Comment 2 for bug 1967190

Reviewed: https://review.opendev.org/c/starlingx/kernel/+/835916
Committed: https://opendev.org/starlingx/kernel/commit/6fe8d6083263e0fdbce0b6ba9e59ed10ebd932e6
Submitter: "Zuul (22348)"
Branch: master

commit 6fe8d6083263e0fdbce0b6ba9e59ed10ebd932e6
Author: M. Vefa Bicakci <email address hidden>
Date: Wed Mar 30 13:39:01 2022 -0400

    kernel: Disable NVMe multi-path kconfig option

    This commit disables the NVMe multi-path kernel configuration option,
    which was introduced with kernel v4.15-rc1, and is included in
    StarlingX's v5.10-based kernel.

    This feature exposes block devices such as "nvme0c0n1" in
    /sys/class/block with the "hidden" attribute set to 1; however, the
    older anaconda installer and user-space packages that StarlingX inherits
    from CentOS 7 were not programmed to ignore such hidden block devices.
    This results in anaconda reporting an error when probing the disks on
    the system and aborting the installation. Similarly, the "lsblk" program
    reports warnings about unrecognized block devices.

    Both of these issues were fixed upstream with the following commits:
    - https://github.com/storaged-project/blivet/commit/8957eb1f82a37542ea1ae3990b6068b3cf90a3be
    - https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=c8487d854ba5cf5bfcae78d8e5af5587e7622351

    Given the difficulty of auditing all of CentOS 7's user-space for
    potential incompatibilities with NVMe multi-path support, this commit
    disables this feature.

    The following options were considered to disable this option:
    - Unset CONFIG_NVME_MULTIPATH (implemented in this commit)
    - Use the kernel command line argument nvme_core.multipath=0
    - Use a modprobe.d configuration file with the following contents:
      "options nvme_core multipath=0".

    Of these options, the first was chosen to ensure non-error-prone
    consistency across all StarlingX configurations, even though the latter
    two options are more flexible.

    Verification
    - The issue was confirmed to exist on a standalone server with NVMe
      multi-path support, by attempting to install StarlingX using an ISO
      image built from StarlingX's master branch, in All-in-One simplex
      mode.
    - An ISO image was successfully built with this commit using a
      monolithic incremental build procedure.
    - The built ISO image was used to install StarlingX succcessfully onto
      the same standalone server in All-in-One simplex mode.
    - Basic disk operations were carried out by creating a partition and a
      file system on the NVMe drive, as well as using dd in a loop to write
      zero bytes to a file created in the same file system.

      (Note that the same test procedure was not repeated with a server that
      has unaffected NVMe controllers due to lab availability constraints.
      Inspection of the kernel's NVMe multi-path support code indicates that
      the kernel falls back to non-multi-path code paths when an NVMe
      controller does not support this feature.)

    Closes-Bug: 1967190
    Change-Id: I791cfb6d7bc141e2114dea5e7f8d648b6df81f14
    Signed-off-by: M. Vefa Bicakci <email address hidden>