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.
