docs: Correct outdated information on QAPI

For all the examples in the next sections, the test setup is the same and is

shown here.

First, QEMU should be started as:

First, QEMU should be started like this:

# /path/to/your/source/qemu [...] \

# qemu-system-TARGET [...] \

    -chardev socket,id=qmp,port=4444,host=localhost,server \

    -mon chardev=qmp,mode=control,pretty=on

    }

}

You should see "Hello, world" and "we love qemu" in the terminal running qemu,

You should see "Hello, world" and "We love qemu" in the terminal running qemu,

if you don't see these strings, then something went wrong.

=== Errors ===

    }

}

As a general rule, all QMP errors should use ERROR_CLASS_GENERIC_ERROR

(done by default when using error_setg()). There are two exceptions to

this rule:

Note that error_setg() produces a "GenericError" class.  In general,

all QMP errors should have that error class.  There are two exceptions

to this rule:

 1. A non-generic ErrorClass value exists* for the failure you want to report

    (eg. DeviceNotFound)

 1. To support a management application's need to recognize a specific

    error for special handling

 2. Management applications have to take special action on the failure you

    want to report, hence you have to add a new ErrorClass value so that they

    can check for it

 2. Backward compatibility

If the failure you want to report falls into one of the two cases above,

use error_set() with a second argument of an ErrorClass value.

 * All existing ErrorClass values are defined in the qapi-schema.json file

=== Command Documentation ===

There's only one step missing to make "hello-world"'s implementation complete,

and that's its documentation in the schema file.

This is very important. No QMP command will be accepted in QEMU without proper

documentation.

There are many examples of such documentation in the schema file already, but

here goes "hello-world"'s new entry for qapi/misc.json:

    }

}

Please, refer to the qapi-schema.json file for a complete command reference.

Please refer to docs/interop/qemu-qmp-ref.* for a complete command

reference, generated from qapi-schema.json.

QMP wiki page

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