[Libguestfs] [v2v PATCH v2 1/4] output/create_libvirt_xml: wire up the QEMU guest agent

[Richard W.M. Jones]

On Mon, Jun 13, 2022 at 07:01:32PM +0200, Laszlo Ersek wrote:
> The intent (even before RHBZ#2028764) has been to install the QEMU guest
> agent in the converted domain unconditionally. Therefore, in order for the
> GA to be actually accessible from the host side, augment the libvirt
> output module with a "guest agent connection" also unconditionally.
> 
> For starters, the domain needs a virtio-serial device. Then there must be
> a port on the device that (in the guest) the GA identifies by name, and
> that (on the host) is exposed as a listening socket (usually in the unix
> address family). The adress of that port (usually a pathname, i.e., for a
> unix domain socket) is then passed to whatever host-side application wants
> to talk to the GA.
> 
> The minimal domain XML fragment for that ("minimal" for our purposes) is
> 
>   <controller type='virtio-serial' model='virtio'>
>   <channel type='unix'>
>     <target type='virtio' name='org.qemu.guest_agent.0'/>
>   </channel>
> 
> The "controller" element is needed because "controller/@model" is where we
> regulate "virtio" vs. "virtio-transitional".
> 
> Everything else is filled in by libvirt. Notably, libvirt (a) creates and
> binds the unix domain socket itself (usually
> "/var/lib/libvirt/qemu/channel/target/DOMAIN/org.qemu.guest_agent.0"), (b)
> passes the file descriptor to QEMU, and (c) figures out the socket
> pathname for commands such as
> 
>   virsh domfsinfo DOMAIN
>   virsh domhostname DOMAIN --source agent
>   virsh domifaddr DOMAIN --source agent
>   virsh guestinfo DOMAIN
> 
> For QEMU, the corresponding options would be
> 
>   -chardev socket,id=agent,server=on,wait=off,path=/tmp/DOMAIN-agent \
>   -device virtio-serial-pci,id=vioserial \
>   -device virtserialport,bus=vioserial.0,nr=1,chardev=agent,name=org.qemu.guest_agent.0 \
> 
> Note the "path=/tmp/DOMAIN-agent" property of "-chardev"; virt-v2v would
> have to generate that (in place of the "fd=nnnn" property that libvirt
> passes to QEMU).
> 
> Omit extending the QEMU output module for now, as the QGA protocol is
> based on JSON, and one needs "virsh" or "virt-manager" (or another
> management application interface) anyway, for efficiently exchanging
> messages with QGA. I don't know of end-user tools that directly connect to
> "/tmp/DOMAIN-agent".
> 
> Don't modify the RHV and OpenStack outputs either; both of these
> management products likely configure the virtio-serial device
> automatically, for the agent access.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2028764
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> Notes:
>     v2:
>     - no change
> 
>  output/create_libvirt_xml.ml | 11 +++++++++++
>  tests/test-v2v-i-ova.xml     |  4 ++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/output/create_libvirt_xml.ml b/output/create_libvirt_xml.ml
> index 68d0a90918f3..531a4f75bf3e 100644
> --- a/output/create_libvirt_xml.ml
> +++ b/output/create_libvirt_xml.ml
> @@ -524,6 +524,17 @@ let create_libvirt_xml ?pool source inspect
>      e "console" ["type", "pty"] [];
>    ];
>  
> +  (* Given that we install the QEMU Guest Agent for both Linux and Windows
> +   * guests unconditionally, create the virtio-serial device that's needed for
> +   * communication between the host and the agent.
> +   *)
> +  List.push_back_list devices [
> +    e "controller" ["type", "virtio-serial"; "model", virtio_model] [];
> +    e "channel" ["type", "unix"] [
> +      e "target" ["type", "virtio"; "name", "org.qemu.guest_agent.0"] []
> +    ]
> +  ];
> +
>    List.push_back_list body [
>      e "devices" [] !devices;
>    ];
> diff --git a/tests/test-v2v-i-ova.xml b/tests/test-v2v-i-ova.xml
> index 6b8cda62f051..da1db473e53c 100644
> --- a/tests/test-v2v-i-ova.xml
> +++ b/tests/test-v2v-i-ova.xml
> @@ -49,5 +49,9 @@
>      <input type='tablet' bus='usb'/>
>      <input type='mouse' bus='ps2'/>
>      <console type='pty'/>
> +    <controller type='virtio-serial' model='virtio'/>
> +    <channel type='unix'>
> +      <target type='virtio' name='org.qemu.guest_agent.0'/>
> +    </channel>
>    </devices>
>  </domain>

Reviewed-by: Richard W.M. Jones <rjones at redhat.com>
Tested-by: Richard W.M. Jones <rjones at redhat.com>

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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