+
+------------
+ SEQUENCING
+------------
+
+Kernel does not serialize hotplug events. It increments SEQNUM environmental
+variable for each successive hotplug invocation. Normally, mdev doesn't care.
+This may reorder hotplug and hot-unplug events, with typical symptoms of
+device nodes sometimes not created as expected.
+
+However, if /dev/mdev.seq file is found, mdev will compare its
+contents with SEQNUM. It will retry up to two seconds, waiting for them
+to match. If they match exactly (not even trailing '\n' is allowed),
+or if two seconds pass, mdev runs as usual, then it rewrites /dev/mdev.seq
+with SEQNUM+1.
+
+IOW: this will serialize concurrent mdev invocations.
+
+If you want to activate this feature, execute "echo >/dev/mdev.seq" prior to
+setting mdev to be the hotplug handler. This writes single '\n' to the file.
+NB: mdev recognizes /dev/mdev.seq consisting of single '\n' character
+as a special case. IOW: this will not make your first hotplug event
+to stall for two seconds.