This change introduces a new libvirt sub-element <pci> under
<features> that can be used to configure all pci related features.
Currently the only sub-sub element supported by this sub-element is
'acpi-bridge-hotplug' as shown below:
<features>
<pci>
<acpi-bridge-hotplug state='on|off'/>
</pci>
</features>
The above option is only available for the QEMU driver, for x86 guests
only. It is a global option, affecting all PCI bridge controllers on
the guest.
The 'acpi-bridge-hotplug' option enables or disables ACPI hotplug
support for cold-plugged pci bridges. Examples of bridges include the
PCI-PCI bridge (pci-bridge controller) for pc (i440fx) machinetypes,
or PCIe-PCI bridges and pcie-root-port controllers for q35
machinetypes.
For pc machinetypes in x86, this option has been available in QEMU
since version 2.1. Please see the following changes in qemu repo:
9e047b982452c6 ("piix4: add acpi pci hotplug support")
133a2da488062e ("pc: acpi: generate AML only for PCI0 devices if PCI
bridge hotplug is disabled")
For q35 machinetypes, this was introduced in QEMU 6.1 with the
following changes in qemu repo:
(a) c0e427d6eb5fef ("hw/acpi/ich9: Enable ACPI PCI hot-plug")
(b) 17858a16950860 ("hw/acpi/ich9: Set ACPI PCI hot-plug as default on
Q35")
The reasons for enabling ACPI based hotplug for PCIe (q35) based
machines (as opposed to native hotplug) are outlined in (b). There are
use cases where users would still want to use native
hotplug. Therefore, this config option enables users to choose either
ACPI based hotplug or native hotplug for bridges (for example for pcie
root port controller in q35 machines).
Qemu capability validation checks have also been added along with
related unit tests to exercise the new conf option.
Signed-off-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Laine Stump <laine@redhat.com>
