Re: [PATCH 05/22] hw/arm: Select VIRTIO_NET for virt machine

[Fabiano Rosas]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 5/3/23 11:12, Alex Bennée wrote:
>> From: Fabiano Rosas <farosas@suse.de>
>> 
>> The 'virt' machine uses virtio-net-pci as a fallback when no other
>> network driver has been selected via command line. Select VIRTIO_NET
>> and VIRTIO_PCI from CONFIG_ARM_VIRT to avoid errors when PCI_DEVICES=n
>> (due to e.g. --without-default-devices):
>> 
>> $ ./qemu-system-aarch64 -M virt -accel tcg -cpu max
>> qemu-system-aarch64: Unsupported NIC model: virtio-net-pci
>
> With respect to patches 5-17, very few devices need to be present when 
> configuring --without-default-devices, and thus need to be "select"ed by 
> Kconfig.  You should select a device only if you cannot even start the 
> machine without --nodefaults.
>

There are some devices that are not explicitly under the scope of
-nodefaults, i.e. they are not part of the "default" logic at vl.c, but
still some code deep within QEMU uses them as fallback in some
situations.

> Anything else should be added by hand to configs/ if you use 
> --nodefaults.  In particular, failures of "make check" when configured 
> --without-default-devices are *test* bugs, not configuration bugs.
>

Yes, that makes sense, just keep in mind that this have lead to us not
testing the --without-default-devices build and people just assuming
some devices will always be present. So there's genuine scenarios of us
providing a CONFIG that can never be turned off because everything
breaks.