Partition: Mask DM/LVM rules, don't stop udev

[jrha]

While partitions are being created and wiped, mask udev rules related to Device Mapper and LVM to prevent partitions from being activated automatically. This replaces the previous solution of completely stopping udev during these operations, which prevented the use of device names created by the persistent storage rules.

Fixes #105.

[jrha]

This solution works fine for us at RAL, but it's not been exhaustively tested.

[jrha]

In theory systemd-udev uses inotify to watch /usr/lib/udev/rules.d/ and /etc/udev/rules.d, but we could also throw a udevadm control --reload-rules && udevadm trigger in there to be sure.

[iddecker]

We are having the same issue at UGent when trying to use the /dev/disk/by-path names for disk devices.

With your change, the install hangs when trying to run lvm. Adding udevadm control --reload-rules && udevadm trigger when masking and unmasking the rules seems to fix that.

I don't really know what would be different in our setup that causes this issue to show up here.

Something to note: in Partition.pm, the code that is generated checks for the partition in /proc/partitions. The /dev/disk/... paths will never be in there, so the grep will never match anything. This will need something like

--- /usr/lib/perl/NCM/./Partition.pm    2021-05-10 11:41:46.000000000 +0200
+++ ./Partition.pm      2024-10-31 18:00:47.366800468 +0100
@@ -618,11 +618,14 @@
     # This will make the partitioning phase much faster.
     # Partitions are also wiped before they are removed.
     print <<EOF;
-if grep -q $self->{devname} /proc/partitions
+DISKDEV=`readlink -f /dev/$self->{devname}`
+if [[ "\$DISKDEV" =~ "/dev/" ]] ; then
+if grep -q \${DISKDEV#/dev/} /proc/partitions
 then
     wipe_metadata $path
     parted $devpath -s rm $n
 fi
+fi
 EOF
 }

to actually check for the correct partition. A different approach might be to check if the path exists in /dev.