---Problem Description---
Specifying serial number on a virtio-block backed disk (via <serial> tag in XML) does not work.

---uname output---
Linux alaska.linuxperf9025.net 2.6.32-71.el6.x86_64 #1 SMP Wed Sep 1 01:33:01 EDT 2010 x86_64 x86_64
x86_64 GNU/Linux

Machine Type = System Information Manufacturer: IBM Product Name: BladeCenter HS22V
-[7871AC1]- Version: 02

---Steps to Reproduce---

Create RHEL6.0 Guest (on RHEL6.0 host) with virtio-block virtual disk (or alternatively use the
virsh attach-device command to add later) specifying a serial number for the disk via the <serial>
tag.

Once the guest is started one should be able to view the serial number for this virtual disk in
/dev/disk/by-id.

No serial number is being propogated through to /dev/disk/by-id.

[root@localhost ~]# ls /dev/disk/by-id/
dm-name-VolGroup-lv_root
dm-name-VolGroup-lv_swap
dm-uuid-LVM-gKyZKm5h3jr0gwsvKGyNpnJM4a3NlqlEdNV7INjcLs9lVxOAml5ETPkWga2zuWHZ
dm-uuid-LVM-gKyZKm5h3jr0gwsvKGyNpnJM4a3NlqlEtvDt4W1c7ZONUKN4W8U6MWT2qYVjglie

Note: <serial> does work for IDE backed disks,
Note: It doesn't require attach-device. Just hand-editing a shutdown guest XML and restarting would
exhibit this problem as well.

Attachments:
- Guest XML (post creation/start) from virsh dumpxml
- XML used to 'attach' new disk via virsh attach-device. Specifies <serial> number for disk.
- DumpXML of guest after 'virsh attach-device rhel6vm1 att.xml'