Re: [Qemu-devel] Re: virtio-serial: An interface for host-guest communication

[Anthony Liguori <anthony@codemonkey.ws>]

Jamie Lokier wrote:
> Anthony Liguori wrote:
>   
>> Richard W.M. Jones wrote:
>> Have you considered using a usb serial device?  Something attractive 
>> about it is that a productid/vendorid can be specified which means that 
>> you can use that as a method of enumerating devices.
>>
>> Hot add/remove is supported automagically.
>>     
>
> The same applies to PCI: productid/vendorid (and subids);
> PCI hotplug is possible though not as native as USB.
>   

What's nice about USB is that HID specifies quite a few functional 
generic devices that can be extended to increase functionality.  This 
means you can implement a more sophisticated usb device that satisfies 
the serial interface, provide a special more featureful driver for 
Linux, and just use normal serial for Windows.

The downside is that USB emulation stinks.

> Here's another idea: Many devices these days have a serial number or
> id string.  E.g. USB storage, ATA drives, media cards, etc.  Linux
> these days creates alias device nodes which include the id string in
> the device name.  E.g. /dev/disks/by-id/ata-FUJITSU_MHV2100BH_NWAQT662615H
>
> So in addition to (or instead of) /dev/vmch0, /dev/vmch1 etc.,
> Linux guests could easily generate:
>
>     /dev/vmchannel/by-role/clipboard-0
>     /dev/vmchannel/by-role/gueststats-0
>     /dev/vmchannel/by-role/vmmanager-0
>
> It's not necessary to do this at the beginning.  All that is needed is
> to provide enough id information that will appear in /sys/..., so that
> that a udev policy for naming devices can be created at some later date.
>   

Well my thinking is that the "clipboard" device actually becomes a USB 
serial device.  It's easy to enumerate and detect via the existing Linux 
infrastructure.  Plus usb drivers can be implemented in userspace which 
is a nice plus (cross platform too via libusb).

Regards,

Anthony Liguori

> -- Jamie
>