     Importance: Undecided
     Assignee: Taco Screen team (taco-screen-team)
         Status: New


** Tags: architecture-ppc64le bugnameltc-138917 severity-high targetmilestone-inin1604
-- 
Support 'multipath -a'
https://bugs.launchpad.net/bugs/1556967
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