Re: [Qemu-devel] QEMU and Kconfig

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/11/2018 14:06, Eduardo Habkost wrote:
> On Thu, Nov 08, 2018 at 10:55:21AM +0100, Paolo Bonzini wrote:
>> On 07/11/2018 20:30, Thomas Huth wrote:
>>> On 2018-11-07 20:24, Eduardo Habkost wrote:
>>>> On Wed, Nov 07, 2018 at 06:39:54PM +0100, Paolo Bonzini wrote:
>>>>> On 07/11/2018 16:41, Samuel Ortiz wrote:
>>>>>> - The Kconfig parser would be used to generate the equivalent of what we
>>>>>>   currently have under default-configs/
>>>
>>> I think we would still have something like default-configs - but there
>>> would only be the bare minimum config switches in there, the rest would
>>> be pulled in by dependencies.
>>
>> Yes, in theory default-configs would end up empty, except for possibly
>> some commented lines to show the "default y" symbols for the target.
>>
>>> We could then also even have multiple config directories:
>>>
>>> ./configs
>>>  +-------/default-softmmu
>>>  +-------/default-linux-user
>>>  +-------/nemu (or lean-kvm or something similar)
>>>  +...
>>>
>>> ... just my 0.02 €, feel free to ignore that idea ;-)
>>
>> Yup, one can also think of a configure option like "./configure
>> --with-device-config=configs/nemu/" to pick up the alternative
>> configurations.
>>
>>>> Also, I would like to eventually replace many ./configure options
>>>> with options read from a build configuration file.
>>>>
>>>> Distributions often have huge ./configure command lines in their
>>>> QEMU packages, and they could be replaced by simple build
>>>> configuration files.
>>>>
>>>> Having a mode that requires all build options to be specified
>>>> explicitly (instead of silently picking a default) would be
>>>> useful for distributions, too.
>>>
>>> I think we should maybe not mix host configuration (via ./configure) and
>>> the target configuration (via kconfig), should we?
>>
>> Yeah, the configure command line is a different story.  If there are
>> suggestion on how to improve it, great, but let's not conflate it with
>> Kconfig.
> 
> I believe we have many ./configure options that are supposed to
> be target configuration.  e.g.: --enable-slirp, --eanble-kvm,
> --enable-xen, etc.

SLIRP is not a target configuration, it's a backend like most other
configure command line options.  The accelerators are but (except for
TCG of course) they also depend on the host OS and architecture, which
makes them a bit more complicated than default-configs/ symbols.  There
are also things like --enable-vhost-user which affect the creation of
both devices (e.g. vhost-user-scsi-pci) and backends (e.g. the
vhost-user-net backend, which uses a "regular" virtio-net-pci device).

It would surely be possible for configure to call into minikconf to
parse a configuration file and apply dependencies (do we actually have
dependencies across configure options?) or something like that, but
let's not put the cart before the horse...

Paolo