Comment 18 for bug 1565969

The systemd rule dates back to 2011 - so very old. But this had not manifested till we added further rules for multipath where we set flags for events which are coming from multipath device reload if multipath component underneath is down or it comes up (and hence multipath device needs to be reloaded). This is kind of event for which we really don't need to trigger all the existing rules again and trigger all scanning - it's just for the multipath dm device table reload which is transparent to any layer above or any mpath device user - so that's why we added DM_UDEV_DISABLE_OTHER_RULES_FLAG for such an event - to minimize the resource usage (in this case udev rule processing).

These new rules in multipath were added in RHEL7.0 then (which is also 2 years already!).

This problem has not manifested yet for other dm-based devices (like LVM) because these ones don't use the DM_UDEV_DISABLE_OTHER_RULES_FLAG after the device is set up and running - these require the scans and rules to be reevaluated if there's any reload compared to the multipath device where the content of the device is not changed during reloads when one of the paths is down or up.