# Enable tracing
In virsh

     qemu-monitor-command <vm> --hmp trace-event usb_xhci_* on
     qemu-monitor-command <vm> --hmp info trace-events

output goes to /var/log/libvirt/qemu/<vm>.log by default

# 9pfs
* Libvirt XML

        <filesystem type='mount' accessmode='mapped'>
            <source dir='/cache/ltstest'/>
            <target dir='ltstest'/>
        </filesystem>

*mapped* is important. It uses extended attributes so the filesystem that
needs to be mounted with *user_xattr* on the host filesystem and the folder
needs to be writeable by qemu:

        mount -o remount,user_xattr /cache/ltstest
        chown libvirt-qemu /cache/ltstest

The Guests fstab then uses:

    ltstest /ltstest 9p   trans=virtio,version=9p2000.L,rw 0 0

After mounting you can write from the guest to the hosts fileystem:

    mount /ltstest
    cd /ltstest && touch a

results on the host as extended attributes

     # attr -l a
     Attribute "virtfs.uid" has a 4 byte value for a
     Attribute "virtfs.gid" has a 4 byte value for a
     Attribute "virtfs.mode" has a 4 byte value for a

For details on 9pfs see http://man.cat-v.org/plan_9/5/intro

# Hot (un)plug Devices #

## PCI devices ##

    http://www.linux-kvm.org/page/Hotadd_pci_devices

## UARTs ##

    http://nairobi-embedded.org/qemu_character_devices.html

## Sound ##
Devices are not hotpluggable via libvirt
([#1417464](https://bugzilla.redhat.com/show_bug.cgi?id=1417464)) but
via QMP monitor:

        qemu-monitor-command <vm> '{ "execute": "device_add",  "arguments": { "driver": "ES1370", "id": "snd1" }}'
		qemu-monitor-command <vm> '{ "execute": "device_del",  "arguments": { "id": "snd1" }}

        qemu-monitor-command <vm> '{ "execute": "device_add",  "arguments": { "driver": "AC97", "id": "snd2" }}'
		qemu-monitor-command <vm> '{ "execute": "device_del",  "arguments": { "id": "snd2" }}

[More details on QMP commands](https://git.qemu.org/?p=qemu.git;a=blob;f=qapi-schema.json)

# Misc #

* List all devices:

        qemu-system-x86_64 -device ?

* Enabling the monitor on raw qemu

        $ qemu-system-i386 -qmp tcp:localhost:4444,server,nowait
		$ telnet localhost 4444
		{ "execute": "qmp_capabilities" }
		{"execute": "commands"}