port-xen/46836: cannot change memory in domU via balloon

[agrier%poofygoof.com@localhost]

>Number:         46836
>Category:       port-xen
>Synopsis:       cannot change memory in domU via balloon
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Aug 25 07:30:10 +0000 2012
>Originator:     agrier%poofygoof.com@localhost
>Release:        NetBSD 6.0_BETA2
>Organization:
  Aaron J. Grier | "Not your ordinary poofy goof." | 
agrier%poofygoof.com@localhost
>Environment:
System: NetBSD theano.pythagoras.poofy.goof.com 6.0_BETA2 NetBSD 6.0_BETA2 
(XEN3PAE_DOMU) #1: Fri Jun 1 00:11:53 PDT 2012 
agrier%pythagoras.poofy.goof.com@localhost:/disk/teraraid/obj/i386/disk/teraraid/NetBSD/6/src/sys/arch/i386/compile/XEN3PAE_DOMU
 i386
Architecture: i386
Machine: i386

dom0 is running NetBSD 6.0_BETA2 on amd64 built from similarly-dated
sources.
>Description:
the xen balloon driver in domU does not appear to be able to request a
change in memory.

this works in linux with a stock fedora 17 kernel 3.5.2, IE 'echo
$NEWMEMSIZE > /sys/devices/system/xen_memory/xen_memory0/target' within
a linux domU will change the amount of memory the domU is using.
>How-To-Repeat:
# sysctl -w machdep.xen.balloon.target=1048576  
machdep.xen.balloon.target: 2621440 -> 1048576
# dmesg | tail -1
balloon0: error 13, couldn't write xenbus target node
>Fix: