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: 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)
 > 
 >  frchuckz%gmail.com@localhost writes:
 >  
 >  >--- sys/arch/xen/xen/xen_machdep.c.orig 2023-10-18 12:53:03.000000000 -0400
 >  >+++ sys/arch/xen/xen/xen_machdep.c      2025-05-30 20:42:39.936253878 -0400
 >  >@@ -553,7 +553,10 @@
 >  >                        /* XXX check device_cfdata as in x86_autoconf.c? */
 >  >                        booted_partition = toupper(
 >  >                                xcp.xcp_bootdev[strlen(devname)]) - 'A';
 >  >+                       /* Check that the value of booted_partition is sane */
 >  >+                       if (booted_partition & 0xfffffff0)
 >  >+                               continue;
 >  >                        DPRINTF(("%s: booted_partition: %d\n", __func__, booted_partition));
 >  >                }
 >  >                booted_device = dv;
 >  
 >  
 >  The code should check that the partition is between 0 and MAXPARTITIONS-1
 >  instead of using some bitmask and it shouldn't touch booted_partition
 >  before the value is validated.
 
 I agree the actual fix should verify booted_partition using MAXPARTITIONS.
 And YES I agree that booted_partition should not be touched before it is
 validated. Even the current, unpatched code has that problem!
 
 >  
 >  It should also parse xcp_bootdev better (this was bad before and the
 >  x86 version of that code isn't really better).
 
 YES again!
 
 >  
 >  
 >  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.
 
 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.
 
 Do you want me to try NAME=wedgename again using root= instead of bootdev= ?
 
 Kind regards,
 
 Chuck