Re: [Qemu-devel] [PATCH] New API for asynchronous monitor commands (V2)

[Kevin Wolf <kwolf@redhat.com>]

Am 25.01.2010 19:18, schrieb Adam Litke:
> Changes since V1:
>  - Miscellaneous code cleanups (Thanks Luiz)
> 
> Qemu has a number of commands that can operate asynchronously (savevm, migrate,
> etc) and it will be getting more.  For these commands, the user monitor needs
> to be suspended, but QMP monitors could continue to to accept other commands.
> This patch introduces a new command API that isolates the details of handling
> different monitor types from the actual command execution.
> 
> A monitor command can use this API by implementing the mhandler.cmd_async
> handler (or info_async if appropriate).  This function is responsible for
> submitting the command and does not return any data although it may raise
> errors.  When the command completes, the QMPCompletion callback should be
> invoked with its opaque data and the command result.
> 
> The process for submitting and completing an asynchronous command is different
> for QMP and user monitors.  A user monitor must be suspended at submit time and
> resumed at completion time.  The user_print() function must be passed to the
> QMPCompletion callback so the result can be displayed properly.  QMP monitors
> are simpler.  No submit time setup is required.  When the command completes,
> monitor_protocol_emitter() writes the result in JSON format.
> 
> This API can also be used to implement synchronous commands.  In this case, the
> cmd_async handler should immediately call the QMPCompletion callback.  It is my
> hope that this new interface will work for all commands, leading to a
> drastically simplified monitor.c once all commands are ported.
> 
> Thanks to Anthony for helping me out with the initial design.
> 
> Signed-off-by: Adam Litke <agl@us.ibm.com>

This commit introduces a segfault on info pci for me. The following
patch seems to make it work again. Is it correct or is rather info pci
doing something wrong?

diff --git a/monitor.c b/monitor.c
index fbae5ce..22690c4 100644
--- a/monitor.c
+++ b/monitor.c
@@ -3700,7 +3700,12 @@ static void monitor_print_error(Monitor *mon)

 static int is_async_return(const QObject *data)
 {
-    return data && qdict_haskey(qobject_to_qdict(data), "__mon_async");
+    const QDict *dict = NULL;
+
+    if (data != NULL) {
+        dict = qobject_to_qdict(data);
+    }
+    return dict && qdict_haskey(dict, "__mon_async");
 }

 static void monitor_call_handler(Monitor *mon, const mon_cmd_t *cmd,

Kevin