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Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] vl.c: make current_machine as
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] vl.c: make current_machine as non-global variable |
Date: |
Tue, 2 Apr 2019 17:47:49 +0200 |
On Tue, 2 Apr 2019 21:09:39 +0800
Like Xu <address@hidden> wrote:
> 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".
maybe we can assert in qdev_get_machine() if machine hasn't been created yet?
with this at least it will be hard to misuse function or catch invalid users.
(but it still might miss some use cases/CLI options which are not tested)
> >
>
> 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.