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scsi_sync_pkt() is used to selectively synchronize a CPU's or device's view of the data associated with the SCSI packet that has been mapped
for I/O. This may involve operations such as flushes of CPU or I/O caches, as well as other more complex operations such as stalling until hardware
write buffers have drained.
This function need only be called under certain circumstances. When a SCSI packet is mapped for I/O using scsi_init_pkt(9F) and destroyed using scsi_destroy_pkt(9F), then an implicit scsi_sync_pkt() will be performed. However, if the memory object has been modified by either the device or a CPU
after the mapping by scsi_init_pkt(9F), then a call to scsi_sync_pkt()
is required.
If the same scsi_pkt is reused for a data transfer from memory to a device, then scsi_sync_pkt() must be called before calling scsi_transport(9F). If the same packet is reused for a data transfer from a device to memory scsi_sync_pkt() must be called
after the completion of the packet but before accessing the data in memory.
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