[Bug 1996958] Re: [Azure] 18.04 - non-unique PATH_ID for SCSI disks

[Mauricio Faria de Oliveira]

I have verified the scenario that Seyeong mentioned
where the patch apparently dit not make a difference
(SCSI disks with LUN numbers greater than 1, eg, 5).

My observation is it indeed works/makes a difference.

He went out on vacation (so I'm reassigning the bug), and
cannot confirm this, but per internal comments I believe
that observation was based on /dev/disk/by-path symlinks,
which are not updated automatically (on test pkg install).

The PATH_IDs obtained with `udevadm info` were correct,
though, so it's working as expected (just needed reboot).

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Title:
  [Azure] 18.04 - non-unique PATH_ID for SCSI disks

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  In Progress

Bug description:
  [Impact]

   * The PATH_ID for SCSI disks on Azure/Hyper-V might not be unique
     with the systemd/udev version in Ubuntu 18.04 LTS (Bionic Beaver).

   * This cause issues on applications that require unique PATH_IDs;
     for example Veritas Dynamic Multi-Pathing (DMP).

   * The fix introduces changes to PATH_ID format/values for VMBUS,
     which would break stable names/links, so it must be an opt-in.

   * The kernel command line option 'udev.new_vmbus_path_id' (boolean)
     can be used to opt in to (different) unique PATH_IDs.

   * It's not used by default (i.e., no behavior change by default).

  [Test Plan]

   1. Launch an Ubuntu 18.04 VM on Azure
   2. Add extra disks to the VM
   3. Check the disks PATH_ID for (non-)unique values
   4. (Opt-in for the fix with kernel cmdline option; repeat 3.)

   * Before:

    $ lsscsi | grep /dev/sd
    [0:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sdc
    [0:0:0:1]    disk    Msft     Virtual Disk     1.0   /dev/sdd
    [1:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sda
    [1:0:0:1]    disk    Msft     Virtual Disk     1.0   /dev/sdb

    $ for sd in /dev/sd?; do \
      udevadm test-builtin path_id /block/${sd#/dev} \
        2>/dev/null | grep ID_PATH=; \
      done | sort | uniq -c
    2 ID_PATH=acpi-VMBUS:00-scsi-0:0:0:0
    2 ID_PATH=acpi-VMBUS:00-scsi-0:0:0:1

   * After:

    Opt-in mechanism:

    $ cat <<EOF | sudo tee /etc/default/grub.d/99-new-vmbus-path-id.cfg
    GRUB_CMDLINE_LINUX="\$GRUB_CMDLINE_LINUX udev.new_vmbus_path_id"
    EOF

    $ sudo update-grub
    $ sudo reboot

    $ for sd in /dev/sd?; do \
      udevadm test-builtin path_id /block/${sd#/dev} \
        2>/dev/null | grep ID_PATH=; \
      done | sort | uniq -c
    1 ID_PATH=acpi-VMBUS:00-vmbus-f8b3781a1e824818a1c363d806ec15bb-lun-0
    1 ID_PATH=acpi-VMBUS:00-vmbus-f8b3781a1e824818a1c363d806ec15bb-lun-1
    1 ID_PATH=acpi-VMBUS:00-vmbus-f8b3781b1e824818a1c363d806ec15bb-lun-0
    1 ID_PATH=acpi-VMBUS:00-vmbus-f8b3781b1e824818a1c363d806ec15bb-lun-1

  [Where problems might occur]

   * The PATH_ID property of SCSI disks on Azure/Hyper-V
     (ie, on VMBUS) might display problems, and impact
     applications/userspace that use /dev/disk/by-path.

   * There are no functional changes in the existing code path
     (see patch for '37' and related math).  The new code path
     is guarded with an opt-in option (not used by default).

  [Other Info]

   * upstream patch:
     https://github.com/systemd/systemd/commit/cf3fabacaa141a1224a2ad239806a1fa28b51687

   * present in Focal and later:

  systemd.git$ git describe --contains cf3fabacaa141a1224a2ad239806a1fa28b51687
  v239~511

  $ rmadison -a source systemd
   systemd | 204-5ubuntu20     | trusty          | source
   systemd | 204-5ubuntu20.31  | trusty-security | source
   systemd | 204-5ubuntu20.31  | trusty-updates  | source
   systemd | 229-4ubuntu4      | xenial          | source
   systemd | 229-4ubuntu21.27  | xenial-security | source
   systemd | 229-4ubuntu21.31  | xenial-updates  | source
   systemd | 237-3ubuntu10     | bionic          | source
   systemd | 237-3ubuntu10.56  | bionic-security | source
   systemd | 237-3ubuntu10.56  | bionic-updates  | source
   systemd | 245.4-4ubuntu3    | focal           | source
   systemd | 245.4-4ubuntu3.15 | focal-security  | source
   systemd | 245.4-4ubuntu3.18 | focal-updates   | source
   systemd | 245.4-4ubuntu3.19 | focal-proposed  | source
   systemd | 249.11-0ubuntu3   | jammy           | source
   systemd | 249.11-0ubuntu3.6 | jammy-updates   | source
   systemd | 251.4-1ubuntu7    | kinetic         | source
   systemd | 251.4-1ubuntu7    | lunar           | source

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