# From host, check the running guest XML for QEMU guest agent XML snippet:
#
[host]$ virsh dumpxml f22vm | grep unix -A5
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/f22vm.org.qemu.guest_agent.0'/>
      <target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
      <alias name='channel0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>


# Check the status of QEMU Guest Agent in the guest
[guest]$ systemctl status qemu-guest-agentQEMU
● qemu-guest-agent.service - QEMU Guest Agent
   Loaded: loaded (/usr/lib/systemd/system/qemu-guest-agent.service; static; vendor preset: enabled)
   Active: active (running) since Sat 2015-09-26 09:56:54 EDT; 2 months 25 days ago
 Main PID: 489 (qemu-ga)
   CGroup: /system.slice/qemu-guest-agent.service
           └─489 /usr/bin/qemu-ga

Sep 26 09:56:54 localhost.localdomain systemd[1]: Started QEMU Guest Agent.
Sep 26 09:56:54 localhost.localdomain systemd[1]: Starting QEMU Guest Agent...
Dec 21 09:38:36 localhost.localdomain systemd[1]: Started QEMU Guest Agent.


# Take a snapshot of the guest, supplying the '--quisce' which
# *requires* QEMU Guest Agent to be running
[host] $ virsh snapshot-create-as --domain f22vm snap1 \
            --diskspec vda,file=/export/vmimages/snap1.qcow2 \
            --disk-only --atomic --quiesce
Domain snapshot snap1 created


Additional info
---------------

Snapshot info:

[host]$ virsh snapshot-list f22vm
 Name                 Creation Time             State
------------------------------------------------------------
 snap1                2015-12-21 09:43:36 -0500 disk-snapshot

[host]$ virsh domblklist f22vm
Target     Source
------------------------------------------------
vda        /export/vmimages/snap1.qcow2