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From 11.2:
> However, there are the following limitations with regards to isa-serial/virtio-serial transport:
>
> The qemu-guest-agent cannot detect whether or not a client has connected to the channel.
As far as I can tell, this sentence should remain - the guest does not know if someone in the host is listening to the channel.
> There is no way for a client to detect whether or not qemu-guest-agent has disconnected or reconnected to the back-end.
This sentence can be dropped. Libvirt can now tell if qemu-guest-agent has the channel opened, and recognizes when the guest drops and then reconnects over a qemu-guest-agent restart. Libvirt is able to intelligently quit attempting guest agent commands if the guest agent is not connected.
> If the virtio-serial device resets and qemu-guest-agent has not connected to the channel (generally caused by a reboot or hotplug), data from the client will be dropped.
This is still true. But not very consequential - since libvirt knows when the agent is connected, it is not going to send data before that point. So you can drop the sentence.
> If qemu-guest-agent has connected to the channel following a virtio-serial device reset, data from the client will be queued (and eventually throttled if available buffers are exhausted), regardless of whether or not qemu-guest-agent is still running or connected.
Again, still true but not very consequential, so you can drop the sentence.