From: utzoo!decvax!duke!unc!smb
Newsgroups: net.unix-wizards
Title: Re: mag tape ballots counted
Article-I.D.: unc.3730
Posted: Sun Jul 25 21:33:58 1982
Received: Wed Jul 28 06:09:49 1982


Dare I suggest that UNIX follow the OS/360 model?  Well, let me cite
Multics instead -- it's a bit nicer, and there UNIX's debt is clear.

Most of the time, I want to treat a file on a tape as a *file*.  I rarely
care about where on the tape it's located -- I want to find it, and read
it, as many times as necessary to do what needs to be done.  For example,
I rarely extract a tar image without looking at the contents first; I *never*
do if I'm running as root (and when will someone write some mods to tar
that will let it rename files...?).  When you mount a tape in OS/360 or
Multics, you specify a file number.  The operating system finds the file;
when you close the tape drive, it repositions the tape to the start of
that same file.  You can read it over and over again if you'd like.
(Both Multics and OS allow "labelled tapes"; Multics permits you to
specify the file-name on the tape instead of the sequence number, while OS
requires that they match.)  There should be ioctl() calls to change the
standard file number; calls like "write tape mark" should automatically
increment it.  Tape motion calls should of course exist -- but they should
co-exist with this basic principle.  Thus, 'backspace record' should halt
at the tape mark -- you can't seek past the beginning of a file.  But
'rewind' should reset the file number to 1.  (Amdahl's UTS system has
some of this implemented, though not the file-number concept.  One nice
thing they do do is generate a signal when a write encounters the end-of-
volume mark -- the same signal they use to indicate that you've just filled
up a file-system, duckie.)