From owner-freebsd-current  Wed Mar 17  4:55:21 1999
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From: Robert Nordier <rnordier@nordier.com>
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Subject: Re: How to add a new bootdevice to the new boot code ???
In-Reply-To: <199903171116.MAA25664@freebsd.dk> from =?ISO-8859-1?Q?S=F8ren_Schmidt?= at "Mar 17, 99 12:16:49 pm"
To: sos@freebsd.dk (Søren Schmidt)
Date: Wed, 17 Mar 1999 14:49:50 +0200 (SAT)
Cc: current@FreeBSD.ORG
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> > I assume at some stage that some stage the new driver will take over
> > completely, and the older driver will disappear.  Before that, as
> > people grow accustomed to thinking "ad" rather than "wd", it will
> 
> Not likely, as long as we need support for MFM/RLL/ESDI disk, wd.c
> will stay around.
> 
> > probably make sense for the boot code to accept (say)
> >
> >     0:ad(0,a)boot/loader
> > 
> > rather than
> > 
> >     0:wd(0,a)boot/loader
> 
> That would be nice, could I please have that ??

OK, I'll add it to the bootblocks.

Incidentally, while I'm in there and thinking about it, I'd quite
like to fix the boot code to boot from LS-120 drives at the same
time.  So if anyone has one of these, and wouldn't mind spending
some time running a few bits of test code, I'd appreciate it.

> > However, I'd *still* expect it to pass a major# of 0 rather than
> > 30.  Why?  Because a 2.0 kernel knows only 0.  And if a 5.0 kernel
> > knows only 30, it is -- at least -- in a position to know what
> > 0 meant, and simply substitute one for the other (under the
> > influence of a kernel configuration option, if necessary).
> 
> Hmm, wd should give 0 and ad should give 30, no AI please :)

I wasn't actually thinking at all along the lines of "smart" code
at all:

    #ifdef FORCE_FOO
	if (foo == 0)
	    foo = 30;
    #endif

The administrator or operator is still entirely in control; the
only difference is in what part of the code the control is exercised.

AFAICS, adopting the separate "wd" and "ad" route entails the
following:

    Update your bootblocks.
    Add a /boot.config statement like "0:ad(0,a)" to make use
    of the driver the default.
    Failure to boot if you inadvertently specify wd out of habit,
    or if you specify ad when booting an earlier system.

So we're introducing three points with good potential for failure.

In contrast, the kernel configuration route requires commenting
or uncommenting a single statement.

-- 
Robert Nordier


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