[Bug 1874501] Re: vgscan --mknodes creates block device multipath nodes in /dev/mapper

[Ryan Harper]

This patch configures the dm_task to use the
DM_UDEV_DISABLE_LIBRARY_FALLBACK udev flag to prevent calls to
dm_mknodes() from using the library fallback code.

Another possible fix would be to obtain a different return code from
vgscan.c where it does not detect any VGs  and then calls the mknode
path due to the argument passed to the cli


    maxret = process_each_vg(cmd, argc, argv, NULL, NULL, 0, 0, NULL, &_vgscan_single);

    /* at this point, this could return some indication if vgs were found
       such that we could skip the vgmknodes() if no vgs were found */
                                                                               
    if (arg_is_set(cmd, mknodes_ARG)) {                                        
        ret = vgmknodes(cmd, argc, argv);                                      
        if (ret > maxret)                                                      
            maxret = ret;                                                      
    }                        


** Patch added: "disable-library-fallback-in-vgscan-mknodes.patch"
   https://bugs.launchpad.net/ubuntu/+source/lvm2/+bug/1874501/+attachment/5362656/+files/disable-library-fallback-in-vgscan-mknodes.patch

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https://bugs.launchpad.net/bugs/1874501

Title:
  vgscan --mknodes creates block device multipath nodes in /dev/mapper

Status in Ubuntu on IBM z Systems:
  New
Status in lvm2 package in Ubuntu:
  Confirmed

Bug description:
  Description:    Ubuntu 20.04 LTS
  Release:        20.04

  # apt-cache policy multipath-tools
  multipath-tools:
    Installed: 0.8.3-1ubuntu2
    Candidate: 0.8.3-1ubuntu2
    Version table:
   *** 0.8.3-1ubuntu2 500
          500 http://ports.ubuntu.com/ubuntu-ports focal/main s390x Packages
          100 /var/lib/dpkg/status

  
  /dev/mapper/mpatha is symlink which points to ../../dm-X device

  /dev/mapper/mpath is block device

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: multipath-tools 0.8.3-1ubuntu2
  ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
  Uname: Linux 5.4.0-26-generic s390x
  NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: s390x
  CasperMD5CheckResult: pass
  CasperVersion: 1.445
  Date: Thu Apr 23 17:32:12 2020
  LiveMediaBuild: Ubuntu-Server 20.04 LTS "Focal Fossa" - Release s390x (20200423.1)
  ProcEnviron:
   TERM=screen.xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=C.UTF-8
   SHELL=/bin/bash
  SourcePackage: multipath-tools
  UpgradeStatus: No upgrade log present (probably fresh install)
  modified.conffile..etc.multipath.conf:
   defaults {
       user_friendly_names yes
       skip_kpartx no
       verbosity 4
   }
  mtime.conffile..etc.multipath.conf: 2020-04-23T15:47:28.659850

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