Date: Mon, 13 Aug 2001 03:24:57 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Bernd Walter <ticso@mail.cicely.de> Cc: Matthew Jacob <mjacob@feral.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: mtio questions Message-ID: <3B77AAF9.E5121435@mindspring.com> References: <20010812140406.A7326@cicely20.cicely.de> <Pine.BSF.4.21.0108121753040.65085-100000@beppo> <20010812140406.A7326@cicely20.cicely.de> <3B76CF21.C6915AB0@mindspring.com> <20010813105830.A10524@cicely20.cicely.de>
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Bernd Walter wrote:
>
> On Sun, Aug 12, 2001 at 11:46:57AM -0700, Terry Lambert wrote:
> > Bernd Walter wrote:
> > > Another point:
> > > Can we '#define MTEOM MTEOD' as MTEOM is used on NetBSD and Solaris?
> >
> > "End of Message" is not the same as "End of Data" for some
> > drives; this could break old 8-track (no, not the music, and
> > not a typeo for "9-track"!) drives, e.g. Zilog and Cypher.
>
> Well that's what Solaris 8 sys/mtio.h tells about MTEOM:
> #define MTEOM 10 /* position to end of media */
> And here NetBSD 1.5:
> #define MTEOM 10 /* forward to end of media */
>
> Neither of them is saying "Message".
I was thinking "Media", but wrote "Message", since that's what
the ASCII characer EOM means; my bad.
The "end of the media" can be interpreted as "after the first
EOF, before the second, in order to permit the tape volume to
be extended".
It can also be interpreted to mean "before the first of two EOFs,
such that the last extent can be extended".
It's really hardware dependent, and ambiguous.
> Please correct me if I'm wrong:
> If I want to append to a tape I would MTEOM on Solaris and MTEOD on
> FreeBSD so it's supposed to be used for the same reason.
> None of the OS I looked into had both.
>
> But well - that's what HP-UX define:
> #define MTEOD 8 /* DDS, QIC and 8MM only - seek to end-of-data */
These devices are not absolutely positionable to EOM; they
leave you "after the last data block"; on QIC, which records
like:
------->--------------->------------->--------.
,-------------------------------------------+--.
`-------------------------------------------' |
-------------------------------------------------'
It's nearly impossible to position to an exact location.
DEC MT-50, MT-75, and 9-Track drives, on the other hand, were
abosolutely positionable, and often were written with a real
filesystem on them (FILES-11 format instead of ANSI format).
You are delving into an area where things vary widely by vendor
and the crossproduct of drivers and hardware...
-- Terry
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