Re: [Qemu-devel] [PATCH v4 5/9] qapi: introduce new cmd option "allowed-in-preconfig"

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 28 Mar 2018 16:30:16 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Wed, Mar 28, 2018 at 02:29:57PM +0200, Igor Mammedov wrote:
> > On Fri, 23 Mar 2018 18:28:37 -0300
> > Eduardo Habkost <ehabkost@redhat.com> wrote:
> >   
> > > On Mon, Mar 12, 2018 at 02:11:11PM +0100, Igor Mammedov wrote:  
> > > > New option will be used to allow commands, which are prepared/need
> > > > to run run in preconfig state. Other commands that should be able
> > > > to run in preconfig state, should be ammeded to not expect machine
> > > > in initialized state or deal with it.
> > > > 
> > > > For compatibility reasons, commands, that don't use new flag
> > > > 'allowed-in-preconfig' explicitly, are not permited to run in
> > > > preconfig state but allowed in all other states like they used
> > > > to be.
> > > > 
> > > > Within this patch allow following commands in preconfig state:
> > > >    qmp_capabilities
> > > >    query-qmp-schema
> > > >    query-commands
> > > >    query-status
> > > >    cont
> > > > to allow qmp connection, basic introspection and moving to the next
> > > > state.
> > > > 
> > > > PS:
> > > > set-numa-node and query-hotpluggable-cpus will be enabled later in
> > > > a separate patch.
> > > > 
> > > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>    
> > > 
> > > I didn't review the code yet, but:
> > > 
> > > Shouldn't this be applied before patch 3/9, for bisectability?
> > > Otherwise it will be very easy to crash QEMU after applying patch
> > > 3/9.  
> > no, it isn't going to work.
> > This patch depends on RUN_STATE_PRECONFIG that is introduced in 3/9.
> > 
> > It could be fine to merge into 3/9 during merge, but then history
> > wise it would be difficult to read it later with 2 big and mostly
> > separate changes within one patch.  
> 
> Yeah, I don't think squashing would be the right answer.
> 
> > 
> > Considering -preconfig if off by default it shouldn't affect
> > bisectability in general so I'd keep current patch order.  
> 
> Well, it would affect bisectability if debugging a crash that
> happens using -preconfig.
> 
> The only hunk in this patch that really depends on patch 3/9
> seems to be:
> 
>   @@ -92,6 +93,13 @@ static QObject *do_qmp_dispatch(QmpCommandList *cmds, QObject *request,
>            return NULL;
>        }
>   
>   +    if (runstate_check(RUN_STATE_PRECONFIG) &&
>   +        !(cmd->options & QCO_ALLOWED_IN_PRECONFIG)) {
>   +        error_setg(errp, "The command '%s' isn't permitted in '%s' state",
>   +                   cmd->name, RunState_str(RUN_STATE_PRECONFIG));
>   +        return NULL;
>   +    }
>   +
>        if (!qdict_haskey(dict, "arguments")) {
>            args = qdict_new();
>        } else {
>   
> 
> What about moving it to patch 3/9?
By itself it won't work but with moving following hunk with it

@@ -21,7 +21,8 @@ typedef void (QmpCommandFunc)(QDict *, QObject **, Error **);
 typedef enum QmpCommandOptions
 {
     QCO_NO_OPTIONS = 0x0,
-    QCO_NO_SUCCESS_RESP = 0x1,
+    QCO_NO_SUCCESS_RESP = 1U << 0,
+    QCO_ALLOWED_IN_PRECONFIG =  1U << 1,
 } QmpCommandOptions;

it should compile and do proper check in above hunk.

I'll try to do it and see if it works.

> Or, an alternative is to move the following hunk from patch 3/9 to this patch:
> 
>   diff --git a/qapi/run-state.json b/qapi/run-state.json
>   index 1c9fff3aef..ce846a570e 100644
>   --- a/qapi/run-state.json
>   +++ b/qapi/run-state.json
>   @@ -49,12 +49,15 @@
>    # @colo: guest is paused to save/restore VM state under colo checkpoint,
>    #        VM can not get into this state unless colo capability is enabled
>    #        for migration. (since 2.8)
>   +# @preconfig: QEMU is paused before board specific init callback is executed.
>   +#             The state is reachable only if -preconfig CLI option is used.
>   +#             (Since 2.12)
>    ##
>    { 'enum': 'RunState',
>      'data': [ 'debug', 'inmigrate', 'internal-error', 'io-error', 'paused',
>                'postmigrate', 'prelaunch', 'finish-migrate', 'restore-vm',
>                'running', 'save-vm', 'shutdown', 'suspended', 'watchdog',
>   -            'guest-panicked', 'colo' ] }
>   +            'guest-panicked', 'colo', 'preconfig' ] }
>   
>    ##
>    # @StatusInfo:
> 
> Which could be an interesting idea, because the QAPI schema
> changes would be all grouped inside a single patch, and then
> followed by the actual implementation of the -preconfig option.
it won't really work as this enum generates RUN_STATE_PRECONFIG,
which is used by 3/9