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Re: Difference between 'current_machine' vs MACHINE(qdev_get_machine())
From: |
Paolo Bonzini |
Subject: |
Re: Difference between 'current_machine' vs MACHINE(qdev_get_machine()) |
Date: |
Thu, 9 Jan 2020 13:01:30 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 |
On 09/01/20 12:23, Philippe Mathieu-Daudé wrote:
>
>
> current_machine =
> MACHINE(object_new_with_class(OBJECT_CLASS(machine_class)));
> object_property_add_child(object_get_root(), "machine",
> OBJECT(current_machine), &error_abort);
>
> The bigger user of 'current_machine' is the accel/KVM code.
>
> Recently in a0628599f..cc7d44c2e0 "Replace global smp variables with
> machine smp properties" we started to use MACHINE(qdev_get_machine()).
>
> qdev_get_machine() resolves the machine in the QOM composition tree.
> I am confused by this comment:
>
> /* qdev_get_machine() can return something that's not TYPE_MACHINE
> * if this is one of the user-only emulators; in that case there's
> * no need to check the ignore_memory_transaction_failures board flag.
> */
>
> Following a0628599f..cc7d44c2e0, a5e0b33119 use 'current_machine' again.
>
> What are the differences between both form, when should we use one or
> another (or can we use a single one?). Can this break user-only mode?
I would always use MACHINE(qdev_get_machine()), espeecially outside
vl.c. Ideally, current_machine would be static within vl.c or even
unused outside the object_property_add_child() that you quote above.
Most of the times, I noticed from a quick grep, we actually want to
access the accelerator, not the machine, so we could add a
qemu_get_accelerator() wrapper that does
MACHINE(qdev_get_machine())->accelerator.
Paolo