Comment 20 for bug 1780332

asi,

Thanks for the guidance.

Attached some outputs.

> Look for "dmsetup udevcomplete" call in udev rules.

ubuntu@maas-vhost6:/lib/udev/rules.d$ grep -RiP udevcomplete
55-dm.rules:ENV{DM_COOKIE}=="?*", RUN+="/sbin/dmsetup udevcomplete $env{DM_COOKIE}"

> Sometimes it is hidden by the fact that libdevampper could fallback to device internal nodes creation because it verifies that udev nodes were created (the old way used when you compile it without udev support).

At least I can see that it is not disabled explicitly for xenial in the build scripts:

https://git.launchpad.net/~usd-import-team/ubuntu/+source/cryptsetup/tree/configure?h=ubuntu/xenial-updates#n15870

# Check whether --enable-udev was given.
if test "${enable_udev+set}" = set; then :
  enableval=$enable_udev;
else
  enable_udev=yes
fi

https://git.launchpad.net/~usd-import-team/ubuntu/+source/cryptsetup/tree/debian/rules?h=ubuntu/xenial-updates#n43

> This must be the last call in udev chain rules related to device-mapper devices. (Run cryptsetup with --debug and you will see that sync point.)

Do you remember anything specific? I do not see anything above this

# Key length 32, device size 16777216 sectors, header size 2050 sectors.
# Releasing crypt device /dev/sdb context.
# Releasing device-mapper backend.
# Unlocking memory.
Command successful.
14:09:07.630619660

in the attached output that would definitively resemble a sync point ("Releasing context..." could be it but I am not sure without looking at the code).

journalctl -u systemd-udevd.service -f -o short-precise

# ...
Sep 15 14:09:07.634172 maas-vhost6 systemd-udevd[3793]: IMPORT builtin 'blkid' /lib/udev/rules.d/60-persistent-storage.rules:76
Sep 15 14:09:07.634285 maas-vhost6 systemd-udevd[3793]: probe /dev/sdb raid offset=0
Sep 15 14:09:07.634399 maas-vhost6 systemd-udevd[3793]: LINK 'disk/by-uuid/fcdd1397-8fb7-410c-b343-a7bb1a2f83d0' /lib/udev/rules.d/60-persistent-storage.rules:79

# ...

Sep 15 14:09:07.635434 maas-vhost6 systemd-udevd[3793]: found 'b8:16' claiming '/run/udev/links/\x2fdisk\x2fby-uuid\x2ffcdd1397-8fb7-410c-b343-a7bb1a2f83d0'
Sep 15 14:09:07.635547 maas-vhost6 systemd-udevd[3793]: creating link '/dev/disk/by-uuid/fcdd1397-8fb7-410c-b343-a7bb1a2f83d0' to '/dev/sdb'
Sep 15 14:09:07.635659 maas-vhost6 systemd-udevd[3793]: preserve already existing symlink '/dev/disk/by-uuid/fcdd1397-8fb7-410c-b343-a7bb1a2f83d0' to '../../sdb'