Subject: Re: VPS mailing list, BSD interest?
To: None <email@example.com, tech-kern@NetBSD.ORG>
From: der Mouse <mouse@Holo.Rodents.Montreal.QC.CA>
Date: 10/03/1996 09:25:47
> How can you have an LFS root partition (never mind the LVM stuff),
> and still be able to boot on, say, a Sun3?
Perhaps you can't, which would mean only that you can't have an LVM
root on a sun3.
> I mean, doesn't the boot prom have to be able to read the file system
> to load the loader program?
> Where are you going to stuff boot.sun3?
Now, I don't know about other machines, but the sun3 I do know a bit
about. (This also is true of the sparc, at least all sparcs I've ever
looked at the boot mechanisms of.)
The PROMs know enough about the disklabel to locate the start of the
desired boot partition. They then load a bootstrap from the beginning
of that partition (sectors 1 through 15, IIRC) and hand control over to
The PROMs don't know a thing about the filesystem. That knowledge is
all in later-stage bootblocks. In the NetBSD paradigm (and in more
recent SunOS - 3.5 was the last SunOS I used that didn't work this
way), the bootblock loaded by the PROM just has a list of disk block
numbers wired into it, set by installboot when the bootblock was
installed. It loads these blocks, trusting that they're the correct
ones. _That_ program knows enough about the filesystem to load /netbsd
(/vmunix under SunOS).
In short, provided we stick with mostly-SunOS disklabels, the sun3 and
sparc ports can use damn near anything for a root filesystem layout, as
long as someone writes bootblocks that can grok it.
01 EE 31 F6 BB 0C 34 36 00 F3 7C 5A C1 A0 67 1D