1 Jan
2023
1 Jan
'23
2:02 a.m.
On 31 Dec 2022, at 15:59, Dan Cross
<crossd(a)gmail.com> wrote:
On Fri, Dec 30, 2022 at 1:26 PM Paul Ruizendaal <pnr(a)planet.nl> wrote:
That is interesting. Are you referring to this:
https://www.tuhs.org/cgi-bin/utree.pl?file=4.1cBSD/a/sys/conf
https://www.tuhs.org/cgi-bin/utree.pl?file=4.1cBSD/usr/man/man8/config.8
Or is auto configuration something else?
[snip]
It would seem that the next step for Unix in the area of boot, config and device drivers
came with Sun’s OpenBoot in 1988 or so. This also appears to be the first appearance of
device trees to describe the hardware to the bios and the kernel. Moreover, it would seem
to me that OpenBoot is a spiritual ancestor of the modern Risc-V SBI specification. Maybe
by 1988 the IO hardware had become sufficiently complex and/or diverse to warrant a break
from tradition?
Was there any other notable Unix work on better organising the boot process and the
device drivers prior to OpenBoot?
I think that BSD supported autoconfiguration on the VAX well before
OpenBoot; the OpenBSD man page says it dates from 4.1 (1981) and was
revamped in 4.4. SBI was/is an attempt to define a common interface to
different
devices using RISC-V CPUs, but it's growing wildly and tending more
towards UEFI+ACPI than something like OpenBoot, which was much
simpler.
In general, the idea of a BIOS isn't terrible: provide an interface
that decouples the OS and hardware. But in practice, no one has come
up with a particularly good set of interfaces yet. Ironically,
BSD-style autoconfig might have been the best yet.
When it comes to abstracting devices, it would seem to me that virtio has gotten quite
some traction in the last decade.
Looking at both the systems of 40 years ago and the Risc-V SoC’s of last year, I could
imagine something like:
- A simple SBI, like the Berkeley Boot Loader (BBL) without the proxy kernel & host
interface
- Devices presented to the OS as virtio devices
- MMU abstraction somewhat similar in idea to that in SYSV/68 [1]
Together this might be a usable Unix BIOS that could have worked in the early 80’s. One
could also think of it as a simple hypervisor for only one client. The remaining BBL
functionality is not all that different from the content in mch.s on 16-bit Unix (e.g.
floating point emulation for CPU’s that don’t have it in hardware). A virtio device is not
all that different from the interface presented by e.g. PDP-11 ethernet devices (e.g.
DELUA), the MMU abstraction was contemporary.
High end systems could have had device hardware that implemented the virtio interface
directly, low end systems could use simpler hardware and use the BIOS to present this
interface via software.
[1] From mmu.h in the SYSV/68 source tree:
/*
@(#)mmu.h 2.26
This is the header file for the UNIX V/68 generic
MMU interface. This provides the information that
is used by the various routines that call:
mmufork ()
mmuexec ()
mmuexit ()
mmuread ()
mmuwrite ()
mmuattach ()
mmudetach ()
mmuregs ()
mmualloc ()
mmuinit ()
mmuint ()
The above routines and secondary routines called
by them are contained in io/mmu1.c and io/mmu2.c.
*/