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

[Like Xu]

On 2019/4/2 19:27, Markus Armbruster wrote:
> 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".

Thanks for your comments and this issue may not exist in this patch.

I am curious when and where we would call qdev_get_machine() before 
main() initializes current_machine and adds it to QOM store which is
called very early.