[Spice-devel] Implementing channel between module at spice client and guest OS

[Marc-André Lureau]

Hi

On Mon, Nov 18, 2013 at 7:22 PM, Alon Bar-Lev <alonbl at redhat.com> wrote:
> Hello,
>
> I am trying to figure out how to implement a channel between guest OS process and component at client machine. Reading the documentation I found and the vd_agent code which is somewhat similar but I could not find complete solution.
>
> Here is what I imagined....
>
> I define a new serial interface on qemu:
>
> -device virtio-serial-pci
> -device virtserialport,chardev=myappl,name=my.application.0
> -chardev spicevmc,id=myappl,name=myappl
>
> This will enable a process within guest os to access /dev/virtio-ports/my.application.0


If you use a spicevmc name, you'll have to modify Spice server
(spice_server_char_device_add_interface), and implement the channel
handling in client. This can be tedious and doesn't allow "private"
extensions.

But recently, we added the spice "port", which is just like spicevmc,
except that you can have "private channels" without modifiying server
etc.

It hasn't been widely used (even less when connected to a virtio
port), but you can try using it:

-chardev spiceport,id=spiceportfoobar,name=com.foobar -device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=spiceportfoobar,id=channel1,name=com.foobar

> At client side I would like to implement a component that interact with this myappl port, I could not find a way to load shared library or similar dynamic module into client in spicy usage.
>

At client side, you can follow spicy.c example. In channel_new(), you
want to connect to the port channel signals. When
"notify::port-opened", you can decide to handle that channel  based on
its "port-name".

> If dynamic loading of modules is possible, is there any example of how to do so?
>
> If dynamic loading of modules is impossible, is there a plan to allow it?

There is currently no registry of channel or port handlers to be
loaded dynamically. There is currently no plan to add it, but that
could be added later.

> Assuming there is the option to load a module.
>
> I could not find in vdi spec[1] description of the vdi_port interface and what should I do in order to communicate with the guest.
>
> Provided this is possible somehow, as it is working for vd_agent... and provided external modules can be loaded.
>
> I can guess that each 'name' in the above example myapp can be connected by different implementation, is that right?
>
> Assuming we have channel between module running on client machine and the agent running on guest machine using virtual serial, is there support for transferring RS232 controls? Such as DTR/DSR to detect if the device is opened at guest side and if device is opened at client side? And detect disconnection?


You can also redirect a serial device from qemu:

-chardev spiceport,id=spiceportfoobar,name=org.spice.spicy -serial
chardev:spiceportfoobar

(with kernel argument "console=tty0 console=ttyS0,115200n8")


> Another nice option I thought is to allow forking process at client side with usock as stdin/stdout that redirected into specific spicevmc device, this will ease the work of implementing such solutions, as the author of the forked process may not have any spice knowledge at all, while be able to participate within the solution.

That's a possibility, patches welcome.

>
> Regards,
> Alon Bar-Lev.
>
> [1] http://www.spice-space.org/docs/vd_interfaces.pdf
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-- 
Marc-André Lureau