Reservation conflict logging

When the device driver receives a reservation conflict on a tape drive command, it logs the conflict to the kernel debug buffer (which is typically echoed to /var/log/messages). Before the error is logged, the device driver determines whether a SCSI Persistent Reservation is active on the target tape drive. If it is, it gets the reserving host initiator WWPN (worldwide port name). If successful, the device driver posts the message

lin_tape: reserve held by xxxxxxxx

to the debug buffer. To prevent multiple identical entries in the error log, subsequent reservation conflicts from the same reserving host WWPN are not logged.