On Fri, Jun 01, 2012 at 02:52:56PM +0200, Jan Kiszka wrote: > On 2012-05-30 22:31, Michael S. Tsirkin wrote: > >>> So we'll just have PIIX_NUM_PIC_IRQS entries there and use > >>> irq_count instead of the pic_levels bitmap. > >> > >> Just that this affects generic PCI code, not only PIIX-specific things. > > > > Yes but it's not a problem - pci_bus_irqs sets the map function and nirqs. > > > >> And that we need to save/restore some irq_count field according to the > >> old semantics. > > > > Well, it's a bug: this is redundant info we should not have exposed it. > > > > Anyway, let's make the rest work properly and cleanly first, add a FIXME > > for now, then we'll find a hack making it work for migration. > > It remains non-trivial: I got your patch working (a minor init issue), > but yet without changing the number of IRQs for PIIX3, so keeping the > irq_count semantics for this host bridge. > > Now I'm facing three possibilities of how to proceed:
They all look OK I think :) Some comments below. > 1. Give up on the (currently broken) feature to write a vmstate for > older QEMU versions. > > This will allow to declare the irq_count field in vmstate_pcibus > unused, and we would have to restore it on vmload step-wise via the > PCI devices. It would also allow to change its semantics for PIIX3, > mapping directly to PIC IRQs. I think that's okay too simply because these things are usually easy to fix after the fact when the rest of the issues are addressed. > 2. Keep writing a legacy irq_count field. > > This will require quite a few new APIs so that host bridges that > want to change their nirq can still generate a compatible irq_count > vmstate field. Namely: > - A function to set up vmstate_irq_count and define a callback that > the core will invoke to prepare the vmstate_irq_count before > vmsave. > - A function to obtain the IRQ mapping /without/ the final host > bridge step. This is required so that the callback above can > calculate the old state like in the PIIX3 case. Does this really need to be so complex? It seems that we just need pci_get_irq_count(bus, irq) which can use the existing map_irq API, no? Then invoke that before save. > 3. Keep irq_count and nirq as is, introduce additional map_host_irq. > > This is simpler than 2 and more compatible than 1. It would also > allow to introduce the polarity and masking information more > smoothly as we won't have to add it to existing map_irq callbacks > then. So what does it map, and to what? Maybe we can make the name imply that somehow. > Any other suggestions? > > Jan > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux