[Bug 1578654] Re: multipath does not set fiberchannel params correctly

[Chris J Arges]

** Also affects: multipath-tools (Ubuntu Trusty)
   Importance: Undecided
       Status: New

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Title:
  multipath does not set fiberchannel params correctly

Status in multipath-tools package in Ubuntu:
  Fix Released
Status in multipath-tools source package in Trusty:
  New

Bug description:
  [Impact]

  multipath has configuration settings such as "dev_loss_tmo" and
  "fast_io_fail_tmo" which multipath uses to change the underlying
  device's parameters.  However, it fails to set any of them; it is
  trying to write the parameters to the sysfs device's directory,
  instead of the attribute file inside the dir.  This results in
  configuration parameters that the user provides not having any effect
  at all, and no error logs being shown.

  The commit 050b24b33d3c60e29f7820d2fb75e84a9edde528 ("multipath: fix
  setting sysfs fc timeout parameters") from upstream multipath-tools
  fixes the bug by actually using the sysfs attribute files, instead of
  the sysfs device directory.

  [Test Case]

  A trusty system with fiberchannel drive(s), with multiple redundant
  paths to the drive(s), is required.  The FC drives must be configured
  and appear in the system, i.e. as /dev/sd* or similar node that
  multipath scans.

  Note that multipath-tools in trusty does not (yet) support setting
  sysfs attributes for iSCSI devices, only FC.

  Check the current value, replace 'rport-N:N-N' with the rport number,
  e.g. 'rport-0:0-1':

  # cat /sys/class/fc_remote_ports/rport-N:N-N/fast_io_fail_tmo

  Install multipath-tools, and edit (or create) the /etc/multipath.conf
  file.  Add into the defaults section the setting for fast_io_fail_tmo;
  if it's already 5, replace 5 shown in the example with a different
  value than it's currently set to:

  defaults {
    fast_io_fail_tmo 5
  }

  If the multipath-tools-boot package is installed, rebuild the
  initramfs (with update-initramfs -u).

  Reboot for the parameter to take effect.

  After the system boots back up, multipath should have the drive(s)
  listed, e.g. in its 'multipath -ll' listing.

  Check the sysfs node that should have been modified (again replace
  rport-* with the correct numbers):

  # cat /sys/class/fc_remote_ports/rport-N:N-N/fast_io_fail_tmo

  It should show the value that was configured in multipath.conf.

  [Regression Potential]

  none.  This fixes multipath to correctly set sysfs attributes, as it
  did not work at all before.

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