[Bug 1838525] Re: LVM setup fails to install grub on virtio storage

Mon Oct 7 18:55:07 UTC 2019

The following commit:

commit 417e52c13a8156b11c25c411d44bda8b32bf87e4
Author: Peter Rajnoha <prajnoha at redhat.com>
Date:   Tue Feb 18 07:27:21 2014

    udev: create /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> symlink for a PV
    
    We already have /dev/disk/by-id/dm-uuid-... (which encompasses the
    VG UUID and LV UUID in case of LVs since the mapping's UUID is
    VG+LV UUID together) and /dev/disk/by-id/dm-name-... (which encompasses
    the VG and LV name in case of LVs).
    
    This patch addds /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> that completes
    this scheme and makes navigation a bit easier using PV UUIDs since
    one can navigate using PV UUIDs only and there's no need to do extra
    PV UUID <--> kernel name matching (the PV UUID is stable across reboots).
    This may come in handy in various scripts.
    
    Since we already have the PV UUID stored in udev database (as a result
    of blkid call - returned in ID_FS_UUID blkid's variable), this operation
    is very cheap indeed, just creating the extra one symlink.

diff --git a/WHATS_NEW b/WHATS_NEW
index 39e8b886a..5bb37d8ad 100644
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.106 - 
 ====================================
+  Create /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> symlink for each PV via udev.
   lvcreate computes RAID4/5/6 stripes if not given from # of allocatable PVs.
   Fix merging of old snapshot into thin volume origin.
   Use --ignoreskippedcluster in lvm2-monitor initscript/systemd unit.
diff --git a/udev/69-dm-lvm-metad.rules.in b/udev/69-dm-lvm-metad.rules.in
index e8304b5e0..bd75fc8ef 100644
--- a/udev/69-dm-lvm-metad.rules.in
+++ b/udev/69-dm-lvm-metad.rules.in
@@ -34,6 +34,9 @@ ENV{DM_MULTIPATH_DEVICE_PATH}=="1", GOTO="lvm_end"
 # Inform lvmetad about any PV that is gone.
 ACTION=="remove", GOTO="lvm_scan"
 
+# Create /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> symlink for each PV
+ENV{ID_FS_UUID_ENC}=="?*", SYMLINK+="disk/by-id/lvm-pv-uuid-$env{ID_FS_UUID_ENC}"
+
 # If the PV is a special device listed below, scan only if the device is
 # properly activated. These devices are not usable after an ADD event,
 # but they require an extra setup and they are ready after a CHANGE event.

was the one responsible to add the change that causes:

/dev/disk/by-id/ to be populated with the LVM volume (not the entire
disk), breaking the current installer logic. There are 2 alternatives
here:

        To revert this change for current release, since this rule was
added to "make navigation a bit easier using PV UUIDs", as the commit
says. We would worry about installer changes in the next release.

	Another possibility would be to change the logic inside "grub-mkdevicemap.c: make_device_map()->grub_util_iterate_devices()" to ignore all symlinks from /dev/disk/by-id/ containing lvm-pv-uuid-*. We would not have to worry about this in the next release if using debian-installer. I'm choosing this option because ubuntu foundations already faced a similar situation, when grub-mkdevicemap.c file was removed from grub2 code and they re-added it by using a quilt patch, assuming it was the easiest and better to maintain. I'm doing something similar, patching the patch that creates grub-mkdevicemap.c file again.
	
	Another option would be to change grub-installer package/logic. Unfortunately, a few days before the full freeze, I don't think messing with the instaler would be a good option to avoid regressions (potential regression item would grow in significance).

So I'm going with (2) and providing a MR for Eoan to be reviewed in a
few moments.

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https://bugs.launchpad.net/bugs/1838525

Title:
  LVM setup fails to install grub on virtio storage

Status in debian-installer package in Ubuntu:
  In Progress
Status in grub2 package in Ubuntu:
  In Progress
Status in lvm2 package in Ubuntu:
  In Progress
Status in debian-installer package in Debian:
  New

Bug description:
  Comment #26 has the TL;DR version of the problem.
  https://bugs.launchpad.net/ubuntu/+source/debian-installer/+bug/1838525/comments/26

  [Original Description]

  The Eoan debian-installer ISO fails to install GRUB on LVM installs
  with virtio storage, as it runs grub-install with /dev/mapper as a
  target (a directory), even if instructed to target a device.

  The following steps to reproduce have been prepared running the
  20190730 build, but this has been broken since about June 18, 2019.
  Steps to reproduce:

  $ md5sum eoan-server-amd64.iso
  f591e30485e5f0b5117f6c116e538c42  eoan-server-amd64.iso
  $ qemu-img create -f raw disk1.img 8G
  Formatting 'disk1.img', fmt=raw size=8589934592
  $ kvm -m 1024 -boot d -cdrom eoan-server-amd64.iso -drive file=disk1.img,if=virtio

  Proceed with all the defaults. In the "Partition disk" step select
  "Guided - use entire disk and set up LVM". Go ahead accepting the
  defaults. At the "Install the GRUB boot loader" step select "/dev/vda"
  as the target device. The installer will actually run `grub-install
  --force /dev/mapper` and fail after a while. The wrong command is
  visible both in the d-i screen and by running `ps` on a different
  console.

  Full installer syslog: http://paste.ubuntu.com/p/qtZy86dTp6/

  It's interesting how this doesn't happen when not using virtio. If
  from the commands above the "if=virtio" option is dropped then
  everything works as expected. In this case the target block device is
  called /dev/sda instead of /dev/vda.

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