This change introduces libvirt xml support to enable/disable hotplug on the
pci-root controller. It adds a 'target' subelement for the pci-root controller
with a 'hotplug' property. This property can be used to enable or disable
hotplug for the pci-root controller. For example, in order to disable hotplug
on the pci-root controller, one has to use set '<target hotplug='off'>' as
shown below:

<controller type='pci' model='pci-root'>
  <target hotplug='off'/>
</controller>

'<target hotplug='on'>' option would enable hotplug for pci-root controller.
This is also the default value. This option is only available for pc machine
types and is applicable for qemu/kvm accelerator only.This feature was
introduced from qemu version 5.2 with the following change in qemu repository:

3d7e78aa7777f ("Introduce a new flag for i440fx to disable PCI hotplug on the 
root bus")

The above qemu commit describes some reasons why users might to disable hotplug
on PCI root buses.

Related unit tests to exercise the new conf option has also been added.

Signed-off-by: Ani Sinha <a...@anisinha.ca>
Reviewed-by: Daniel P. Berrangé <berra...@redhat.com>
---
 docs/formatdomain.rst                         | 14 +++++----
 src/qemu/qemu_validate.c                      |  9 +++++-
 .../pc-i440fx-acpi-root-hotplug-disable.xml   | 30 +++++++++++++++++++
 .../pc-i440fx-acpi-root-hotplug-enable.xml    | 30 +++++++++++++++++++
 .../pc-i440fx-acpi-root-hotplug-disable.xml   |  1 +
 .../pc-i440fx-acpi-root-hotplug-enable.xml    |  1 +
 tests/qemuxml2xmltest.c                       |  4 +++
 7 files changed, 83 insertions(+), 6 deletions(-)
 create mode 100644 
tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml
 create mode 100644 
tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml
 create mode 120000 
tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-disable.xml
 create mode 120000 
tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-enable.xml

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 0f5d833521..467213cc29 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -3776,11 +3776,15 @@ generated by libvirt. :since:`Since 1.2.19 (QEMU only).`
    controller's "port" configuration value, which is visible to the virtual
    machine. If set, port must be between 0 and 255.
 ``hotplug``
-   pcie-root-port and pcie-switch-downstream-port controllers can also have a
-   ``hotplug`` attribute in the ``<target>`` subelement, which is used to
-   disable hotplug/unplug of devices on a particular controller. The default
-   setting of ``hotplug`` is ``on``; it should be set to ``off`` to disable
-   hotplug/unplug of devices on a particular controller. :since:`Since 6.3.0`
+   pci-root (:since:`Since 7.9.0`), pcie-root-port (:since:`Since 6.3.0`) and
+   pcie-switch-downstream-port controllers (:since:`Since 6.3.0`) can
+   also have a ``hotplug`` attribute in the ``<target>`` subelement, which is
+   used to disable hotplug/unplug of devices on a particular controller. For
+   the pci-root controller, the setting affects the ACPI based hotplug. For the
+   rest, the setting affects both ACPI based hotplug as well as PCIE native
+   hotplug. The default setting of ``hotplug`` is ``on``; it should be set to
+   ``off`` to disable hotplug/unplug of devices on a particular controller.
+
 ``busNr``
    pci-expander-bus and pcie-expander-bus controllers can have an optional
    ``busNr`` attribute (1-254). This will be the bus number of the new bus; All
diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index 294cc24b36..d7e306e29d 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -3872,6 +3872,14 @@ qemuValidateDomainDeviceDefControllerPCI(const 
virDomainControllerDef *cont,
     /* hotplug */
     if (pciopts->hotplug != VIR_TRISTATE_SWITCH_ABSENT) {
         switch ((virDomainControllerModelPCI) cont->model) {
+        case VIR_DOMAIN_CONTROLLER_MODEL_PCI_ROOT:
+            if (!virQEMUCapsGet(qemuCaps, 
QEMU_CAPS_PIIX_ACPI_ROOT_PCI_HOTPLUG)) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("setting the %s property on a '%s' device is 
not supported by this QEMU binary"),
+                               "hotplug", "pci-root");
+                return -1;
+            }
+            break;
         case VIR_DOMAIN_CONTROLLER_MODEL_PCIE_ROOT_PORT:
         case VIR_DOMAIN_CONTROLLER_MODEL_PCIE_SWITCH_DOWNSTREAM_PORT:
             if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCIE_ROOT_PORT_HOTPLUG)) {
@@ -3882,7 +3890,6 @@ qemuValidateDomainDeviceDefControllerPCI(const 
virDomainControllerDef *cont,
             }
             break;
 
-        case VIR_DOMAIN_CONTROLLER_MODEL_PCI_ROOT:
         case VIR_DOMAIN_CONTROLLER_MODEL_PCI_BRIDGE:
         case VIR_DOMAIN_CONTROLLER_MODEL_DMI_TO_PCI_BRIDGE:
         case VIR_DOMAIN_CONTROLLER_MODEL_PCIE_SWITCH_UPSTREAM_PORT:
diff --git a/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml 
b/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml
new file mode 100644
index 0000000000..93f2779f68
--- /dev/null
+++ b/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml
@@ -0,0 +1,30 @@
+<domain type='qemu'>
+  <name>i440fx</name>
+  <uuid>56f5055c-1b8d-490c-844a-ad646a1caaaa</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc-i440fx-2.5'>hvm</type>
+    <boot dev='network'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' index='0' model='pci-root'>
+      <target hotplug='off'/>
+    </controller>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x2'/>
+    </controller>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <audio id='1' type='none'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' 
function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml 
b/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml
new file mode 100644
index 0000000000..7c9241958c
--- /dev/null
+++ b/tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml
@@ -0,0 +1,30 @@
+<domain type='qemu'>
+  <name>i440fx</name>
+  <uuid>56f5055c-1b8d-490c-844a-ad646a1caaaa</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc-i440fx-2.5'>hvm</type>
+    <boot dev='network'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' index='0' model='pci-root'>
+      <target hotplug='on'/>
+    </controller>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x2'/>
+    </controller>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <audio id='1' type='none'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' 
function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-disable.xml 
b/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-disable.xml
new file mode 120000
index 0000000000..0570e40273
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-disable.xml
@@ -0,0 +1 @@
+../qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml
\ No newline at end of file
diff --git a/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-enable.xml 
b/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-enable.xml
new file mode 120000
index 0000000000..2b0e42925f
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-enable.xml
@@ -0,0 +1 @@
+../qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml
\ No newline at end of file
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 49b291fadb..eb638c112d 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -424,6 +424,10 @@ mymain(void)
     DO_TEST_NOCAPS("input-usbtablet");
     DO_TEST_NOCAPS("misc-acpi");
     DO_TEST("misc-disable-s3", QEMU_CAPS_PIIX_DISABLE_S3);
+    DO_TEST("pc-i440fx-acpi-root-hotplug-disable",
+            QEMU_CAPS_PIIX_ACPI_ROOT_PCI_HOTPLUG);
+    DO_TEST("pc-i440fx-acpi-root-hotplug-enable",
+            QEMU_CAPS_PIIX_ACPI_ROOT_PCI_HOTPLUG);
     DO_TEST("misc-disable-suspends",
             QEMU_CAPS_PIIX_DISABLE_S3,
             QEMU_CAPS_PIIX_DISABLE_S4);
-- 
2.25.1

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