[libvirt] virsh [attach-detach]-device question

[Scott Sullivan]

On 08/06/2013 08:54 AM, Scott Sullivan wrote:
> I have noticed a behavior I am hoping someone can help me understand. 
> Consider the following scenario:
>
> 1.) Start a test dummy qemu-kvm instance with no OS via virsh named 
> "no_os".
>
> 2.) Attach a device to it;
> [root at host ~]# virsh attach-device no_os /root/hotplug_device_b.xml
> Device attached successfully
>
> [root at host ~]#
>
> 3.) Now detach the same device;
> [root at host ~]# virsh detach-device no_os /root/hotplug_device_b.xml
> Device detached successfully
>
> [root at host ~]#
>
> 4.) Now re-attach the same device;
> [root at host ~]# virsh attach-device no_os /root/hotplug_device_b.xml
> error: Failed to attach device from /root/hotplug_device_b.xml
> error: internal error unable to execute QEMU command 'device_add': 
> Duplicate ID 'virtio-disk1' for device
>
> [root at host ~]#
>
> Is this expected behavior? If so, why does my detach-device call in 
> step 3 appear to not free the device, leading to the duplicate ID 
> error in step 4?
>
> Libvirt XML's used:
>
> /root/hotplug_device_b.xml:
>
> <disk type='block' device='disk'>
> <driver name='qemu' cache='none'/>
> <source dev="/dev/syseng/hotplug_test_b"/>
> <target dev="vdb" bus="virtio"/>
> </disk>
>
> I started the "no_os" instance with this:
>
> <domain type="kvm">
> <name>no_os</name>
> <uuid>E605BE96-6BC9-11E2-976C-EDA8DB8AEF42</uuid>
> <memory>524288</memory>
> <currentMemory>524288</currentMemory>
> <vcpu>1</vcpu>
> <os>
> <type arch="x86_64" machine="pc-1.1">hvm</type>
> <boot dev="hd"/>
> </os>
> <features>
> <acpi/>
> <apic/>
> <pae/>
> </features>
> <clock offset="utc"/>
> <on_poweroff>destroy</on_poweroff>
> <on_reboot>restart</on_reboot>
> <on_crash>restart</on_crash>
> <devices>
> <emulator>/opt/kvm-stack-1/libexec/qemu-kvm-wrapper</emulator>
> <disk type="block" device="disk">
> <driver name="qemu" cache="none"/>
> <source dev="/dev/LVM/no_os"/>
> <target dev="vda" bus="virtio"/>
> </disk>
> <disk type="file" device="cdrom">
> <target dev="hdc" bus="ide"/>
> <readonly/>
> </disk>
>
> <serial type="pty">
> <target port="0"/>
> </serial>
> <console type="pty">
> <target port="0"/>
> </console>
> <input type="mouse" bus="ps2"/>
> <graphics type="vnc" port="-1" autoport="yes" keymap="en-us"/>
> <interface type="bridge">
> <mac address="52:54:00:87:14:3d"/>
> <source bridge="virbr0"/>
> <target dev="no_os_0"/>
> <model type="virtio"/>
> </interface></devices>
> </domain>
>
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After some digging, it looks like what i'm looking for is covered by 
this bugzilla:

https://bugzilla.redhat.com/show_bug.cgi?id=970761

So we would want to

1. device_del

2. Wait for DEVICE_DELETED

3. if timeout, drive_del

Might make sense to offer a choice in the API between "fail" and 
"destroy the block device" if guest doesn't cooperate.