On 05/22/2015 05:36 AM, Markus Armbruster wrote: > The asynchronous monitor command interface goes back to commit 940cc30 > (Jan 2010). Added a third case to command execution. The hope back > then according to the commit message was that all commands get > converted to the asynchronous interface, killing off the other two > cases. Didn't happen. > > The initial asynchronous commands balloon and info balloon were > converted back to synchronous long ago (commit 96637bc and d72f32), > with commit messages calling the asynchronous interface "not fully > working" and "deprecated". The only other user went away in commit > 3b5704b.
The history is helpful; thanks.
>
> New code generally uses synchronous commands and asynchronous events.
>
> What exactly is still "not fully working" with asynchronous commands?
> Well, here's a bug that defeats actual asynchronous use pretty
> reliably: the reply's ID is wrong (and has always been wrong) unless
> you use the command synchronously! To reproduce, we need an
> asynchronous command, so we have to go back before the commit 3b5704b.
> Run QEMU with spice:
>
> $ qemu-system-x86_64 -nodefaults -S -spice port=5900,disable-ticketing
> -qmp stdio
> {"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major":
> 2}, "package": ""}, "capabilities": []}}
>
> Connect a spice client in another terminal:
>
> $ remote-viewer spice://localhost:5900
>
> Set up a migration destination dummy in a third terminal:
>
> $ socat TCP-LISTEN:12345 STDIO
>
> Now paste the following into the QMP monitor:
>
> { "execute": "qmp_capabilities" }
If you stick and "id":"i0" here...
> { "execute": "client_migrate_info", "id": "i1", "arguments": {
> "protocol": "spice", "hostname": "localhost", "port": 12345 } }
> { "execute": "query-kvm", "id": "i2" }
>
> Produces two replies immediately, one to qmp_capabilities, and one to
> query-kvm:
>
> {"return": {}}
...it should show up here, for even less ambiguity about the problems
with the async response.
> {"return": {"enabled": false, "present": true}, "id": "i2"}
>
> Both are correct. Two lines of debug output from libspice-server not
> shown.
>
> Now EOF socat's standard input to make it close the connection. This
> makes the asynchronous client_migrate_info complete. It replies:
>
> {"return": {}}
>
> Bug: "id": "i1" is missing. Two lines of debug output from
> libspice-server not shown. Cherry on top: storage for the missing ID
> is leaked.
>
> Get rid of this stuff before somebody hurts himself with it.
>
> Signed-off-by: Markus Armbruster <arm...@redhat.com>
> ---
> include/monitor/monitor.h | 5 ----
> monitor.c | 68
> ++---------------------------------------------
> 2 files changed, 2 insertions(+), 71 deletions(-)
Certainly takes an axe to it!
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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