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8.1.1.2: Tape motion commands

When using the mt program to send tape motion commands, i.e. commands which alter the position of the tape R/W head relative to the tape, it doesn't make any sense to use the auto-rewinding devices. The reason is simple: `auto-rewinding' means that the tape is rewound when the tape device is closed. However, the tape device is kept open at most for the life time of the program which has opened it. This means

mt -f /dev/qft0 asf 1

will happily move the tape head to the first file mark, position on the EOT side of that file mark (see MTFSF, see File marks) and then the mt program is finished. Which means that it closes the tape device and as a result the tape is rewound because `/dev/qft0' is an auto-rewinding device (note the missing N in front of the `qft0').

So you end up with a tape that is located at BOT, and not at the EOT side of the first file mark. So, the following would be the correct command. Note the N in front of the device name.

mt -f /dev/nqft0 asf 1

Tape motion commands are available through the following MTIOCTOP (see MTIOCTOP) ioctls. Only ioctls are listed that would move the tape head away from BOT(1)

MTFSF
MTBSF
MTFSR
MTBSR
MTBSFM
MTFSFM
MTEOM
MTSEEK


(1) Obviously, when sending a tape command that causes a rewind operation itself it doesn't matter whether one uses the auto-rewinding or non-rewinding devices as in this case one ends up with the tape positioned at BOT anyway.


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