Description of problem:
When selinux is enforcing, update floppy disk on the fly with <readonly/> failed with error
error: Failed to update device from floppy.xml
error: internal error unable to execute QEMU command 'change': Could not open '/var/lib/libvirt/images/fd2.img'

but when selinux is permissive, update-device will success

Version-Release number of selected component (if applicable):
kernel-2.6.32-197.el6.x86_64
qemu-kvm-0.12.1.2-2.192.el6.x86_64
libvirt-0.9.4-12.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Make 2 floppy disk image file

# dd if=/dev/zero of=/var/lib/libvirt/images/fd1.img count=1024 bs=1024

# mkfs.ext3 /var/lib/libvirt/images/fd1.img

# dd if=/dev/zero of=/var/lib/libvirt/images/fd1.img count=1024 bs=1024

# mkfs.ext3 /var/lib/libvirt/images/fd2.img

2. Define a domain with floppy device connected with in config xml file

    <disk type='file' device='floppy'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/fd1.img'/>
      <target dev='fda' bus='fdc'/>
      <readonly/>
    </disk>

3. Start the domain

4. Prepare a xml as flollowing:

# cat floppy.xml
    <disk type='file' device='floppy'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/fd2.img'/>
      <target dev='fda' bus='fdc'/>
      <readonly/>
    </disk>

5. Try to update the media int floppy device

# virsh update-device rhel6 floppy.xml
  
Actual results:
error: Failed to update device from floppy.xml
error: internal error unable to execute QEMU command 'change': Could not open '/var/lib/libvirt/images/fd2.img'

Expected results:
success with no error

Additional info: