On Tue, Dec 06, 2011 at 08:34:06AM -0600, Michael Roth wrote:
The code is still in rough shape, but while we're on the topic of guest agents
I wanted to put out a working example of how exec functionality can be added
to qemu-ga to provide a mechansim for building arbitrarilly high-level
interfaces.
The hope is that by allowing qemu-ga to execute commands in the guest, paired
with file read/write access, we can instrument a guest "on the fly" to support
any type of hyperviser functionality, and do so without dramatically enlarging
the role qemu-ga plays as a small, QEMU-specific agent that is tightly
integrated with QEMU/QMP/libvirt.
These patches add the following interfaces:
guest-file-open-pipe
guest-exec
guest-exec-status
The guest-file-open-pipe interface is analagous to the existing guest-file-open
interface (it might be best to roll it into it actually): it returns a handle
that can be handled via the existing guest-file-{read,write,flush,close}
interface. Internally it creates a FIFO pair that we can use to associate
handles to the stdin/stdout/stderr of a guest-exec spawned process. We can also
also use them to redirect output into other processes, giving us the basic
tools to build a basic shell (or a full-blown one if we add TTY support) using
a single qemu-ga.
Theoretically we can even deploy other agents, including session-level agents,
and communicate with them via these same handles. Thus, ovirt could deploy and
run an agent via qemu-ga, Spice could deploy vdagent, etc. Since the interface
is somewhat tedious, I'm working on a wrapper script to try out some of
these scenarios, but a basic use case using the raw QMP interface is included
below.
Any thoughts/comments on this approach are appreciated.
EXAMPLE USAGE (execute `top -b -n1`):
{'execute': 'guest-file-open-pipe'}
{'return': 6}
{'execute': 'guest-exec', \
'arguments': {'detach': True, \
'handle_stdout': 6, \
'params': [{'param': '-b'}, \
{'param': '-n1'}], \
'path': 'top'}}
This feels like a rather verbose way of specifying
the ARGV. Why not just allow
{'execute': 'guest-exec', \
'arguments': {'detach': True, \
'handle_stdout': 6, \
'params': ['-b', '-n1'], \
'path': 'top'}}
Or even
{'execute': 'guest-exec', \
'arguments': {'detach': True, \
'handle_stdout': 6, \
'argv': ['top', '-b', '-n1']}} \
and just use the first element of argv as the binary to
execute. Also you might need to set env variables for
some tools, so we'd want
{'execute': 'guest-exec', \
'arguments': {'detach': True, \
'handle_stdout': 6, \
'argv': ['top', '-b', '-n1'], \
'env' : ['TMPDIR=/wibble']}}
and perhaps also you might want to run as a non-root
user, so allow a username/groupname ?