kern/48870: Problem with disks larger than 2 TB in Xen

[marcotte%panix.com@localhost]

>Number:         48870
>Category:       kern
>Synopsis:       Problem with disks larger than 2 TB in Xen
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 04 18:45:00 +0000 2014
>Originator:     Brian Marcotte
>Release:        6.1.4
>Organization:
Public Access Networks, Corp.
>Environment:
NetBSD backup3.nyc.access.net 6.1.4 NetBSD 6.1.4 (PANIX-XEN-STD) #1: Tue Jun  3 
12:04:23 EDT 2014  
root%juggler.panix.com@localhost:/misc/obj/misc/devel/netbsd/6.1.4/src/sys/arch/i386/compile/PANIX-XEN-STD
 i386

>Description:
I'm having a problem with virtual disks larger than 2 TB.

A 3 TB virtual disk probes correctly:

        xbd12: 3072 GB, 512 bytes/sect x 6442450944 sectors

read/write appears to work correctly against the whole disk.

The problem is that the disklabel/gpt programs think the size is the
size modulo 2 TB. I would expect disklabel to max out at 2 TB, but in
this example, it's sees a 1 TB disk. So does gpt.

It looks like something is returning the size as a 32 bit number.

My dom0 is linux, and both dom0 and domU are 32 bit. Xen is 64 bit.

>How-To-Repeat:
Give a greater than 2 TB disk to a NetBSD/xen 32-bit domU. Try to
use "gpt" to partition the disk.

A sparse file is fine if actual large disks are not available.

>Fix: