Re: [Qemu-devel] [RFC][PATCH v2 00/11] QEMU Guest Agent: QMP-based host/guest communication (virtagent)

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

On 04/21/2011 04:46 AM, Jes Sorensen wrote:
> On 04/18/11 17:02, Michael Roth wrote:
>> These apply on top of Anthony's glib tree, commit 03d5927deb5e6baebaade1b4c8ff2428a85e125c currently, and can also be obtained from:
>> git://repo.or.cz/qemu/mdroth.git qga_v2
>>
>> Patches 1-8 are general json/QAPI-related fixes. Anthony, please consider pulling these into your glib tree. The json fix-ups may need further evaluation, but I'm confident they're at least an improvement. The QAPI ones are mostly trivial fix-ups.
>>
>> 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:
>>
>> - Fix QMP proxy handling of error responses sent by guest agent, currently ignored
>> - Add unit tests for guest agent wire protocol
>> - Add unit tests for QMP interfaces
>> - Add host-side timeout mechanism for async QMP commands
>> - Return error for guest commands if guest up event has not yet been recieved
>> - Make QMP param names more consistent between related commands
>> - Clean up logging
>>
>
> Hi,
>
> I had a look through this patchset and generally it looks pretty good.
> There were a few nits, and I ignored all the python gibberish to avoid
> getting a headache.
>
> Did you do anything with the fsfreeze patches, or were they dropped in
> the migration to qapi?

They were pending some changes required on the agent side that weren't 
really addressed/doable until this patchset, namely:

1) server-side timeout mechanism to recover from RPCs that can hang 
indefinitely or take a really long time (fsfreeze, fopen, etc), 
currently it's 30 seconds, may need to bump it to 60 for fsfreeze, or 
potentially add an RPC to change the server-side timeout
2) a simple way to temporarily turn off logging so agent doesn't 
deadlock itself
3) a way to register a cleanup handler when a timeout occurs.
4) disabling RPCs where proper accounting/logging is required 
(guest-open-file, guest-shutdown, etc)

#4 isn't implemented...I think this could be done fairly in-evasively 
with something like:

Response important_rpc():
   if (!ga_log("syslog", LEVEL_CRITICAL, "important stuff happening"))
     return ERROR_LOGGING_CURRENTLY_DISABLED
   ...

bool ga_log(log_domain, level, msg):
   if (log_domain == "syslog")
     if (!logging_enabled && is_critical(log_level))
       return False;
     syslog(msg, ...)
   else
     if (logging_enabled)
       normallog(msg, ...)
   return True

With that I think we could actually drop the fsfreeze stuff in. Thoughts?

>
> Cheers,
> Jes
>