[Bug 1486370] Re: ISST-LTE: not all mpath device files are symbol link

[Ming-Xun Zhong]

Hi,

I encounter this bug on Precise, and apply these two patch from upstream
fix it.

http://git.opensvc.com/gitweb.cgi?p=multipath-tools/.git;a=commit;h=1b8082c8fc81374ba7b0204f6de8f71de5500192
http://git.opensvc.com/gitweb.cgi?p=multipath-tools/.git;a=commit;h=9a632fff65df3bf82a3ef70f62319a1c45f3c028

In my environment it easily reproduce with

Case 1:
while true; do kpartx -d -p -part /dev/dm-2;udevadm settle;  kpartx   -a -p -part /dev/dm-2;  udevadm settle;done

Case 2:
while true; do multipath -F;  multipath; done

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Title:
  ISST-LTE: not all mpath device files are symbol link

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

Bug description:
  [Impact]
  Minimal impact, this is limited to aesthetic issues; devices should if possible all be actual block device nodes rather than symlinks.

  [Test case]
  1) ls -l /dev/mapper
  2) Reboot, try again.

  [Regression potential]
  Timing issues may cause delays in generating device nodes or symlinks due to the need for multipath-tools, device-mapper and udev to synchronize.

  ---

  == Comment: #0 - Ping Tian Han <pthan at cn.ibm.com> - 2015-07-21 23:38:48 ==
  ---Problem Description---
  Some mpath devices in /dev/mapper are symbol links to /dev/dm-<n>, but there are exceptions:

  % ls -l /dev/mapper
  total 0
  crw------- 1 root root  10, 236 Jul 21 20:46 control
  lrwxrwxrwx 1 root root        7 Jul 21 20:46 mpath0 -> ../dm-0
  brw------- 1 root root 252,   4 Jul 21 20:46 mpath0-part1
  brw------- 1 root root 252,   6 Jul 21 20:46 mpath0-part2
  brw------- 1 root root 252,   7 Jul 21 20:46 mpath0-part3
  lrwxrwxrwx 1 root root        7 Jul 21 20:46 mpath1 -> ../dm-1
  brw-rw---- 1 root disk 252,   2 Jul 21 20:46 mpath2
  lrwxrwxrwx 1 root root        7 Jul 21 20:46 mpath3 -> ../dm-3
  lrwxrwxrwx 1 root root        7 Jul 21 20:46 mpath4 -> ../dm-5

  mpath2 isn't a symbol link.

  % sudo dmestup info mpath2
  sudo: dmestup: command not found
  % sudo dmsetup info mpath2
  Name:              mpath2
  State:             ACTIVE
  Read Ahead:        256
  Tables present:    LIVE
  Open count:        0
  Event number:      4
  Major, minor:      252, 2
  Number of targets: 1
  UUID: mpath-36005076304ffc69f0000000000000469

  % sudo dmsetup info /dev/dm-2
  Name:              mpath2
  State:             ACTIVE
  Read Ahead:        256
  Tables present:    LIVE
  Open count:        0
  Event number:      4
  Major, minor:      252, 2
  Number of targets: 1
  UUID: mpath-36005076304ffc69f0000000000000469

  Contact Information = Ping Tian Han/pthan at cn.ibm.com,   Chanh H
  Nguyen/chnguyen at us.ibm.com

  ---uname output---
  Linux onyxlp2 3.19.0-22-generic #22~14.04.1-Ubuntu SMP Wed Jun 17 10:03:39 UTC 2015 ppc64le ppc64le ppc64le GNU/Linux

  Machine Type = na

  ---Steps to Reproduce---
   1. install ubuntu on onyxlp2, which has mpath device
  2. ls /dev/mapper, see some mpath device file isn't symbol link

  Userspace tool common name: na

  The userspace tool has the following bit modes: 64-bit

  Userspace rpm: na

  Userspace tool obtained from project website:  na

  == Comment: #6 - Mauricio Faria De Oliveira <mauricfo at br.ibm.com> - 2015-08-18 12:33:17 ==
  This shouldn't be a problem at all.
  Either symlinks to the dm devices or block devices which refer to them directly (via major:minor number) will work.

  It isn't ideal, though.

  == Comment: #7 - Mauricio Faria De Oliveira <mauricfo at br.ibm.com> - 2015-08-18 12:35:34 ==
  BTW, that expectation is per the SRU policy.

  And the problem cause is likely a race involving udev rules (multipath
  & kpartx), and possibly multipathd.

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