runtime-rs: Add pci_hotplug as a config option

There are cases where enabling PCI hotplug by default, breaks
Dragonball's initial setup [see kata-containers#9596], resulting in the following
error message:

```
FATA[0000] failed to create shim task: Others("failed to handle message try
init runtime instance\n\nCaused by:\n    0: init runtime handler\n
1: start sandbox\n    2: start vm\n  3: start vmm instance\n
4: Failed to start vmm\n    5: Failed to start MicroVm\n
6: vmm action error: StartMicroVm(CreateVfioDevice(NoResource))"): unknown
```

Adding this as a config option enables normal booting even on nodes that
lack the default functionality.

Fixes: kata-containers#9509

Signed-off-by: Anastassios Nanos <ananos@nubificus.co.uk>

src/libs/kata-types/src/config/hypervisor/mod.rs

@@ -447,6 +447,14 @@ pub struct DeviceInfo {
     #[serde(default)]
     pub default_bridges: u32,
 
+    /// Enable PCI hotplug support, default false
+    ///
+    /// This is a Dragonball only config for the time being.
+    ///
+    /// Enabling this will result in hotplugin VFIO devices (see below).
+    #[serde(default)]
+    pub pci_hotplug: bool,
+
     /// VFIO devices are hotplugged on a bridge by default.
     ///
     /// Enable hotplugging on root bus. This may be required for devices with a large PCI bar,

src/runtime-rs/Makefile

@@ -130,6 +130,7 @@ DEFMEMSLOTS := 10
 DEFMAXMEMSZ := 0
 ##VAR DEFBRIDGES=<number> Default number of bridges
 DEFBRIDGES := 0
+DEFPCIHOTPLUG := false
 DEFENABLEANNOTATIONS := [\"kernel_params\"]
 DEFDISABLEGUESTSECCOMP := true
 DEFDISABLEGUESTEMPTYDIR := false
@@ -362,6 +363,7 @@ USER_VARS += DEFMEMSZ
 USER_VARS += DEFMEMSLOTS
 USER_VARS += DEFMAXMEMSZ
 USER_VARS += DEFBRIDGES
+USER_VARS += DEFPCIHOTPLUG
 USER_VARS += DEFNETWORKMODEL_DB
 USER_VARS += DEFNETWORKMODEL_CLH
 USER_VARS += DEFNETWORKMODEL_QEMU

src/runtime-rs/config/configuration-dragonball.toml.in

@@ -97,6 +97,12 @@ default_maxvcpus = @DEFMAXVCPUS_DB@
 # > 5                --> will be set to 5
 default_bridges = @DEFBRIDGES@
 
+# PCI hotplug
+# Enable or disable pci_hotplug
+# Only available on Dragonball for the time being.
+# Default value: @DEFPCIHOTPLUG@
+pci_hotplug = @DEFPCIHOTPLUG@
+
 # Default memory size in MiB for SB/VM.
 # If unspecified then it will be set @DEFMEMSZ@ MiB.
 default_memory = @DEFMEMSZ@

src/runtime-rs/crates/hypervisor/src/dragonball/inner.rs

@@ -220,7 +220,7 @@ impl DragonballInner {
             max_vcpu_count: self.config.cpu_info.default_maxvcpus as u8,
             mem_type,
             mem_file_path,
-            pci_hotplug_enabled: true,
+            pci_hotplug_enabled: self.hypervisor_config().device_info.pci_hotplug,
             ..Default::default()
         };
         info!(sl!(), "vm config: {:?}", vm_config);