zvol_wait — wait for ZFS volume links to appear in /dev

       When  a ZFS pool is imported, the volumes within it will appear as block devices.  As they're registered,
       udev(7) asynchronously creates symlinks under /dev/zvol using the volumes' names.   zvol_wait  will  wait
       for all those symlinks to be created before exiting.

       zvol_wait — wait for ZFS volume links to appear in /dev

udev(7)

OpenZFS                                           May 27, 2021                                      ZVOL_WAIT(1)

zvol_wait