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

[Markus Armbruster]

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.

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