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Re: [Qemu-devel] [QAPI+QGA 3/3] QEMU Guest Agent (virtagent) v6


From: Michael Roth
Subject: Re: [Qemu-devel] [QAPI+QGA 3/3] QEMU Guest Agent (virtagent) v6
Date: Thu, 14 Jul 2011 09:04:30 -0500
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:5.0) Gecko/20110624 Thunderbird/5.0

On 07/14/2011 08:53 AM, Zhi Yong Wu wrote:
On Thu, Jul 14, 2011 at 8:55 PM, Luiz Capitulino<address@hidden>  wrote:
On Thu, 14 Jul 2011 10:53:51 +0800
Zhi Yong Wu<address@hidden>  wrote:

HI, Michael,

On Tue, Jul 5, 2011 at 9:21 PM, Michael Roth<address@hidden>  wrote:
This is Set 3/3 of the QAPI+QGA patchsets.

These patches apply on top of qapi-backport-set2-v5, and can also be obtained 
from:
git://repo.or.cz/qemu/mdroth.git qapi-backport-set3-v6

(Set1+2 are a backport of some of the QAPI-related work from Anthony's
glib tree. The main goal is to get the basic code generation infrastructure in
place so that it can be used by the guest agent to implement a QMP-like guest
interface, and so that future work regarding the QMP conversion to QAPI can be
decoupled from the infrastructure bits. Set3 is the Qemu Guest Agent
(virtagent), rebased on the new code QAPI code generation infrastructure. This
is the first user of QAPI, QMP will follow.)
___

CHANGES SINCE V5:
  - switched to using qemu malloc/list functions where possible
  - removed unused proxy_path field in struct GAState
  - pid file now opened write-only, removed lockf() in favor of O_EXCL, added 
SIGINT/SIGTERM signal handlers to handle cleanup
  - cleaned up error-handling, switched to asserts where appropriate, removed 
unecessary gotos and NULL checks for qemu_free()/qobject_decref()
  - refactored send_payload() using helper functions
  - fixed improper handling of pidfile fd==0
  - changed guest-shutdown's "shutdown_mode" param to "mode"
  - switched to using kernel-generated FDs for guest-file-open rather than an 
autoincrement value
  - add maximum chunk size of guest-file-read/guest-file-write
  - added checks to avoid guest-file-write from writing data beyond the 
provided data buffer
  - made logging best-effort, removed handling of failures to log as errors
  - guest-shutdown exec errors now logged to guest syslog, clarified shutdown's 
asynchronous, no gauruntee nature in schema.

CHANGES SINCE V4:
  - Removed timeout mechanism via worker thread/pthread_cancel due to potential 
memory leak. Will re-introduce guest-side timeout support in future version.
  - Fixed up fsfreeze code to use enums specified within the guest agent's qapi 
schema.
  - Fixed memory leak due to a log statement, and added missing cleanup 
functions for heap-allocated g_error objects.
  - Made "mode" param to guest-file-open optional, defaults to "r" (read-only)

CHANGES SINCE V3:
  - Fixed error-handling issues in fsfreeze commands leading to certain mounted 
directories causing freeze/thaw operations to fail
  - Added cleanup hook to thaw filesystems on graceful guest agent exit
  - Removed unused enum values and added additional details to schema 
documentation
  - Fixed build issue that was missed due to deprecated files in source tree, 
removed unused includes

CHANGES SINCE V2:
  - Rebased on new QAPI code generation framework
  - Dropped ability for QMP to act as a proxy for the guest agent, will be 
added when new QMP server is backported from Anthony's glib tree
  - Replaced negotiation/control events with a simple 2-way handshake 
implemented by a standard RPC (guest-sync)
  - Removed enforcement of "pristine" sessions, state is now global/persistant 
across multiple clients/connections
  - Fixed segfault in logging code
  - Added Jes' filesystem freeze patches
  - General cleanups

CHANGES SINCE V1:
  - Added guest agent worker thread to execute RPCs in the guest. With this in 
place we have a reliable timeout mechanism for hung commands, currently set at 
30 seconds.
  - Add framework for registering init/cleanup routines for stateful RPCs to 
clean up after themselves after a timeout.
  - Added the following RPCs: guest-file-{open,close,read,write,seek}, 
guest-shutdown, guest-info, and removed stubs for guest-view-file (now 
deprecated)
  - Added GUEST_AGENT_UP/GUEST_AGENT_DOWN QMP events
  - Switched to a TCP-style host-initiated 3-way handshake for channel 
negotiation, this simplifies client negotiation/interaction over the wire
  - Added configurable log level/log file/pid file options for guest agent
  - Various fixes for bugs/memory leaks and checkpatch.pl fixups

ISSUES/TODOS:
  - Add unit tests for guest agent wire protocol

OVERVIEW

For a better overview of what these patches are meant to accomplish, please 
reference the RFC for virtagent:

http://comments.gmane.org/gmane.comp.emulators.qemu/96096

These patches integrate the previous virtagent guest agent work directly in 
QAPI/QMP to leverage it's auto-generated marshalling code. This has numerous 
benefits:

  - addresses previous concerns over relying on external libraries to handle 
data encapsulation
  - reduces the need for manual unmarshalling of requests/responses, which 
makes adding new RPCs much safer/less error-prone, as well as cutting down on 
redundant code
  - QAPI documentation aligns completely with guest-side RPC implementation
  - is Just Better (TM)

BUILD/USAGE

build:
  ./configure --target-list=x86_64-softmmu
  make
  make qemu-ga #should be built on|for target guest

start guest:
  qemu \
  -drive file=/home/mdroth/vm/rhel6_64_base.raw,snapshot=off,if=virtio \
  -net nic,model=virtio,macaddr=52:54:00:12:34:00 \
  -net tap,script=/etc/qemu-ifup \
  -vnc :1 -m 1024 --enable-kvm \
  -chardev socket,path=/tmp/qga.sock,server,nowait,id=qga \
  -device virtio-serial \
  -device virtserialport,chardev=qga,name=qga"

use guest agent:
  ./qemu-ga -h
  ./qemu-ga -c virtio-serial -p /dev/virtio-ports/qga
Is the above command "./qemu-ga" issued on guest teminal or hypervisor teminal?

In the guest.

Can we make it work similiar as a linux service? It may is more
convenient to use.

address@hidden ~]# service qemu-ga start/stop/status/restart

address@hidden ~]# chkconfig qemu-ga on/off


Definitely, we need the agent to act as a service to be able to rely on it remaining after restarts and whatnot. We have some init scripts and whatnot for in-house testing/deployment, but this is somewhat distro-dependent and is more of a packaging concern than something for qemu-devel.

Although, if we do deployment via the guest tools ISO that I sent an RFC out for a while back, it may be worthwhile to cover this as part of that discussion since ideally we'd come up with something that Just Works on most distros. I hope to have a prototype of ISO generation scripts out within the next week or so.




start/use qmp:
  address@hidden:~$ sudo socat unix-connect:/tmp/qga.sock readline
  {"execute":"guest-sync", "arguments":{"id":1234}}
  {"return": 1234}

  {"execute":"guest-info"}
  {"return": {}}

  {"execute": "guest-info"}
  {"return": {"version": "1.0"}}

  {"execute":"guest-file-open", 
"arguments":{"filepath":"/tmp/testqga","mode":"w+"}}
  {"return": 0}
  {"execute":"guest-file-write", 
"arguments":{"filehandle":0,"data_b64":"aGVsbG8gd29ybGQhCg==","count":13}} // writes "hello 
world!\n"
  {"return": {"count": 13, "eof": false}}

  {"execute":"guest-file-open", 
"arguments":{"filepath":"/tmp/testqga","mode":"r"}}
  {"return": 1}
  {"execute":"guest-file-read", "arguments":{"filehandle":1,"count":1024}}
  {"return": {"buf": "aGVsbG8gd29ybGQhCg==", "count": 13, "eof": true}}
  {"execute":"guest-file-close","arguments":{"filehandle":1}}
  {"return": {}}

  Makefile                        |   22 +-
  configure                       |    1 +
  qapi-schema-guest.json          |  202 +++++++++++++
  qemu-ga.c                       |  631 +++++++++++++++++++++++++++++++++++++++
  qerror.c                        |    4 +
  qerror.h                        |    3 +
  qga/guest-agent-command-state.c |   73 +++++
  qga/guest-agent-commands.c      |  522 ++++++++++++++++++++++++++++++++
  qga/guest-agent-core.h          |   30 ++
  9 files changed, 1483 insertions(+), 5 deletions(-)












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