[libvirt] [PATCH v3.5 14/18] qemu: only force an available legacy-PCI slot on domains with pci-root

[Andrea Bolognani]

On Thu, 2016-09-29 at 10:14 -0400, Laine Stump wrote:
> Andrea had the right idea when he disabled the "reserve an extra
> unused slot" bit for aarch64/virt. For *any* PCI Express-based
> machine, it is pointless since 1) an extra legacy-PCI slot can't be
> used for hotplug, since hotplug into legacy PCI slots doesn't work on
> PCI Express machinetypes, and 2) even for "coldplug" expansion,
> everybody will want to expand using Express controllers, not legacy
> PCI.
> 
> This patch eliminates the extra slot reserve unless the system has a
> pci-root (i.e. legacy PCI)

[...]
> @@ -1704,23 +1702,35 @@ qemuDomainAssignPCIAddresses(virDomainDefPtr def,
>                                                       addrs) < 0)
>              goto cleanup;
>  
> -        for (i = 0; i < addrs->nbuses; i++) {
> -            if (!qemuDomainPCIBusFullyReserved(&addrs->buses[i]))
> -                buses_reserved = false;
> -        }
> -
> -        /* Reserve 1 extra slot for a (potential) bridge only if buses
> -         * are not fully reserved yet.
> +        /* For domains that have pci-root, reserve 1 extra slot for a
> +         * (potential) bridge (for future expansion) only if buses are
> +         * not fully reserved yet (if all buses are fully reserved
> +         * with manually/previously assigned addresses, any attempt to
> +         * reserve an extra slot would fail anyway. But if all buses
> +         * are *not* fully reserved, this extra reservation might push
> +         * the config to add a new pci-bridge to plug into the final
> +         * available slot, thus preserving the ability to expand)
>           *
> -         * We don't reserve the extra slot for aarch64 mach-virt guests
> -         * either because we want to be able to have pure virtio-mmio
> -         * guests, and reserving this slot would force us to add at least
> -         * a dmi-to-pci-bridge to an otherwise PCI-free topology
> +         * We only do this for those domains that have pci-root, since
> +         * those with pcie-root will usually want to expand using PCIe
> +         * controllers, which we will do after assigning addresses for
> +         * all *actual* devices.
>           */
> -        if (!buses_reserved &&
> -            !qemuDomainMachineIsVirt(def) &&
> -            qemuDomainPCIAddressReserveNextSlot(addrs, &info) < 0)
> -            goto cleanup;
> +
> +        if (qemuDomainMachineHasPCIRoot(def)) {

Since now you're using info exclusively inside this block,
you can move its declaration here as well.

ACK

-- 
Andrea Bolognani / Red Hat / Virtualization