Re: annual HOWTO rampage, mini edition

[Greg Troxel <gdt%lexort.com@localhost>]

"Greg A. Woods" <woods%planix.ca@localhost> writes:

>>   How do you tell the system to use PVH for dom0?  Changing /boot.cfg?
>>   Just boot GENERIC instead of XEN3_DOM0?
>
> Yes, just add "dom0=pvh" to the xenkernel command-line in /boot.cfg.

Thanks, added.

> However relevant to updating the HOWTO, I wrote this:
>
>> BTW, there's a pile of BS, aka "fake news", written about xencons(4) in
>> the Xen HowTo on the wiki.  I'll write separately about that, again.

No need to be perjorative.  It should be obvious that all of this was
written in good faith, even if there is a bit of "guess slightly and
wait for corrections, because when you ask for contributions none
arrive".  Some of this text is ancient; I started using NetBSD/xen in
2005 and it predated my use.

> So, first off, xencons(4) has nothing whatsoever to do with the Xen
> kernel's messages.  (yes, "xl dmesg" is how to see them)

I'm having trouble following this.  On my dom0 (NetBSD 10, pretty normal):

  xencons0 at hypervisor0: Xen Virtual Console Driver
  vga0 at pci0 dev 2 function 0: Intel 82G45 Integrated Graphics Device (rev. 0x03)
  wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100 emulation)
  wsmux1: connecting to wsdisplay0

which says the dom0 kernel is using wsdisplay0 as the console.  That
later makes sense in the vga case.

So is there some hypercall to get the xen messages and that is what
happens with xl dmesg?  And a dom0 kernel w/o any kind of console can
still do that?

> Secondly xencons(4) _is_ in fact the default console(4) device for
> NetBSD/XEN3_* kernels, and in fact it is the _correct_ console to use
> for a dom0 with a serial console (console=com0 is _never_ better -- just
> let the hypervisor manage the com port!), and for _all_ NetBSD/XEN_DOMU
> domUs (it is what you connect to with "xl console domU" or "xl create -c
> domU.conf", and the constty login will appear there via xencons(4)).

For domU, agreed.

> However xencons(4) is _not_ useful for a NetBSD/XEN3_DOM0 with a VGA
> console (as you can't "xl console Domain-0" from dom0 even if that were
> somehow useful).  There you need/want "console=pc" on the NetBSD kernel
> command line (unless you have the iDrac problem, then you're basically
> without a dom0 console, ever).

Agreed and it more or less said that.

I did some rototilling.  Specific 'this is wrong; say that instead" is
welcome.   I'd appreciate comments even if confirming from others.