Re: [PATCH v2 00/10] Kconfig vs. default devices

[Philippe Mathieu-Daudé]

On 8/2/23 20:26, Fabiano Rosas wrote:

> We currently have a situation where disabling a Kconfig might result
> in a runtime error when QEMU selects the corresponding device as a
> default value for an option. But first a disambiguation:
>
> Kconfig default::
>    a device "Foo" for which there's "config FOO default y" or "config X
>    imply FOO" in Kconfig.
>
> QEMU hardcoded default::
>    a fallback; a device "Foo" that is chosen in case no corresponding
>    option is given in the command line.
>
> The issue I'm trying to solve is that there is no link between the two
> "defaults" above, which means that when the user at build time
> de-selects a Kconfig default, either via configs/devices/*/*.mak or
> --without-default-devices, the subsequent invocation at runtime might
> continue to try to create the missing device due to QEMU defaults.

This will keep bitrotting if we don't cover such configs in our CI.

Why do you want to get this fixed BTW? I'm not sure there is a big
interest (as in "almost no users").

I tried to do that few years ago [*] and Thomas said:

"in our CI, we should test what users really need,
 and not each and every distantly possible combination."

[*] 
https://lore.kernel.org/qemu-devel/81aca179-4320-f00b-d9dc-7eca449ebce7@redhat.com/

> Fabiano Rosas (10):
>    hw/i386: Select CONFIG_PARALLEL for PC machines
>    hw/i386: Select E1000E for q35
>    hw/i386: Select VGA_PCI in Kconfig
>    hw/i386: Select E1000_PCI for i440fx
>    hw/arm: Select VIRTIO_NET for virt machine
>    hw/arm: Select VIRTIO_BLK for virt machine
>    hw/arm: Select XLNX_USB_SUBSYS for xlnx-zcu102 machine
>    hw/arm: Select GICV3_TCG for sbsa-ref machine
>    hw/arm: Select e1000e for sbsa-ref machine
>    hw/arm: Select VGA_PCI for sbsa-ref machine
>
>   hw/arm/Kconfig  | 7 +++++++
>   hw/i386/Kconfig | 8 ++++----
>   hw/usb/Kconfig  | 1 -
>   3 files changed, 11 insertions(+), 5 deletions(-)