[Bug 803554] Re: upgrading to multipath 0.4.9 presents incompatible config file changes

[Peter Petrakis]

Experimenting shows that we can have the older config values side by side
with the new ones. e.g.

...
  prio_callout /sbin/mpath_prio_alua /dev/%n
  prio             alua
...

multipath doesn't have a rigid config file format, it seems to slurp symbols
and then seek the key/value pair out on demand. In doing this, we can safely
downgrade as well.

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https://bugs.launchpad.net/bugs/803554

Title:
  upgrading to multipath 0.4.9 presents incompatible config file changes

Status in “multipath-tools” package in Ubuntu:
  Confirmed

Bug description:
  The priority checkers have been converted from individual binaries
  that callout to dynamically loaded libraries (dlopen). As a result,
  should a circa 0.4.8 config file remain in place, the priority checker
  becomes undefined, as that standalone path checker no longer exists.
  This will effect users who upgrade to Oneiric and users who upgrade
  from lucid to the next LTS.

  One example of the format change is,

  0.4.8:
  prio_callout            "/sbin/mpath_prio_alua /dev/%n"

  0.4.9:
  prio                    alua

  There may be other config file changes, more exploration is needed.

  Here's what the preconfigured, 0.4.9 priority checkers look like.

  # echo 'show config' | multipathd -k | grep 'prio '| sort -u
    prio alua
    prio const
    prio emc
    prio hds
    prio hp_sw
    prio netapp
    prio rdac

  In 0.4.8:
  # echo 'show config' | multipathd -k | grep 'prio_callout'| sort -u
    prio_callout /sbin/mpath_prio_alua /dev/%n
    prio_callout /sbin/mpath_prio_alua %n
    prio_callout /sbin/mpath_prio_emc /dev/%n
    prio_callout /sbin/mpath_prio_hds_modular /dev/%n
    prio_callout /sbin/mpath_prio_hp_sw /dev/%n
    prio_callout /sbin/mpath_prio_netapp /dev/%n
    prio_callout /sbin/mpath_prio_rdac /dev/%n

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