spapr-vty is not a serial device, although it works somewhat like one.  So attempting to use /dev/ttyS1 for the qemu-ga certainly won't work.  You will need /dev/hvc1 instead.

(In reply to David Gibson from comment #2)
> spapr-vty is not a serial device, although it works somewhat like one.  So
> attempting to use /dev/ttyS1 for the qemu-ga certainly won't work.  You will
> need /dev/hvc1 instead.

Yeah, thanks for the remind, /dev/hvc0-7 should be the device inside guest for spapr-vty.

But there's still issue with spapr-vty:

#qemu-ga -m 
First, there's no "spapr-vty" method currently. So I just tried "#qemu-ga -m isa-serial -p /dev/hvc1" (obviously this is not correct, just an experiment here) and "#qemu-ga -m unix-listen -p /dev/hvc1", neither of them works:

(1) Inside guest: qemu-ga -m unix-listen -p /dev/hvc1
   On host: # nc -U /tmp/serial2

 {"execute":"guest-sync", "arguments":{"id":1234}}

 ======> No response

(2) Inside guest: qemu-ga -m isa-serial -p /dev/hvc1
   On host: # nc -U /tmp/serial2

 {"execute":"guest-info"}
{"error": {"class": "GenericError", "desc": "Invalid JSON syntax"}}
{"error": {"class": "GenericError", "desc": "JSON parse error, invalid keyword `nfo'"}}

So, spapr-vty is not a serial port but it should operate as a character channel just like a serial port.  So using the same mode as for a virtserialport should the the right choice for qemu-ga.

(In reply to David Gibson from comment #4)
> So, spapr-vty is not a serial port but it should operate as a character
> channel just like a serial port.  So using the same mode as for a
> virtserialport should the the right choice for qemu-ga.

Maybe the trial in comment 3 had some configuration issue or something else.  Now the guest agent works for both "-m isa-seiral" and "-m virtio-serial".


(1) In guest:

# qemu-ga -m virtio-serial -p /dev/hvc1

On host:

# nc -U /tmp/serial2

 {"execute":"guest-sync", "arguments":{"id":1234}}
 {"execute":"guest-sync", "arguments":{"id":1234}} (==> this line is returned automatically, maybe a bug? )
{"return": 1234}


(2) In guest:

# qemu-ga -m isa-serial -p /dev/hvc1

On host: 

 {"execute":"guest-sync", "arguments":{"id":1234}}
{"return": 1234}

Now the guest agent work, however "-m isa-serial" and "-m virtio-serial" obviously are not suitable although it's trivial issue, could we fix in qemu-guest-agent? 

Thanks,
Qunfang

Hi, David

Can something be fixed in guest agent according to comment 5?

So, I guess we could add spapr-vty as an alias to one of the other serial options in qemu-ga.

It's pretty low priority, since AFAIK in every current use case we use virtio-serial for qemu-ga, instead of spapr-vty.

I've now looked at the guest agent code a bit more closely.

Any machine with spapr-vty should also be capable of supporting virtio-serial, so I don't see that there's any real need for qemu-ga to support operating over spapr-vty, although it will work.

So, there seems even less need to have an "spapr-vty" option.