[Bug 1780332] Re: vaultlocker does not ensure that udev is triggered to create /dev/disk/by-uuid/<uuid-in-luks-header> symlink and fails

[asi]

If you have properly installed device-mapper udev rules, cryptsetup is
internally synchronized to all symlinks and nodes creation (it should
never return only when udev is finished, that's why libdevmapper
internally uses semaphores and cookies per device).

Calling udev settle is just workaround for broken udev rules (or the
order of rules), you should never need that here...

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https://bugs.launchpad.net/bugs/1780332

Title:
  vaultlocker does not ensure that udev is triggered to create /dev/disk
  /by-uuid/<uuid-in-luks-header> symlink and fails

Status in vaultlocker:
  Fix Released
Status in cryptsetup package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  When an encrypted device is setup up a UUID (osd_fsid) is passed from
  the charm to be used in the cryptsetup command which accepts a UUID to
  place into the LUKS header (shown in cryptsetup luksDump <path-to-
  block-device>).

  https://github.com/openstack/charm-ceph-osd/blob/stable/18.05/lib/ceph/utils.py#L1788-L1804 
  UUID comes from osd_fsid

  https://github.com/openstack-charmers/vaultlocker/blob/8c9cb85dc3ed5dbf18c66a810d189a5230d85c34/vaultlocker/shell.py#L69-L80
  # else statement is used here
       block_uuid = str(uuid.uuid4()) if not args.uuid else args.uuid

       dmcrypt.luks_format(key, block_device, block_uuid) # creates a LUKS header
  # ...
       dmcrypt.luks_open(key, block_uuid) # sets up a device with device mapper decrypting it via dmcrypt

  https://github.com/openstack-
  charmers/vaultlocker/blob/d813233179bdf2eec8ed101c702a8e552a966f44/vaultlocker/dmcrypt.py#L44-L56

  This UUID is visible in blkid output

  /dev/sdc: UUID="<luks-header-uuid>" TYPE="crypto_LUKS"

  and a udev rule exists to create a /dev/disk/by-uuid/<luks-header-
  uuid> symlink (which is normally used for filesystem -> block device
  resolution)

  https://git.launchpad.net/~usd-import-team/ubuntu/+source/lvm2/tree/udev/13-dm-disk.rules.in#n25
  ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{ID_FS_UUID_ENC}=="?*", SYMLINK+="disk/by-uuid/$env{ID_FS_UUID_ENC}"

  
  Where vaultlocker fails is in luks_open command (right after luks_format) 

   # cryptsetup --batch-mode --key-file - open UUID=<luks-header-uuid>
  crypt-<luks-header-uuid> --type luks

  because it tries to access /dev/disk/by-uuid/<luks-header-uuid> which
  does not exist.

  This happens since udev rules are not re-triggered to create this
  symlink after a LUKS device is created.

  Solution: call the command below after luks_format before luks_open

  udevadm settle --exit-if-exists=/dev/disk/by-uuid/<luks-header-uuid-
  equal-to-osd-fsid>

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