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From: joemu@nscpdc.NSC.COM (Joe Mueller)
Newsgroups: comp.sys.nsc.32k
Subject: Re: ICM3216: appending on tapes.
Message-ID: <888@nscpdc.NSC.COM>
Date: Wed, 22-Jul-87 13:29:02 EDT
Article-I.D.: nscpdc.888
Posted: Wed Jul 22 13:29:02 1987
Date-Received: Sat, 25-Jul-87 01:58:25 EDT
References: <1857@imag.UUCP> <219@augean.OZ>
Organization: National Semiconductor, Portland Development Center, Portland, OR
Lines: 30
Summary: appending to tape problem revisited

In a previous article Grahm Menhennitt writes:
> If your tape device driver is written correctly you won't have this problem.
> The correct way of handling a close on a tape device that has been open for
> writing is to mark it with an EOM. As Joe says this is simply two EOF marks.
> The trick is that after writing the second mark the device driver should
> backspace the tape to the point between the two marks. Then, if the non-rewind
> tape device was used and the device is subsequently re-opened for writing,
> the second EOF will be overwritten and the tape will correctly have one EOF
> between the two files.

Interesting idea, but impossible to do on emulex controllers. You can only
space forward.

In article <219@augean.OZ>, idall@augean.OZ (Ian Dall) writes:
> What is really needed is a modification to the "mt" command to support
> "mt eod". This can be done using the SCSI "Pivot" driver but use care -
> stuff it up and you will crash the system (or worse). The more correct
> solution is to add an extra ioctl code to the tc driver.

It's funny (but I'm happy) that someone proposed the exact solution I came
up with. I've added a new option to the mt command called "append". It uses a
new ioctl that positions the tape to the end of recorded data. You may only
write information at the very end of all recorded information or starting at
the beginning of the tape. It is still impossible (for example) to write 3
files to the tape, rewind, forward over 2 of the files, and overwrite the
third.

I'm always happy to consider improvements to our device drivers, if you
have any other suggestions, try sending them directly to me or go through
our techincal support group.