ubifs volumes have a UUID and the built-in blkid is able to determine
it. The disk/by-uuid symlink isn't created because ubifs volumes are
not on block devices but on SUBSYSTEM="ubi" devices. See #20071.
Allow ubi subsystem devices to be processed by the persistent storage
rules too. The kernel device name matching already allows ubi* to pass.
The existing rules are sufficient to create the link.
The links look like other by-uuid symlinks, for example:
/dev/disk/by-uuid/
9a136158-585b-4ba4-9b70-
cbaf2cf78a1c -> ../../ubi0_1
ACTION=="remove", GOTO="persistent_storage_end"
ENV{UDEV_DISABLE_PERSISTENT_STORAGE_RULES_FLAG}=="1", GOTO="persistent_storage_end"
-SUBSYSTEM!="block", GOTO="persistent_storage_end"
+SUBSYSTEM!="block|ubi", GOTO="persistent_storage_end"
KERNEL!="loop*|mmcblk*[0-9]|msblk*[0-9]|mspblk*[0-9]|nvme*|sd*|sr*|vd*|xvd*|bcache*|cciss*|dasd*|ubd*|ubi*|scm*|pmem*|nbd*|zd*", GOTO="persistent_storage_end"
# ignore partitions that span the entire disk