[libvirt] About 'virsh update-device' for floppy and cdrom

[liyang]

Hi experts:
When I did some test, I was puzzled by one thing: When I use "virsh 
update-device" to update
floppy device, always got an error message, "error: internal error 
unable to execute QEMU command
'change': Could not open'***file':Permission denied".But when I execute 
command "setenforce 0"
befroe "udpate-device", floppy device can be updated.

Steps like this:
---------------------------------------------------------------Start
# virsh start virt-tests-vm1
Domain virt-tests-vm1 started

# cat 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml
<disk type='file' device='floppy'>
<driver name='qemu' type='raw'/>
<source 
file='/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso'/>
<target dev='fda'/>
<readonly/>
</disk>
# ll 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso
-rw-r--r--. 1 qemu qemu 1404928 Sep 20 10:48 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso
# virsh update-device virt-tests-vm1 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml 
--force
error: Failed to update device from 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml
error: internal error unable to execute QEMU command 'change': Could not 
open 
'/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso': 
Permission denied

# cat /selinux/enforce
1
# setenforce 0
# virsh update-device virt-tests-vm1 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml 
--force
Device updated successfully
---------------------------------------------------------------End

But with same command, about cdrom device it worked though 
"/selinux/enforce" is 1.
Steps like this:
---------------------------------------------------------------Start
# virsh start virt-tests-vm1
Domain virt-tests-vm1 started

# cat 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml

<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<source 
file='/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso'/>
<target dev='hdc'/>
<readonly/>
</disk>
# ll 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso
-rw-r--r--. 1 qemu qemu 1404928 Sep 20 10:58 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/change_media_old.iso
# cat /selinux/enforce
1
# virsh update-device virt-tests-vm1 
/add_storage/liyang/github-autotest_new/client/tests/virt/tmp/tmp/update_iso.xml 
--force
Device updated successfully
---------------------------------------------------------------End

So I want to know why it's different between 'floppy' and 'cdrom', and 
what's the difference?
Also why floppy needs 'permissive' mode but cdrom doesn't?

Wish your help!

-- 
Regards,
--------------------------------------------------
Li Yang
TEL：+86+25-86630566-8529
EMail：liyang.fnst at cn.fujitsu.com
--------------------------------------------------