Re: playing with bootxx_ext2fs

[pierre-philipp braun <pbraun%nethence.com@localhost>]

> A BSD disklabel will be on sector 1 if you create a filesystem that
> starts at 0.
> 
> I am not sure if you are talking about sector numbers of the disk, or of
> a partition.

I am talking about the netbsd/a9 DOS partition, and I am doing
`mkfs.ext2 -O^dir_index` all over it.  That partition starts either at
sector 63 or 2048 -- no additional problems there, both offsets behave
the same so far in terms of encountered issues.  And it ends +25G later
but I could also use the full 1TB disk (no big difference there so far
either).

> So that means you did get the MBR to read the chainload sector 0 of the
> partition (that you dd'd) and then the 2-13 or whatever, but then it
> could not deal with the fs.

Yes we got into the phase 1 boot strap.  It just does not know where to
find the (phase 2) netbsd boot loader.

> Here, I think we are lacking clarity on the plan for booting ext2, and
> that someone (you?) should figure that out, rather than guessing.

It is a learning process indeed.  Test&Try is one of the ways to
proceed;-)  But yes I obviously need more theory knowledge.

> You may be better off with FreeBSD as an installation base.

I will try building the ext2 fs from there.  Actually I am wondering if
the FreeBSD UFS and NetBSD ones could be somehow compatible.  As a
matter of fact I could validate that NetBSD FFSv2 could be mounted just
fine (and RW) from FreeBSD 11.1.

> You can also do a tools build for the rescue OS and copy nbdisklabel,
> nbinstallboot onto the rescue system and then run them.

Ok that is another another plan.

> You could also set up a disk that is laid out how you want the system to
> be, with a smallish (0.5G) root fs as wd0a.  And then in linux download
> that and write it to the disk.  So you'd have netbsd bootblocks and no
> grub.

Yes that would be an option and it could eventually scale across
different hardware models.  The rest of the partitioning and system prep
would be done/scripted on top of that smalling working root file-system.
Drawback it I would have to rebuild the full smallish disk image at
every NetBSD release, instead of just updating the deployment script.

I could use sysinst (as I am able to load a kernel) but that's far less
scalable as I would have to reach the crappy Java console every time to
proceed with the installation.

There is also miniroot.kmod which would maybe help me on this front.

> You mention grub, but I don't know why that's involved if this is bare
> metal, other than that it may be that's all you could write from the
> linux installer.

Exactly.  That's the only thing that works so far.  I finally heard
NetBSD/i386 may be MULTIBOOT compatible, though (and not only the XEN
dom0 flavor as a module).  I did not try that.

> So to understand, you or someone will have to really understand the
> ext2fs layout and the theory of how bootxx_ext2fs is supposed to be
> placed and how it is supposed to be run and then how /boot is supposed
> to be able to read ext2fs.

Yes