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From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
To: tuhs@minnie.tuhs.org
Cc: jnc@mercury.lcs.mit.edu
Subject: Re: [TUHS] Fwd: Choice of Unix for 11/03 and 11/23+ Systems
Date: Mon, 12 Oct 2020 18:43:26 -0400 (EDT)	[thread overview]
Message-ID: <20201012224326.51A1618C0E7@mercury.lcs.mit.edu> (raw)

    > From: Paul Riley

    > port Mini-Unix will create some demand for device drivers on the /03
    > systems, so may be worthwhile to implement RAW device.

I'm not sure I understand this ("worthwhile to implement RAW device"); let me
explain what the removal of 'raw' I/O devices from MINI-UNIX really means, and
then ask what it is that you are after.


Early Unix (no idea about later ones) supports two classes of devices; 'block'
devices, which can be used to hold file-systems, and 'character' devices,
which cannot. (I seem to recall a paper, perhaps from the Unix BSTJ issue,
which talks about them in some detail.)

The former are those where the underlying physical device has restricted
semantics; they are block-addressable mass storage devices. All access to them
is via the system's block buffer pool, so reads/writes by the user of
arbitrary size and location are possible. 'Character' devices are everything
else.

'Raw' devices are an interface to the devices of 'block' devices which does
not go through the system's buffer pool; I/O operations to them perform DMA
directly to the user process' memory. They are 'character' devices, in the
Unix device taxonomy. The only semantics available are those supported by the
hardware - e.g. seeks only to block boundaries.

So when I say that MINI-UNIX doesn't have 'raw' devices, it just means that
e.g. the RK disk controller device _only_ talks to the Unix block buffer
system; if a user program wants to look at the disk contents, it has to go
via that system.


So, with that in hand, what exactly is the need you forsee for raw devices
in MINI-UNIX?

Also, I've started to work on getting the V6 RL driver to work in MINI-UNIX;
it should have been easy (just delete the charater device interface), but
for some reason it didn't work when I tried it. I'll look at it in more
detail 'soon'.

       Noel

             reply	other threads:[~2020-10-12 22:44 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 22:43 Noel Chiappa [this message]
  -- strict thread matches above, loose matches on Subject: below --
2021-02-03  1:25 Noel Chiappa
2020-10-18 21:36 Norman Wilson
2020-10-12 19:27 Noel Chiappa
2020-10-10 23:29 Noel Chiappa
2020-10-11  2:30 ` Jay Logue
2020-10-11 23:24 ` Paul Riley
2020-10-12  0:53   ` Dave Horsfall
2020-10-12  1:56     ` Warner Losh
2020-10-12  2:09       ` Andrew Warkentin
2020-10-12 16:57       ` Arthur Krewat
2020-10-18 20:42     ` Michael Huff
2020-10-08 23:49 Noel Chiappa
2020-10-08 16:06 Noel Chiappa
2020-10-06 23:08 Noel Chiappa
2020-10-07  5:24 ` Jay Logue
2020-10-06 20:34 Noel Chiappa
2020-10-06 19:34 Noel Chiappa
2020-10-06 19:04 Noel Chiappa
2020-10-06 14:46 Noel Chiappa
2020-10-06 16:22 ` jay-tuhs9915
2020-10-02  0:39 Noel Chiappa
2020-10-01 12:51 Noel Chiappa
2020-10-02  0:23 ` Paul Riley
2020-09-30 23:16 Noel Chiappa
2020-09-30 18:51 Noel Chiappa
2020-09-30 17:58 Noel Chiappa
2020-09-28 23:21 Noel Chiappa
2020-09-30  1:50 ` Paul Riley
2020-09-27 21:07 Noel Chiappa
2020-09-27 21:12 ` Warner Losh
2020-09-28  0:22   ` Pete Turnbull
2020-09-27 20:50 Noel Chiappa
2020-09-29 13:20 ` Paul Riley
2020-09-25 22:08 Noel Chiappa
2020-09-26 14:52 ` John Foust
2020-09-28  0:03 ` Paul Riley
2020-09-28  0:06   ` Paul Riley
2020-09-24 18:56 Noel Chiappa
2020-09-24 13:04 Noel Chiappa
2020-09-24 18:24 ` John Cowan
2020-09-24 11:02 Paul Ruizendaal
2021-02-03  0:12 ` Greg A. Woods
2020-09-24  1:28 Noel Chiappa
2020-09-23 23:14 Noel Chiappa
2020-09-24  1:09 ` John Foust
2020-09-22 21:51 John Foust
2020-09-22 21:36 Noel Chiappa
2020-09-22 21:46 ` Warner Losh
2020-09-22 21:49 ` John Foust
2020-09-22 15:59 Noel Chiappa
2021-02-03  0:07 ` Greg A. Woods
2020-09-22  0:47 Noel Chiappa
2020-09-21 19:37 Noel Chiappa
2020-09-21 23:16 ` devin davison
2020-09-21 18:13 Noel Chiappa
2020-09-21 17:59 Noel Chiappa
2020-09-21 18:18 ` Arthur Krewat
2020-09-20 13:12 Noel Chiappa
2020-09-19 15:28 Noel Chiappa
2020-09-21 10:26 ` Paul Riley
2021-01-24 16:07 ` Tom Ivar Helbekkmo via TUHS
2021-01-25  4:58   ` Gregg Levine
2021-01-25  8:21     ` Tom Ivar Helbekkmo via TUHS
     [not found] <CAD05_j1bc6DDRtfPkd4QVeWXjwSp73bty46D=2ATozUbHThBWw@mail.gmail.com>
2020-09-19  3:22 ` Paul Riley
2020-09-19 14:20   ` Heinz Lycklama
2020-09-21 13:54     ` Paul Riley
2020-09-21 15:30       ` Heinz Lycklama
2020-09-21 23:27   ` Henry Bent
     [not found]     ` <4C35E6D2-8ABD-4DC2-BB2F-F15FA5BF30DD@icloud.com>
2020-09-22  0:22       ` Henry Bent

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