Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ll-xn!mit-eddie!bloom-beacon!gatech!udel!rochester!pt.cs.cmu.edu!cadre!pitt!amanue!jr
From: jr@amanue.UUCP (Jim Rosenberg)
Newsgroups: comp.sys.att
Subject: Re: 3b1 3.51a kernel
Message-ID: <270@amanue.UUCP>
Date: 14 Apr 88 06:53:28 GMT
References: <1603@lll-lcc.aRpA> <339@icus.UUCP>
Reply-To: jr@amanue.UUCP (Jim Rosenberg)
Organization: Amanuensis Inc., Grindstone, PA
Lines: 33
Keywords: 3b1 3.51a fix disk unixpc

In article <339@icus.UUCP> lenny@icus.UUCP (Lenny Tropiano) writes:
>|>This brings up another question, has anyone or can you build a bootable
>|>floppy which you can run, of course, a minimal system under?  [...]
>
>Yeah, I been experimenting with this with minimal luck.  I know that the
>".vl and .sl" extentions on the fdfmt and fdfmt10 command create floppies
>with the system loader on it.  I've booted them with a copy of /unix and
>other stuff and it still seems to want to boot off the hard disk.

I haven't played with this on a 3b1, but did make bootable floppies for Venix
on a PC-type machine, & I believe the principle is the same.  Your kernel
(/unix) has "wired" into it rootdev, pipedev, and swapdev -- at least that's
what they are on some systems.  These are direct references into the device
switch table, if I'm not mistaken.  Copying /unix from your hard disk onto a
file system on a floppy will *definitely* have these set for the hard disk.
On systems with configuration rights (I think the going phrase these days is
"Link Kit") you have to make a new kernel to get these to recognize the floppy
instead of the hard disk.  On some systems this is all in /usr/sys/conf/c.c,
if my memory is still intact.

None of this helps a bit for the 3b1.  Don't we get some kind of tunable
parameters?  Hmm.  /etc/lddrv/unix.sym has values for rootdev, pipedev, and
swapdev.  One might be able to sdb a copy of /unix and just change these.
***CAREFUL*** though, I see lots of other symbols in there that don't look too
familiar that might need to be changed too.

Of course the *easy* way is to snarf the kernel from a floppy that's already
bootable.  Has anyone tried mounting one of the bootable floppies and rooting
around for a kernel?
-- 
 Jim Rosenberg
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