Verification done on focal-proposed, following comments 23, 24, 25, 26.

Including in this comment a few key snippets from each test/comment.

---
Environment
---

LXD virtual machine

 lxc launch --vm ubuntu:focal lp2059272-focal
 lxc exec lp2059272-focal -- su - ubuntu

Enable proposed & debug symbols

	cat <<EOF | sudo tee /etc/apt/sources.list.d/proposed.list
	deb http://archive.ubuntu.com/ubuntu focal-proposed main universe
	deb http://ddebs.ubuntu.com focal-proposed main universe
	EOF

	cat <<EOF | sudo tee /etc/apt/preferences.d/proposed
	Package: *
	Pin: release a=focal-proposed
	Pin-Priority: 400
	EOF

	sudo apt install --yes --no-install-recommends gdb qemu-system-x86 ubuntu-dbgsym-keyring
	sudo apt update
	sudo apt install --yes --no-install-recommends -t focal-proposed libvirt{0,-daemon{,-driver-qemu,-system}}{,-dbgsym} libvirt-clients

	$ apt-cache policy libvirt-daemon-driver-qemu
	libvirt-daemon-driver-qemu:
	  Installed: 6.0.0-0ubuntu8.20
	  Candidate: 6.0.0-0ubuntu8.20
	  Version table:
	 *** 6.0.0-0ubuntu8.20 400
		400 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 Packages
		100 /var/lib/dpkg/status
	     6.0.0-0ubuntu8.19 500
		500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
		500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
	     6.0.0-0ubuntu8 500
		500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

	newgrp libvirt # or logout/login

Libvirtd debug logging

	cat <<-EOF | sudo tee -a /etc/libvirt/libvirtd.conf
	log_filters="1:qemu 1:libvirt"
	log_outputs="3:syslog:libvirtd 1:file:/var/log/libvirt/libvirtd-debug.log"
	EOF

---
Steps with test packages on Focal (normal restarts)
---

	<...>
	for SLEEP in $(seq 0.1 0.1 2.0); do
	<...>
	
All VMs are still managed by libvirt:

	$ virsh list
	 Id   Name         State
	----------------------------
	 1    test-vm-1    running
	 2    test-vm-2    running
	 3    test-vm-3    running
	 4    test-vm-4    running
	 5    test-vm-5    running
	 6    test-vm-6    running
	 7    test-vm-7    running
	 8    test-vm-8    running
	 9    test-vm-9    running
	 10   test-vm-10   running


---
Steps with test packages on Focal (shutdown-on-init)
---

Scenario 1) Shutdown wins race against XML update (ie, shutdown happens first)

<...>

Now, let the qemuProcessReconnect thread continue, it will not update the XML file,
because 'quit' is set (ie, shutdown in progress)

	(gdb) t 20
	(gdb) p ((virNetDaemonPtr)anyobj)->quit
	$2 = true

	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10189 Apr 24 12:02 /run/libvirt/qemu/test-vm.xml

	(gdb) c &

	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10189 Apr 24 12:02 /run/libvirt/qemu/test-vm.xml

	<...>
	
	$ sudo grep 'Leaving the update of .* domain status XML' /var/log/libvirt/libvirtd-debug.log
	2024-04-24 12:08:40.054+0000: 3770: info : qemuProcessReconnect:8157 : Leaving the update of 'test-vm' domain status XML for the next initialization (shutdown detected on this initialization).

	<...>
	
	$ sudo grep -e '<domstatus' -e '<domain' -e 'monitor path' /run/libvirt/qemu/test-vm.xml
	<domstatus state='running' reason='booted' pid='3726'>
	  <monitor path='/var/lib/libvirt/qemu/domain-1-test-vm/monitor.sock' type='unix'/>
	  <domain type='qemu' id='1'>

Scenario 2) Shutdown loses race against XML update (ie, update happens first)

<...>

Instead, let the qemuProcessReconnect thread take the lock, and update the XML file, but not unlock yet

	<...>
	
	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10189 Apr 24 12:02 /run/libvirt/qemu/test-vm.xml

	(gdb) b virObjectUnlock thread 20 if anyobj == $ptr
	(gdb) c
	
	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10189 Apr 24 12:14 /run/libvirt/qemu/test-vm.xml

	<...>

	$ sudo grep -e '<domstatus' -e '<domain' -e 'monitor path' /run/libvirt/qemu/test-vm.xml
	<domstatus state='running' reason='booted' pid='3726'>
	  <monitor path='/var/lib/libvirt/qemu/domain-1-test-vm/monitor.sock' type='unix'/>
	  <domain type='qemu' id='1'>

Scenario 3) Shutdown happens along QEMU monitor calls (ie, calls don't finish)

<...>

	The XML was not updated, as expected:

	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10189 Apr 24 12:14 /run/libvirt/qemu/test-vm.xml

	$ sudo grep -e '<domstatus' -e '<domain' -e 'monitor path' /run/libvirt/qemu/test-vm.xml
	<domstatus state='running' reason='booted' pid='3726'>
	  <monitor path='/var/lib/libvirt/qemu/domain-1-test-vm/monitor.sock' type='unix'/>
	  <domain type='qemu' id='1'>
<...>

Now, the next time libvirtd starts, it correctly parses that XML:

	 $ sudo systemctl start libvirtd.service

	 $ journalctl -b -u libvirtd.service | grep -A1 error
	 $
	 
And libvirt is aware of the domain, and can manage it:

	$ virsh list
	 Id   Name      State
	-------------------------
	 1    test-vm   running

	$ virsh destroy test-vm
	Domain test-vm destroyed

	$ virsh undefine test-vm
	Domain test-vm has been undefined

---
Steps with test packages on Focal (shutdown-on-runtime)
---

<...>
Check the formatter/options again; it is *STILL* referenced, not 0x0 anymore:

	(gdb) t 20
	(gdb) p xmlopt.privateData.format
	$3 = (virDomainXMLPrivateDataFormatFunc) 0x7fd08c3437c0 <qemuDomainObjPrivateXMLFormat>
	(gdb) p/x xmlopt.parent
	$4 = {u = {dummy_align1 = 0x1cafe0026, dummy_align2 = 0x1cafe0026, s = {magic = 0xcafe0026, refs = 0x1}}, klass = 0x7fd080043170}

Let the save function continue, and libvirt finishes shutting down:
<...>
Check the VM status XML *after*:

	$ ls -l /run/libvirt/qemu/test-vm.xml
	-rw------- 1 root root 10251 Apr 24 12:28 /run/libvirt/qemu/test-vm.xml

	$ sudo grep -e '<domstatus' -e '<domain' -e 'monitor path' /run/libvirt/qemu/test-vm.xml
	<domstatus state='running' reason='booted' pid='4055'>
	  <monitor path='/var/lib/libvirt/qemu/domain-1-test-vm/monitor.sock' type='unix'/>
	  <domain type='qemu' id='1'>

Now, the next time libvirtd starts, it correctly parses that XML:

	$ sudo systemctl start libvirtd.service

	$ journalctl -b -u libvirtd.service | grep -A1 error
	$

And libvirt is aware of the domain, and can manage it:

	$ virsh list
	Id Name State
	-------------------------
	1 test-vm running

	$ virsh destroy test-vm
	Domain test-vm destroyed

	$ virsh undefine test-vm
	Domain test-vm has been undefined