The serial property of -drive will be deprecated in RHEL7.  I don't think this bug is important enough to fix.

Please check that specifying a serial number with libvirt and type='lun' gives an error, though.

(In reply to Paolo Bonzini from comment #2)
> The serial property of -drive will be deprecated in RHEL7.  I don't think
> this bug is important enough to fix.
> 
> Please check that specifying a serial number with libvirt and type='lun'
> gives an error, though.
Also tried as your instructor but still can boot up guest without any error message prompt if specify a serial number with libvirt and type='lun', and the passthrough disk worked well in guest.

xml example:
...
<disk type='block' device='lun'>
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/dev/disk/by-path/ip-10.66.90.100:3260-iscsi-iqn.2001-05.com.equallogic:0-8a0906-6eb1f7d03-30cf49b25f24f94d-libvirt-1-150313-lun-0'/>
      <target dev='sdd' bus='scsi'/>
      <serial>WD-WMAP9A966149</serial>
      <address type='drive' controller='0' bus='0' target='0' unit='3'/>
   </disk>
   <controller type='scsi' index='0' model='virtio-scsi'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
   </controller>
...

# ps axu | grep qemu-kvm
...-device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x8 -drive file=/dev/disk/by-path/ip-10.66.90.100:3260-iscsi-iqn.2001-05.com.equallogic:0-8a0906-6eb1f7d03-30cf49b25f24f94d-libvirt-1-150313-lun-0,if=none,id=drive-scsi0-0-0-3,format=raw,serial=WD-WMAP9A966149,cache=none -device scsi-block,bus=scsi0.0,channel=0,scsi-id=0,lun=3,drive=drive-scsi0-0-0-3,id=scsi0-0-0-3

Best Regards,
sluo

This bug was not selected to be addressed in Red Hat Enterprise Linux 6. We will look at it again within the Red Hat Enterprise Linux 7 product.

Guess I should have looked through this bug more closely a while ago...

Anyway, even though -serial was deprecated and providing it doesn't seem to harm anything, I've posted a patch upstream in order to cause an error from libvirt:

http://www.redhat.com/archives/libvir-list/2015-June/msg00388.html

Patch pushed upstream:

commit 4fce9e84798be1441d8bc5b96f0ed68589e85222
Author: John Ferlan <jferlan>
Date:   Tue Jun 9 16:49:00 2015 -0400

    qemu: Do not support 'serial' scsi-block 'lun' devices
      
    Seems the property has been deprecated for qemu, although seemingly ignored.
    
    This patch enforces from a libvirt perspective that a scsi-block 'lun'
    device should not provide the 'serial' property.

$ git describe 4fce9e84798be1441d8bc5b96f0ed68589e85222
v1.2.16-149-g4fce9e8

I can reproduce it with libvirt-1.2.16-1.el7.x86_64. and verify it like following: 

verify version:
libvirt-1.2.17-5.el7.x86_64
qemu-kvm-rhev-2.3.0-18.el7.x86_64

verify steps:
check formatdomain.xml:
1.open 
file:///usr/share/doc/libvirt-docs-1.2.17/html/formatdomain.xml
serial
Not supported for scsi-block devices, that is those using disk type 'block' using device 'lun' on bus 'scsi'.

check define start and hot plug :
1.define start a guest has a scsi-block lun device with serial. 

# virsh dumpxml r708 | grep disk -A 8
 <disk type='block' device='lun'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/disk/by-path/ip-$IP:3260-iscsi-iqn.2008-09.5.165.3ffe.104:server.target3-lun-1'/>
      <target dev='sda' bus='scsi'/>
      <serial>WD-WMAP9A966149</serial>
      <address type='drive' controller='0' bus='0' target='3' unit='0'/>
    </disk>
#virsh start r708

error: Failed to start domain r708
error: unsupported configuration: scsi-block 'lun' devices do not support the serial property

2.hot plug  attach-disk / attach-device

2.1 prepare a disk xml like following :
# cat blk-lun-scsi.xml 
<disk type='block' device='lun'>
<driver name='qemu' type='raw'/>
<source dev='/dev/disk/by-path/ip-10.66.5.165:3260-iscsi-iqn.2008-09.5.165.3ffe.104:server.target3-lun-1'/>
<serial>WD-WMAP9A966149</serial>
<target dev='sda' bus='scsi'/>
<address type='drive' controller='0' bus='0' target='3' unit='0'/>
</disk>

# virsh attach-device r708 blk-lun-scsi.xml 
error: Failed to attach device from blk-lun-scsi.xml
error: unsupported configuration: scsi-block 'lun' devices do not support the serial property

2.2 attach-disk with --serial for scsi-block device.

#lsblk
......
sdc                                                   8:32   0    30G  0 disk  
...

# virsh attach-disk r708 /dev/sdc sdb --sourcetype block --type lun --targetbus scsi --serial WD-WMAP9A966149
error: Failed to attach disk
error: unsupported configuration: scsi-block 'lun' devices do not support the serial property

attach block-scsi 'disk' device is successful.
# virsh attach-disk r708 /dev/sdc sdb --sourcetype block --type disk --targetbus scsi --serial WD-WMAP9A966149
Disk attached successfully

now, scsi-block lun device do not support the serial property. move to verified.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2202.html

Now bug 1291930 is asking whether this tightening of the parse to reject something that was previously ignored is a regression. :(