[Qemu-devel] [PATCH 0/2] [RFC] qemu-ga: add support for guest command execution

[Michael Roth <mdroth@linux.vnet.ibm.com>]

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'}}
{'return': {'exit-code': 0,                  \
            'exited': False,                 \
            'handle_stderr': -1,             \
            'handle_stdin': -1,              \
            'handle_stdout': 6,              \
            'pid': 14267}}

{'execute': 'guest-file-read',               \
 'arguments': {'count': 65536,               \
               'handle': 6}}
{'return': {'buf-b64': '',                   \
            'count': 0,                      \
            'eof': False}}

{'execute': 'guest-file-read',               \
 'arguments': {'count': 65536,               \
               'handle': 6}}
{'return': {'buf-b64': 'dG9wIC0gMjI6N...',   \
            'count': 11064,                  \
            'eof': True}}

/*
top - 22:41:49 up 1 day,  4:30,  3 users,  load average: 0.00, 0.00, 0.00
Tasks: 114 total,   1 running, 113 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.2%us,  0.2%sy,  0.0%ni, 99.6%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:    504848k total,   445664k used,    59184k free,    49100k buffers
Swap:   323580k total,      224k used,   323356k free,   256392k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
14267 root      20   0 19272 1248  924 R    2  0.2   0:00.02 top
    1 root      20   0 24008 2048 1280 S    0  0.4   0:00.85 init
    2 root      20   0     0    0    0 S    0  0.0   0:00.30 kthreadd
    3 root      20   0     0    0    0 S    0  0.0   0:01.09 ksoftirqd/0
...
*/

{'execute': 'guest-exec-status',             \
 'arguments': {'pid': 14267}}
{'return': {'exit-code': 0,                  \
            'exited': True,                  \
            'handle_stderr': -1,             \
            'handle_stdin': -1,              \
            'handle_stdout': 6,              \
            'pid': 14267}}

{'execute': 'guest-file-close'}              \
 'arguments': {'handle': 6}}
{'return': {}}

Michael Roth (2):
  guest agent: add guest-file-open-pipe
  guest agent: add guest-exec and guest-exec-status interfaces

 qapi-schema-guest.json     |   79 +++++++-
 qga/guest-agent-commands.c |  478 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 531 insertions(+), 26 deletions(-)

-- 
1.7.4.1