linux-kernel - Re: [PATCH RESEND v2] kunit: Enable PCI on UML without triggering WARN()

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Message-ID: <CAMuHMdX6raywNiuDG0zzYQu35YpfSHoE4KSsJLcDfeSqZAac+Q@mail.gmail.com>
Date: Mon, 8 Sep 2025 18:53:30 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, Richard Weinberger <richard@....at>, 
	Anton Ivanov <anton.ivanov@...bridgegreys.com>, Johannes Berg <johannes@...solutions.net>, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, linux-um@...ts.infradead.org
Subject: Re: [PATCH RESEND v2] kunit: Enable PCI on UML without triggering WARN()

Hi Thomas,

On Mon, 8 Sept 2025 at 09:04, Thomas Weißschuh
<thomas.weissschuh@...utronix.de> wrote:
> Various KUnit tests require PCI infrastructure to work. All normal
> platforms enable PCI by default, but UML does not. Enabling PCI from
> .kunitconfig files is problematic as it would not be portable. So in
> commit 6fc3a8636a7b ("kunit: tool: Enable virtio/PCI by default on UML")
> PCI was enabled by way of CONFIG_UML_PCI_OVER_VIRTIO=y. However
> CONFIG_UML_PCI_OVER_VIRTIO requires additional configuration of
> CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID or will otherwise trigger a WARN() in
> virtio_pcidev_init(). However there is no one correct value for
> UML_PCI_OVER_VIRTIO_DEVICE_ID which could be used by default.
>
> This warning is confusing when debugging test failures.
>
> On the other hand, the functionality of CONFIG_UML_PCI_OVER_VIRTIO is not
> used at all, given that it is completely non-functional as indicated by
> the WARN() in question. Instead it is only used as a way to enable
> CONFIG_UML_PCI which itself is not directly configurable.
>
> Instead of going through CONFIG_UML_PCI_OVER_VIRTIO, introduce a custom
> configuration option which enables CONFIG_UML_PCI without triggering
> warnings or building dead code.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> Reviewed-by: Johannes Berg <johannes@...solutions.net>

Thanks for your patch!

> --- a/lib/kunit/Kconfig
> +++ b/lib/kunit/Kconfig
> @@ -106,4 +106,11 @@ config KUNIT_DEFAULT_TIMEOUT
>           If unsure, the default timeout of 300 seconds is suitable for most
>           cases.
>
> +config KUNIT_UML_PCI

Where is the consumer of this symbol?

> +       bool "KUnit UML PCI Support"
> +       depends on UML
> +       select UML_PCI
> +       help
> +         Enables the PCI subsystem on UML for use by KUnit tests.
> +
>  endif # KUNIT
> diff --git a/tools/testing/kunit/configs/arch_uml.config b/tools/testing/kunit/configs/arch_uml.config
> index 54ad8972681a2cc724e6122b19407188910b9025..28edf816aa70e6f408d9486efff8898df79ee090 100644
> --- a/tools/testing/kunit/configs/arch_uml.config
> +++ b/tools/testing/kunit/configs/arch_uml.config
> @@ -1,8 +1,7 @@
>  # Config options which are added to UML builds by default
>
> -# Enable virtio/pci, as a lot of tests require it.
> -CONFIG_VIRTIO_UML=y
> -CONFIG_UML_PCI_OVER_VIRTIO=y
> +# Enable pci, as a lot of tests require it.
> +CONFIG_KUNIT_UML_PCI=y
>
>  # Enable FORTIFY_SOURCE for wider checking.
>  CONFIG_FORTIFY_SOURCE=y

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds