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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.os.linux.development.system,comp.unix.bsd.386bsd.misc,comp.unix.bsd.bsdi.misc,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc,comp.os.linux.advocacy
Subject: Re: Historic Opportunity facing Free Unix (was Re: The Lai/Baker paper, benchmarks, and the world of free UNIX)
Date: Wed, 17 Apr 1996 18:55:33 -0700
Organization: Me
Lines: 63
Message-ID: <3175A115.357EC1E5@lambert.org>
References: <4ki055$60l@Radon.Stanford.EDU> <31702487.420C2193@lambert.org> <yfg3f67giw7.fsf@time.cdrom.com> <31718ED3.555EB900@lambert.org> <4l33ls$416@helena.MT.net>
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Nate Williams wrote:
]
] In article <31718ED3.555EB900@lambert.org>,
] Terry Lambert <terry@lambert.org> wrote:
] >] Now let's talk about "magic install images". Such an image is
] >] a non-memory-overcommit (fd's are not strictly recoverable for
] >] executables) APM save image of a sytem "just about to be
] >] installed".
] >]
] >] I'd need to see a prototype of this before I could even begin to
] >] believe there weren't 500 different "gotchas" still waiting to
] >] spring on the unwary implementor.
] >
] >Nate Williams already has a prototype. It's called the APM code
] >from the "BSD Nomads" group in Japan, and his own contributions
] >to the APM code and source integration.
] >
] >Fundamentally, there is no difference betwen restoring machine
] >state from a disk image of saved state of the same machine, and
] >that of a different machine.
]
] Umm, just to let everyone know (Terry and I already had this
] discussion in private email), the code I wrote plus the code
] from the Nomad doesn't contain any way of restoring the 'state'
] of the system from a disk image. Some laptops have this
] feature (an older IBM ThinkPad does, and my newer NEC Versa
] doesn't), but it's not part of the 'official' APM specification.
] IBM provides a driver to do this under DOS/Windows 3.1,
] but no such driver exists for WNT/Win95, so this isn't
] possible w/out manufacturer support under other OS's.
Again from the private exchange, this is a confusion on my part
between PM (Power Management, the general idea) and APM (the
specification).
Nate and I agreed that APM only provides a portion of the design
needed for a full implementation of PM.
Most of the information required for state save/restore on most
processors exists in the Van Gilluwe book "The Undocumented PC",
and involves ICEBP on Intel and IBM processors, and similar
processer state dump/restore instructions for those vendors
who didn't do real Intel chip clones. There are about six
implementations, total.
Conceptually, state save and recovery is no more difficult
an idea than the "cracking cartridges" for Commodore 64 and
Atari computers (which dumped an image of the running machine
state along with some state restore code to a floppy after
the copy protection verification took place). Similar cards
were eventually sold for PC's, which ended up driving the
final nail in the coffin of sofware copy protection.
I'm not claiming it's a new idea, only that it's time.
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.