Re: How make boot loader or kernel on USB stick use another device as root FS, e.g. a BIOS-unsupported PCIe NVME SSD?

Hi Stuart, thanks a lot for responding -

The most relevant followup question is probably the one about
why not using boot.conf would work out, at the bottom.

> On 2018-02-01, tinkr@openmailbox.org <tinkr@openmailbox.org> wrote:
>> Hi, so, this question sprung from the previous email however it's a big
>> one and so deserves to be addressed separately:
>>
>> If a machine's BIOS does not support booting from a particular boot
>> medium where OpenBSD is installed, e.g. my BIOS does maybe not
>> supporting booting from PCIe NVME SSD:s, but it does support booting
>> from USB memory sticks.
>>
>> For such situations, how can I create an OpenBSD USB stick boot disk,
>> that continues the OpenBSD boot process for me but from the PCIe NVME
>> SSD-stored crypto softraid?
>>
>> This could be done either by
>>
>> * The OpenBSD kernel being stored on the USB stick, loading from it,
>> and then using the PCIe NVME SSD as both root disk, swap disk, and
>> dump disk, or,
>
> I think this should be possible with a custom kernel to set the
> devices. Updates will be annoying and it will be tough to get KARL
> to work nicely.

Wait what does KARL mean here?

And what's the kernel compile time setting, would this be a patch or
is there some define somewhere?

>> * The OpenBSD boot loader which is stored on the USB memory stick,
>> would load the OpenBSD kernel from the PCIe NVME SSD.
>
> The boot loader uses BIOS IO functions, if those can't talk to the
> NVME it's not going to work.

I'm not sure but I think that, while some BIOS:es will not do IO with
the PCIe NVME, then, I think my BIOS (and then of course some other
peoples') actually does provide access to the NVME SSD, it's just that
it won't boot from it.

I'd need to debug this much closer though.

>> This should be a fundamental and trivial usecase to OpenBSD, however,
>> last time I tried (then with adding a "boot" command to boot.conf per
>> http://man.openbsd.org/boot.conf ), I think it not worked out of the
>> box.
>
> It might not be very appealing but afaict the only trivial way to do
> this is to place root on the USB stick or some other device, and other
> filesystems on NVME.

boot.conf (http://man.openbsd.org/boot.conf) specifies in three or more
places, ways to change the boot disk.

First, do "boot hd1a:/bsd", next do "machine boot hd1a", next "set device hd1a".

Why would all of these three not be effective?

E.g. at completion of the OpenBSD installation do:

echo "set device hd1a" >> /mnt/etc/boot.conf
installboot -r /mnt sd1

(Here, sd1 is the OpenBSD installer USB memory stick, and, when
booting from it, hd0 would be the same USB memory stick, and hd1a would
be the PCIe NVME.)

Following up on this question in one more wider email shortly.

Tinker