/lib/udev/rules.d/60-zvol.rules is in zfsutils-linux 0.7.5-1ubuntu15.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | # Persistent links for zvol
#
# persistent disk links: /dev/zvol/dataset_name
# also creates compatibility symlink of /dev/dataset_name
KERNEL=="zd*" SUBSYSTEM=="block" ACTION=="add|change" PROGRAM="/lib/udev/zvol_id $tempnode" SYMLINK+="zvol/%c %c"
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