Description of problem:
when <shareable/> removed from scsi hostdev xml, related chardev's unpriv_sgio not set back to zero.

Version-Release number of selected component (if applicable):
libvirt-4.5.0-10.virtcov.el7.x86_64
qemu-kvm-rhev-2.12.0-17.el7.x86_64


How reproducible:
100%

---- From John Ferlan ----
> Going back to the problem statement and the dump of the hostdev:
> So, I think this particular issue can be set as notabug; however, there is
> an interesting gotcha that I did find in the code. Because the code returns
> 0 early, if unpriv_sgio was previously set, then someone removes the
> <shareable/> element from the domain, the sysfs value won't get changed.
> 
> ...
>     } else if (dev->type == VIR_DOMAIN_DEVICE_HOSTDEV) {
>         hostdev = dev->data.hostdev;
> 
>         if (!qemuIsSharedHostdev(hostdev))
>             return 0;
> 
>         if (!(hostdev_path = qemuGetHostdevPath(hostdev)))
>             goto cleanup;
> 
>         path = hostdev_path;
>     } else {
> ...
> 
> Note the quiet return 0 if not shared.
> 
> But that's a "different" bug/issue... Present in existing code and fix-able
> in a "future" revision.  It's not that big a deal anyway.
> 
> I did test that I could fix it though... Using the /home/libvirt-rhel
> repository that I built with the /home/libvirt-rhel/amend.patch, you can
> "service libvirtd stop", then "setenforce 0", "/home/libvirt-rhel/run
> /home/libvirt-rhel/src/libvirtd", and then see that when the <shareable/> is
> removed from the domain that a previously set value of 1 is returned to 0.
> And then restore things by quitting the libvirtd, resetting "setenforce
> enforcing", and restarting libvirt "service libvirtd start".
> 
> I've left the system essentially the same way I found it with avocado-vt-vm1
> running *without* the <shareable/> set on the hostdev. You can test that at
> least by adding <shareable/> and restarting the domain that you get what's
> expected.


So the reproduce steps could be as follow:
1. start a vm with following xml (you can prepare a iscsi lun to be used, here is 89:0:0:0)
    <hostdev mode='subsystem' type='scsi' managed='no' sgio='unfiltered'>
      <source>
        <adapter name='scsi_host89'/>
        <address bus='0' target='0' unit='0'/>
      </source>
      <shareable/>
      <alias name='hostdev0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </hostdev>

# virsh start avocado-vt-vm1
Domain avocado-vt-vm1 started

2. check the scsi device's unpriv_sgio value on host
# cat /sys/dev/block/*/device/unpriv_sgio
0
1 <==== here is changed from 0 to 1

3. destroy and edit vm's hostdev xml, remove the <shareable/>
    <hostdev mode='subsystem' type='scsi' managed='no' sgio='unfiltered'>
      <source>
        <adapter name='scsi_host89'/>
        <address bus='0' target='0' unit='0'/>
      </source>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </hostdev>

4. start the vm again
# virsh start avocado-vt-vm1
Domain avocado-vt-vm1 started

5. check the unpriv_sgio value
[root@ibm-x3650m3-08 ~]# cat /sys/dev/block/*/device/unpriv_sgio
0
1 <==== it's still 1, not changed back to 0

Actual result:
as step 5

Expected result:
if remove shareable tag from hostdev, its unpriv_sgio value should be changed back to 0