qemu-trivial
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


From: Markus Armbruster
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] vl.c: make current_machine as non-global variable
Date: Tue, 02 Apr 2019 18:13:07 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Igor Mammedov <address@hidden> writes:

> 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)

Good idea.  When my code created "/machine" as a container, debugging
the resulting crash took me a bit of time.  The assertion you propose
would've saved me some.



reply via email to

[Prev in Thread] Current Thread [Next in Thread]