Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] vl.c: make current_machine as non-global variable

[Markus Armbruster]

Like Xu <address@hidden> writes:

> This patch makes the remaining dozen or so uses of the global
> current_machine outside vl.c use qdev_get_machine() instead,
> and then make current_machine local to vl.c instead of global.
>
> Signed-off-by: Like Xu <address@hidden>

You effectively replace

    current_machine

by

    MACHINE(qdev_get_machine())

qdev_get_machine() uses container_get(), which has a side effect: any
path component that doesn't exist already gets created as "container"
object.  In case of qdev_get_machine(), that's just "/machine".

Creating "/machine" as "container" is of course wrong.  You therefore
must not use qdev_get_machine() before main() creates "/machine".  It
does like this:

    object_property_add_child(object_get_root(), "machine",
                              OBJECT(current_machine), &error_abort);

I recently had several cases of code rearrangements explode because the
reordered code called qdev_get_machine() too early.  Makes me rather
skeptical about this patch.  To be frank, I consider qdev_get_machine()
a trap for the unwary.  container_get(), too.

If we decide using it to make current_machine static a good idea anyway,
we need to check the new uses carefully to make sure they can't run
before main() creates "/machine".