Re: [Qemu-devel] [PATCH 2/3] QMP: Introduce Human Monitor passthrough command

[Markus Armbruster]

Luiz Capitulino <address@hidden> writes:

> On Thu, 11 Nov 2010 16:47:41 +0100
> Markus Armbruster <address@hidden> wrote:
>
>> Luiz Capitulino <address@hidden> writes:
>> 
>> > On Wed, 10 Nov 2010 14:20:12 +0100
>> > Markus Armbruster <address@hidden> wrote:
>> >
>> >> Luiz Capitulino <address@hidden> writes:
>> [...]
>> >> > diff --git a/qmp-commands.hx b/qmp-commands.hx
>> >> > index 793cf1c..b344096 100644
>> >> > --- a/qmp-commands.hx
>> >> > +++ b/qmp-commands.hx
>> >> > @@ -761,6 +761,51 @@ Example:
>> >> >  
>> >> >  Note: This command must be issued before issuing any other command.
>> >> >  
>> >> > +EQMP
>> >> > +
>> >> > +    {
>> >> > +        .name       = "hmp_passthrough",
>> >> > +        .args_type  = "command-line:s,cpu-index:i?",
>> >> > +        .params     = "",
>> >> > +        .help       = "",
>> >> > +        .user_print = monitor_user_noop,
>> >> > +        .mhandler.cmd_new = do_hmp_passthrough,
>> >> > +    },
>> >> > +
>> >> > +SQMP
>> >> > +hmp_passthrough
>> >> > +---------------
>> >> > +
>> >> > +Execute a Human Monitor command.
>> >> > +
>> >> > +Arguments: 
>> >> > +
>> >> > +- command-line: the command name and its arguments, just like the
>> >> > +                Human Monitor's shell (json-string)
>> >> > +- cpu-index: select the CPU number to be used by commands which access 
>> >> > CPU
>> >> > +             data, like 'info registers'. The Monitor selects CPU 0 if 
>> >> > this
>> >> > +             argument is not provided (json-int, optional)
>> >> > +
>> >> > +Example:
>> >> > +
>> >> > +-> { "execute": "hmp_passthrough", "arguments": { "command-line": 
>> >> > "info kvm" } }
>> >> > +<- { "return": "kvm support: enabled\r\n" }
>> >> > +
>> >> > +Notes:
>> >> > +
>> >> > +(1) The Human Monitor is NOT an stable interface, this means that 
>> >> > command
>> >> > +    names, arguments and responses can change or be removed at ANY 
>> >> > time.
>> >> > +    Applications that rely on long term stability guarantees should NOT
>> >> > +    use this command
>> >> > +
>> >> > +(2) Limitations:
>> >> > +
>> >> > +    o This command is stateless, this means that commands that depend
>> >> > +      on state information (such as getfd) might not work
>> >> > +
>> >> > +    o Commands that prompt the user for data (eg. 'cont' when the block
>> >> > +      device is encrypted) don't currently work
>> >> > +
>> >> >  3. Query Commands
>> >> >  =================
>> >> 
>> >> In the real human monitor, cpu-index is state (Monitor member mon_cpu).
>> >> For pass through, you shift that state into the client (argument
>> >> cpu-index).  Is there any other state that could need shifting?  You
>> >> mention getfd.
>> >
>> > Surprisingly or not, this is a very important question for QMP itself.
>> >
>> > Anthony has said that we should make it stateless, and I do think this
>> > is good because it seems to simplify things considerably.
>> >
>> > However, I haven't thought about how to make things like getfd stateless.
>> 
>> Hmm, that sounds like we should investigate the getfd problem sooner
>> rather than later.
>
> Absolutely, but this shouldn't prevent this series of being merged, right?

Right.