libvirt users - Nov 2021 - Questions on device-added and device-removed events

Hi developers,
When the guest OS is booting, the event for live attachment could be caught
by libvirt, while the event for live detachment could not.
Version:
libvirt-7.9
qemu-kvm-6.1

Steps:
Terminal 1:
?  ~ virsh event --loop --all

Terminal 2:
?  ~ virsh start avocado-vt-vm1; qemu-img create /tmp/vdb 10M; virsh
attach-disk avocado-vt-vm1 /tmp/vdb vdb; virsh detach-disk avocado-vt-vm1
vdb

The outputs from terminal 1:
event 'agent-lifecycle' for domain 'avocado-vt-vm1': state:
'disconnected'
reason: 'domain started'
event 'lifecycle' for domain 'avocado-vt-vm1': Resumed Unpaused
event 'lifecycle' for domain 'avocado-vt-vm1': Started Booted
event 'device-added' for domain 'avocado-vt-vm1': virtio-disk1
event 'agent-lifecycle' for domain 'avocado-vt-vm1': state:
'connected'
reason: 'channel event'

As you can see, the device live attachment and the device detachment are
both executed when the guest OS is booting, but there is only the event
'device-added' is recorded.
So my questions are:
1. Is it the expected results for the results above?
2. If so, what is the internal difference between 'device-added' and
'device-removed'?
3. I notice there is the DEVICE_DELETED event in qmp? Any relation between
the 'device-removed' of libvirt and the DEVICE_DELETED of qmp?
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On 11/18/21 07:37, Han Han wrote:
> Hi developers,
> When the guest OS is booting, the event for live attachment could be
> caught by libvirt, while the event for live detachment could not.
> Version:
> libvirt-7.9
> qemu-kvm-6.1
> 
> Steps:
> Terminal 1:
> ? ?~ virsh event --loop --all
> 
> Terminal 2:
> ? ?~ virsh start avocado-vt-vm1; qemu-img create /tmp/vdb 10M; virsh
> attach-disk avocado-vt-vm1 /tmp/vdb vdb; virsh detach-disk
> avocado-vt-vm1 vdb
> 
> The outputs from terminal 1:
> event 'agent-lifecycle' for domain 'avocado-vt-vm1': state:
> 'disconnected' reason: 'domain started'? ? ??
> event 'lifecycle' for domain 'avocado-vt-vm1': Resumed
Unpaused
> event 'lifecycle' for domain 'avocado-vt-vm1': Started
Booted
> event 'device-added' for domain 'avocado-vt-vm1':
virtio-disk1
> event 'agent-lifecycle' for domain 'avocado-vt-vm1': state:
'connected'
> reason: 'channel event'
> 
> As you can see, the device live attachment and the device detachment are
> both executed when the guest OS is booting, but there is only the event
> 'device-added' is recorded.
> So my questions are:
> 1. Is it the expected results for the results above?
> 2. If so, what is the internal difference between 'device-added'
and
> 'device-removed'?
> 3. I notice there is the DEVICE_DELETED event in qmp? Any relation
> between the 'device-removed' of libvirt and the DEVICE_DELETED of
qmp?
Detaching a device requires the guest cooperation, while in contrast the
device attach does not. So I'm guessing that your guest isn't in a state
where it can satisfy the detach request.

The DEVICE_REMOVED event is emitted whenever DEVICE_DELETED event
appears on the monitor (may be delayed for a couple of microseconds,
because libvirt needs to update its internal state first).

Hope this helps.

Michal