Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> writes: > On 30/04/2020 15:11, Markus Armbruster wrote: > >> Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> writes: >> >>> On 30/04/2020 11:03, Markus Armbruster wrote: >>>> Peter Maydell <peter.mayd...@linaro.org> writes: >>>> >>>>> On Thu, 30 Apr 2020 at 08:09, Markus Armbruster <arm...@redhat.com> wrote: >>>>>> Our means to configure onboard devices are weak. We sidestepped this >>>>>> for isa-fdc by taking it off the board, and thus make -device work. >>>>> >>>>> This seems to be a general dynamic: the x86 pc machine works >>>>> via -device options (or is changed so it can work that way); >>>>> and then people propose dropping/deprecating/etc the config >>>>> options that work with onboard devices, without providing >>>>> clear solutions/instructions on how the command line needs >>>>> to change/etc for the mass of boards which are not the x86 >>>>> pc machine and which do have a lot of onboard devices which >>>>> can't be handled via -device. >>>>> >>>>> So my gut reaction to the "we should deprecate -global" >>>>> suggestions in this thread was a bit "here we go again"... >>>>> What works for x86 or even "what is sufficient for libvirt" >>>>> doesn't necessarily cover all the cases. >>>> >>>> Such shortsighted proposals have been made, but don't think it's what >>>> we're doing here. >>>> >>>> You're 100% right in that we do need to configure onboard devices. >>>> -global is a terrible way to do it, though: it applies to *all* devices >>>> of a kind. What if the board has more than one? What if the can add >>>> more? >>>> >>>> Taking onboard devices off the board can occasionally sidestep the >>>> issue. For isa-fdc, we genuinely *wanted* to take the damn thing off, >>>> because all it did for most users was provide them with VENOM. Not >>>> needing -global for it anymore was just a nice bonus. >>>> >>>> Taking onboard devices off just to reduce the device configuration >>>> problem to a solved one, namely -device, may be tempting (it was to me), >>>> but it's too intrusive to be practical at scale. >>>> >>>> Adding machine properties that alias onboard device properties is less >>>> intrusive. The ones I added were still a lot of work. >>>> >>>> Configuring onboard devices via machine properties restricts property >>>> access to the ones we added to the machine. This differs from pluggable >>>> devices, where users can access all properties. >>>> >>>> Any better ideas for letting users configure onboard devices? >>> >>> Is it possible to let machine owners add alias properties to the machine >>> object >>> referencing in-built devices? I could then instantiate my on-board nic in >>> the machine >>> init() function, and then use object_property_add_alias() to add a "nic0" >>> alias on >>> the machine that can be used to wire it up to a netdev using the command >>> line. >> >> Have a look at hw/arm/virt.c's virt_flash_create(), from commit >> e0561e60f1 "hw/arm/virt: Support firmware configuration with -blockdev". >> It adds machine properties "pflash0" and "pflash1" as aliases for the >> onboard flash memory devices' property "drive". >> >> Does this answer your question? > > Ah I see now, these aliases are for individual properties rather than > objects. What I > was trying to ask was if it were possible to have something like this: > > /machine (SS-5-machine) > /builtin > /nic0 -> link to "lance" device > > Here nic0 is an alias "published" by the maintainer of the SS-5 machine which > is > configured in the machine init() function using object_property_add_link() or > a > suitable wrapper. Users can then configure these builtin devices from the > command > line using your -machine nic0.netdev=my-netdev-id syntax or similar.
Got it now, thanks! > Having the default devices under /builtin or other known QOM path would enable > builtin devices to be easily enumerated programatically and/or from the > command line > as required. There are three standard containers under /machine/: * /machine/peripheral/ Devices with a user-specified ID go here, as /machine/peripheral/ID. User-specified means -device or device_add. /machine/peripheral/ID is effectively a stable interface. It's just underdocumented (undocumented?). To be useful, the stuff below ID/ needed to be stable and documented, too. * /machine/peripheral-anon/ Same, but user elected not to give an ID. /machine/peripheral-anon/device[N], where N counts up from zero in creation order. N is obviously not stable, but this is a problem of the user's making. If you want to refer to a device, give it an ID. * /machine/unattached/ The orphanage. When a device has no parent when its realized, it gets put here, as /machine/unattached/device[N], where N counts up from zero in realization order. N is obviously not stable, and this time we can't blame the victim^Wuser. You can search for devices of a certain type. Sometimes that's good enough. All the onboard devices are here, and much more. We've fathered a lot of unloved red-headed children, it seems... Some of the "much more" is due to sloppy modelling, i.e. neglecting to set the proper parent. I figure we could put onboard devices in a nicer place, with nicer names. Need a convention for the place and the names, then make board code conform to it.
