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Date:      Sun, 5 Jul 1998 19:11:38 +0000 (GMT)
From:      Terry Lambert <tlambert@primenet.com>
To:        julian@whistle.com (Julian Elischer)
Cc:        hackers@FreeBSD.ORG, sos@FreeBSD.ORG
Subject:   Re: block device on wst device.
Message-ID:  <199807051911.MAA26965@usr08.primenet.com>
In-Reply-To: <Pine.BSF.3.95.980704135433.10069E-100000@current1.whistle.com> from "Julian Elischer" at Jul 4, 98 01:58:28 pm

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> ther is a block interface to wst
> 
> is this used by anyone?
> does it work?
> 
> I think the block interface should go away
> as it doesn't really make much sense on tapes.
> (same for wt.c)
> 
> In effect it went a way some time ago for st.c

I still see this as a problem, specifically for tape devices.

I see the block device for tape drives capable of providing a kernel
side buffer that is not statically allocated to a particular driver
and which provides bufferring for streaming tape devices.

The examples I can come up with where the user space write to the
buffer should return immediately so that the user space program
can read, and therefore overlap physical tape and disk I/O, are
DAT devices and QIC-40/80/120/etc. devices.

This is specifically relevent to the FT (QIC-40/etc.) devices
because of there use of a (normally) non-FIFO-ed serial interface,
to wit, the floppy controller.

Some people will say "yeah, but no one with any sense uses those";
however, I could make the same argument against IDE on the same
basis (specifically, number of tagged commands drives allow in
their queues).  For a destop machine, cheap is often good enough,
and FT drives are certainly cheap.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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