sdev
sdev is about to be destroyed for hot/warm unplugging. If this unplugging was initiated by libata as indicated by NULL dev->sdev, this function doesn't have to do anything. Otherwise, SCSI layer initiated warm-unplug is in progress. Clear dev->sdev, schedule the device for ATA detach and invoke EH.
Defined by SCSI layer. We don't really care.
Jeff Garzik