On Tue, Aug 06, 2013 at 01:48:17PM +0200, Markus Armbruster wrote:
> Gleb Natapov <g...@redhat.com> writes:
>
> > On Tue, Aug 06, 2013 at 01:03:34PM +0200, Andreas Färber wrote:
> >> Am 06.08.2013 12:44, schrieb Gleb Natapov:
> >> > On Tue, Aug 06, 2013 at 01:19:53PM +0300, Michael S. Tsirkin wrote:
> >> >>>> It's a QEMU issue, devices that are added with -device are
> >> >>>> documented in -device help and removed by dropping them from
> >> >>>> command line. Devices added by default have no way to
> >> >>>> be dropped from QOM except -nodefaults.
> >> >>>>
> >> >>> Are you saying that because pvpanic is added automatically QEMU -device
> >> >>> help does not print help about it? Why not fix that? What QEMU --help
> >> >>> issues has to do with deciding which devices should or should not be
> >> >>> present by default?
> >> >>
> >> >> No, I'm saying what I said: that there's no way to remove a device
> >> >> added by default except -nodefaults, and no way to
> >> >> find out what does -nodefaults exclude so you
> >> >> can add things you need back selectively.
> >> >>
> >> > And what are the rules that govern device exclusion from -nodefaults
> >> > list? Why -nodefaults does not create empty machine?
> >>
> >> We have -M none to create an empty machine.
> >>
> >> FWIW -M q35 does not create all Q35 devices, there's -readconfig
> >> docs/q35-chipset.cfg for the rest. The criteria certainly is not
> >> migratability, since ICH9 AHCI (part of -M q35) is unmigratable,
> >> unfortunately.
> >> One practical reason not to create everything via config is that we
> >> cannot create SysBusDevices via -device when they require MMIO mapping
> >> or IRQ setup.
>
> Support wiring up a machine without board code, just configuration has
> been the ever-distant goal of the qdev effort.
>
> >> For ISADevices such as pvpanic that's not a problem.
> >> Anthony has proposed QOM'ifying MemoryRegions and qemu_irq as solution
> >> to do the wiring-up from command line or config file, but those attempts
> >> got stuck a long time ago.
> >>
> > But -M creates not only things that cannot be created from a command
> > line, it includes some default set of devices, so what is the criteria
> > for those?
>
> I'm not aware of defined, coherent criteria.
>
> I can give you descriptive rather than prescriptive, though. Used to be
> "whatever anyone felt users would want". It's now "whatever has always
> been there, plus whatever survives interminable bikeshedding^W^Wvigorous
> debate.
No need to for ^W! It is like disputes in court: whoever has more
money wins. In out case whoever has more times wins and I am going on
vocation, so... :)
--
Gleb.
