pkg/42912: Xen HVM guests detect a 0 MBytes hard disk in some situations (QEMU related?)

[hugo%barafranca.com@localhost]

>Number:         42912
>Category:       pkg
>Synopsis:       Xen HVM guests detect a 0 MBytes hard disk in some situations 
>(QEMU related?)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Mar 02 14:25:00 +0000 2010
>Originator:     Hugo Silva
>Release:        NetBSD 5.99.24
>Organization:
>Environment:
NetBSD 5.99.24 NetBSD 5.99.24 (XEN3_DOM0) #0: Sun Feb 28 19:27:54 WET 2010  
root@:/usr/obj/sys/arch/amd64/compile/XEN3_DOM0 amd64
>Description:
QEMU detects a 0 MBytes hard disk in certain situations (see below), rendering 
the virtual machine (Xen HVM guest) unusable.

xentools33-3.3.2nb2 Userland Tools for Xen 3.3.x
xenkernel33-3.3.2   Xen 3.3.2 Kernel

-----
/dev/wd5d: (doesn't work)
xbd backend: attach device wd5d (size 2930277168) for domain 10

qemu: could not open vbd '/local/domain/10/device/vbd/768/phantom_vbd' \
or hard disk image '/dev/wd5d' (drv 'phy' format 'raw')
-----

-----
/dev/rwd5d: (works)
xbdback backend/vbd/11/768: unknown device 0x353 (major=3)

nothing in the qemu log.
-----

-----
/dev/mapper/testvg0-freebsd0: (doesn't work)
xbdback backend/vbd/7/768: can't VOP_OPEN device 0xa908: 16

qemu: could not open vbd '/local/domain/7/device/vbd/768/phantom_vbd' \
or hard disk image '/dev/mapper/testvg0-freebsd0' (drv 'phy' format 'raw')
-----

-----
/dev/mapper/rtestvg0-freebsd0: (doesn't work)
xbdback backend/vbd/8/768: unknown device 0xc208 (major=194)

nothing in the qemu log.
-----
>How-To-Repeat:
Try to use Xen HVM guest with an equivalent of:

disk =  [
    'phy:/dev/mapper/testvg0-freebsd0,hda,w',
    'file:/tmp/8.0-RELEASE-amd64-disc1.iso,hdc:cdrom,r'
    ]

Then launch the VM.
>Fix: