st: Fix MTMKPART to work with newer drives

Change the MTMKPART operation of the MTIOCTOP ioctl so that it works
also with current drives (LTO-5/6, etc.). Send a separate FORMAT MEDIUM
command if the partition mode page indicates that this is required. Use
LOAD to position the tape at the beginning of tape.

The operation is extended so that if the argument is negative, its
absolute value specifies the size of partition 0, which is the
physically first partition of the tape.

Signed-off-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Tested-by: Shane M Seymour <shane.seymour@hpe.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/scsi/st.txt

@@ -2,7 +2,7 @@ This file contains brief information about the SCSI tape driver.
 The driver is currently maintained by Kai Mäkisara (email
 Kai.Makisara@kolumbus.fi)
 
-Last modified: Sun Aug 29 18:25:47 2010 by kai.makisara
+Last modified: Tue Feb  9 21:54:16 2016 by kai.makisara
 
 
 BASICS
@@ -408,10 +408,15 @@ MTSETPART Moves the tape to the partition given by the argument at the
 	specified by MTSEEK. MTSETPART is inactive unless
 	MT_ST_CAN_PARTITIONS set.
 MTMKPART Formats the tape with one partition (argument zero) or two
-	partitions (the argument gives in megabytes the size of
-	partition 1 that is physically the first partition of the
-	tape). The drive has to support partitions with size specified
-	by the initiator. Inactive unless MT_ST_CAN_PARTITIONS set.
+	partitions (argument non-zero). If the argument is positive,
+	it specifies the size of partition 1 in megabytes. For DDS
+	drives and several early drives this is the physically first
+	partition of the tape. If the argument is negative, its absolute
+	value specifies the size of partition 0 in megabytes. This is
+	the physically first partition of many later drives, like the
+	LTO drives from LTO-5 upwards. The drive has to support partitions
+	with size specified by the initiator. Inactive unless
+	MT_ST_CAN_PARTITIONS set.
 MTSETDRVBUFFER
 	Is used for several purposes. The command is obtained from count
         with mask MT_SET_OPTIONS, the low order bits are used as argument.