File number field shows -1 whatever I do any operations, but the mt command and the tape driver works.

[CherryYang05]

• os version: centos7
• linux version: 3.10.0-1160
• arch: x86-64
• run command: lsscsi -g
• tape drive: 3580H9S LTO9
  [11:0:0:0] tape IBM ULT3580-HH9 N9B1 - /dev/sg0
• mt version: 1.7
• sas driver: mpt3sas
• tape driver: lin_tape-3.0.60-1.src.rpm, lin_taped-3.0.60-rhel7.x86_64.rpm
• ls /dev/ shows three tape devices: /dev/IBMtape(use mt command shows /dev/IBMtape: Resource temporarily unavailable), /dev/IBMtape0 and /dev/IBMtape0n. The last two device can work by using mt command.

Run command mt -f /dev/IBMtape0n status, it shows like below:

SCSI 2 tape drive:
File number=-1, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x60 (no translation).
Soft error count since last status=0
General status bits on (41000000):
 BOT ONLINE

The File number equals -1. Does it work correctly?

Then I setup the blocksize: mt -f /dev/IBMtape0n setblk 512

Run as above, it shows:

SCSI 2 tape drive:
File number=-1, block number=0, partition=0.
Tape block size 512 bytes. Density code 0x60 (no translation).
Soft error count since last status=0
General status bits on (41000000):
 BOT ONLINE

And then I try to write a 1KB file(filename is "1k") to the tape, using command tar cbvf 1 /dev/IBMtape0n 1k, and check its block number mt -f /dev/IBMtape0n tell, shows At block 6, that's right.

Now check the status:

SCSI 2 tape drive:
File number=-1, block number=6, partition=0.
Tape block size 512 bytes. Density code 0x60 (no translation).
Soft error count since last status=0
General status bits on (1000000):
 ONLINE

Why the File number field is also -1? And how to correct it?