pythonlinuxioctlfcntlmt

Write magnetic tape end of record linux

Task is create two record with different sizes within one file entry. I'm using python 3.4.5 for testing:

import fcntl
import os
import struct

MTIOCTOP = 0x40086d01  # refer to mtio.h
MTSETBLK = 20

fh = os.open('/dev/st2', os.O_WRONLY )
fcntl.ioctl(fh, MTIOCTOP, struct.pack('hi', MTSETBLK, 1024))
os.write(fh, b'a'*1024)
fcntl.ioctl(fh, MTIOCTOP, struct.pack('hi', MTSETBLK, 2048))
os.write(fh, b'b'*2048)
os.close(fh)


[root@dev2 mhvtl]# tcopy /dev/st2
file 0: block size 4096: 1 records
file 0: eof after 1 records: 4096 bytes <<< should be 2 records
eot
total length: 4096 bytes
[root@dev2 mhvtl]# ^C

Is there an ioctl opt code that will initiate a new record on the tape with variable record length. Or any other way to work around this bug?

Solution

  • Issue was with tcopy, it uses block size on device instead of detecting it.

    fcntl.ioctl(fh, MTIOCTOP, struct.pack('hi', MTSETBLK, 0))

    after last write allowed tcopy to display data as intended.