[Qemu-devel] A new direction for vmchannel?

[Anthony Liguori]

The userspace configuration aspects of the current implementation of 
vmchannel are pretty annoying.  Moreover, we would like to make use of 
something like vmchannel in a kernel driver and I fear that it's going 
to be difficult to do that.

So here's an alternative proposal.

Around 2.6.27ish, Eric and I added 9p over virtio support to v9fs.  This 
is all upstream.  We backported the v9fs modules all the way back to 
2.6.18.  I have a 9p client and server library and patches available for 
QEMU.  We were using this for a file system pass through but we could 
also use it as a synthetic file system in the guest (like sysfs).

The guest would just have to mount a directory in a well known location, 
and then you could get vmchannel like semantics by just opening a file 
read/write.  Better yet though would be if we actually exposed vmchannel 
as 9p so that management applications could implement sysfs-like 
hierarchies.

I think there could be a great deal of utility in something like.  For 
portability to Windows (if an app cared), it would have to access the 
mount point through a library of some sort.  We would need a Windows 
virtio-9p driver that exposed the 9p session down to userspace.  We 
could then use our 9p client library in the portability library for Windows.

Virtually all of the code is available for this today, the kernel bits 
are already upstream, there's a reasonable story for Windows, and 
there's very little that the guest can do to get in the way of things.

The only thing that could potentially be an issue is SELinux.  I assume 
you'd have to do an SELinux policy for the guest application anyway 
though so it shouldn't be a problem.

Thoughts?

Regards,

Anthony Liguori