Re: port-xen/59451: XEN3_DOM0 kernel finds the wrong root device

["Chuck Zmudzinski via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR port-xen/59451; it has been noted by GNATS.

From: Chuck Zmudzinski <frchuckz%gmail.com@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: port-xen/59451: XEN3_DOM0 kernel finds the wrong root device
Date: Mon, 2 Jun 2025 01:46:53 -0400

 On 6/1/2025 8:05 AM, Chuck Zmudzinski via gnats wrote:
 > The following reply was made to PR port-xen/59451; it has been noted by GNATS.
 > 
 > From: Chuck Zmudzinski <frchuckz%gmail.com@localhost>
 > To: gnats-bugs%netbsd.org@localhost
 > Cc: 
 > Subject: Re: port-xen/59451: XEN3_DOM0 kernel finds the wrong root device
 > Date: Sun, 1 Jun 2025 08:02:55 -0400
 > 
 >  On 6/1/2025 1:55 AM, Michael van Elst via gnats wrote:
 >  > The following reply was made to PR port-xen/59451; it has been noted by GNATS.
 >  > 
 >  > From: mlelstv%serpens.de@localhost (Michael van Elst)
 >  > To: gnats-bugs%netbsd.org@localhost
 >  > Cc: 
 >  > Subject: Re: port-xen/59451: XEN3_DOM0 kernel finds the wrong root device
 >  > Date: Sun, 1 Jun 2025 05:52:25 -0000 (UTC)
 >  > 
 >  > ...
 >  >  
 >  >  However, nothing of that really helps to use wedges ("dkXX") as
 >  >  wedge unit numbers are a bit volatile.
 >  >  
 >  >  
 >  >  The better alternative is to not set "bootdev" but to pass the
 >  >  "root" command line option. The value is a string and interpreted
 >  >  by the MI part of the kernel as a device name (with partition
 >  >  for a disk) or as NAME=wedgename (or for compatiblity wedge:wedgename).
 >  >  
 >  >  E.g.:
 >  >  
 >  >  menu=Boot Xen Dom0:load /netbsd_xen console=pc root=NAME=my-root;multiboot /xen.gz
 >  >  
 >  >  
 >  
 >  I think even in this code which is not in the MI part of the kernel the NAME= syntax
 >  for bootdev or rootdev is supported. I did try that but could not get a successful
 >  boot using NAME=wedgename.
 
 I tested again with root=NAME=wedgename form again and it does work, even without
 any kernel patches, but that is with a reduced length of the boot command I used in
 boot.cfg. I verified that it did not work in my previous try because my boot.cfg
 command line was too long, which include a long UUID plus long strings to specify
 com port settings for Xen. When I went to a shorter command line, the NAME=wedgename
 form for specifying the bootdev/root worked fine. The problem I noticed was the
 last characters of the wedgename (it was a UUID) were truncated unless I reduced
 the length of the command line in boot.cfg.
 
 Still, the bootdev=dk12 form needs some fix/kernel patch for this case when
 NetBSD/xen is installed on a wedge with a double digit index, so this PR should
 remain open.
 
 >  
 >  Also, according to a message I received on netbsd-users from Manuel who AFAIK is
 >  a port-xen maintainer, there is no difference in the arch/xen code between
 >  bootdev= and rootdev=. What you say here puts that in doubt, though.
 
 My testing verified that Manuel is correct: bootdev= and root= behave the same way,
 but actually root= is better because it gives me three more characters for the
 boot command line before it overflows and starts to truncate the end of the command
 line.
 
 Kind regards,
 
 Chuck Zmudzinski