On 10/22/2010 08:45 PM, Michael Roth wrote:
This set of patches is meant to be applied on top of the Virtproxy v1 patchset.
OVERVIEW:
There are a wide range of use cases motivating the need for a guest agent of
some sort to extend the functionality/usability/control offered by QEMU.
Some examples include graceful guest shutdown/reboot and notifications thereof,
copy/paste syncing between host/guest, guest statistics gathering, file access,
etc.
Ideally these would all be served by a single, easilly extensible agent that
can be deployed in a wide range of guests.
Virtagent is an XMLRPC server integrated into the Virtproxy guest daemon and
aimed at providing this type of functionality.
This code is very rough, and I'll to document most of the bugs/shortcomings
we're aware of in this version of the patchset.
The main goal of this RFC to get feedback on the types of core functionality we
would need in an agent of this sort, as well as feedback on the general
approach/architecture implemented here.
Any feedback is greatly appreciated however.
To start off this discussion, there have been some recent posts about how much
an agent of this sort overlaps with the goals of the Matahari project
(https://fedorahosted.org/matahari/).
While both of these approaches are at least *feasible*, our use cases require
the ability to deploy to guests which may not support virtio-serial, which
currently rules Matahari out.
This support could be added however: the virtproxy layer used by this agent
actually lends itself to extending such support to other agents/services, or a
more direct approach could be taken in adding support for isa-serial.
The question that remains however is one of scope.
This agent is intended purely as a means to extend qemu's abilities to perform
hypervisor-specific work,
"shutdown/reboot", "statistics", "file gathering"... none of those sound
very "hypervisor-specific" to me ;-)
whereas Matahari aims to extend general system management capabilities to
guests (please correct me if I'm oversimplifying).
As I replied elsewhere, Matahari is both an architecture and a
collection of independent but commonly useful agents.
So while there will be a bunch of other agents doing a bunch of things
you don't care about, you don't have to care that they exist either :-)
A hypothetical QEMU agent would be a independent entity, with both the
daemon and source code completely isolated from any other agents.
It doesn't even need to live in the Matahari project.
Virtagent cannot meet Matahari's goals, whereas Matahari technically can meet
Virtagent's.
My contention however is that the qemu-specific scope/API and shared code base
with a more closely integrated agent will provide a more expedient route to
functional improvements to qemu,
See above. Would leveraging the Matahari architecture but keeping the
agent in the QEMU project address this concern?
while still allowing for the additional functionality/management capabilities
provided by something like Matahari.
DESIGN:
There are actually 2 RPC servers:
1) a server in the guest integrated into the Virtproxy guest daemon which
handles RPC requests from QEMU
Question: Is the scope here purely between a host and its guest? Or is
it intended that one could access the guest daemon from other hosts/guests?
2) a server in the host (integrated into the Virtproxy host daemon, which we
plan to integrate directly into qemu) to handle RPC requests sent by the guest
agent (mainly for handling asynchronous events reported by the agent).
At the Virtagent level, communication is done via standard RPCs (HTTP/TCP
between host and guest). Virtproxy transparently handles transport over a
network or isa/virtio serial channel, allowing the agent to be deployed on
older guests which may not support virtio-serial.
