Re: [Qemu-devel] [PATCH v2 6/7] vl: Set current_machine early

[Markus Armbruster <armbru@redhat.com>]

Andreas Färber <afaerber@suse.de> writes:

> Am 16.08.2013 15:18, schrieb armbru@redhat.com:
>> From: Markus Armbruster <armbru@redhat.com>
>> 
>> I'd like to access QEMUMachine from a QEMUMachine init() method, which
>> is currently not possible.  Instead of passing it as an argument, I
>> simply set current_machine earlier.
>
> We had such a patch for CPU hot-add and decided against doing this.
> Currently current_machine != signals that it has been initialized. And

Does any code actually depend on this undocumented condition?  I found
none.

> generally we have been trying to get away from accessing globals from
> random parts of code.

Global state need to be managed with care.  Global variables have their
place in that.

In my experience, the most common kind of carelessness involving global
variables is indisciplined *updating* of global state via global
variables.

Unchanging global state is relatively harmless, and referring to it via
global variables is often the easiest and most obvious way to manage
such state.

> Can't you pass either QEMUMachine or the specific fields needed from PC
> code to those SMBIOS functions? You did add a bool argument.

Can't see how to do that without passing the machine to QEMUMachine
method init(), which involves touching all boards.  I doubt that's a
good idea, but if you insist, I can do it.