fix: FC hugepages bug + io_uring + entropy + boot args tuning

- Fix hugepages: field was "hugepages" (bool), FC API needs
  "huge_pages" (string "None"/"2M"). Never worked before.
- Add io_engine "Async" (io_uring) for writable drives.
- Add PUT /entropy for virtio-rng device (parity with CH --rng).
- Add pci=off, i8042.noaux, 8250.nr_uarts=1 to kernel cmdline
  to skip unnecessary device probing (~100-200ms boot savings).

Author: CMGS

hypervisor/firecracker/api.go

@@ -31,9 +31,9 @@ const (
 // configure via HTTP PUT/PATCH, then issue InstanceStart.
 
 type fcMachineConfig struct {
-	VCPUCount  int  `json:"vcpu_count"`
-	MemSizeMiB int  `json:"mem_size_mib"`
-	HugePages  bool `json:"hugepages,omitempty"`
+	VCPUCount  int    `json:"vcpu_count"`
+	MemSizeMiB int    `json:"mem_size_mib"`
+	HugePages  string `json:"huge_pages,omitempty"` // "None" or "2M"
 }
 
 type fcBootSource struct {
@@ -47,6 +47,7 @@ type fcDrive struct {
 	PathOnHost   string `json:"path_on_host"`
 	IsRootDevice bool   `json:"is_root_device"`
 	IsReadOnly   bool   `json:"is_read_only"`
+	IoEngine     string `json:"io_engine,omitempty"` // "Sync" (default) or "Async" (io_uring)
 }
 
 type fcNetworkInterface struct {
@@ -126,6 +127,10 @@ func putNetworkInterface(ctx context.Context, hc *http.Client, iface fcNetworkIn
 	return fcAPI(ctx, hc, http.MethodPut, "/network-interfaces/"+iface.IfaceID, body)
 }
 
+func putEntropy(ctx context.Context, hc *http.Client) error {
+	return fcAPI(ctx, hc, http.MethodPut, "/entropy", []byte("{}"))
+}
+
 func instanceStart(ctx context.Context, hc *http.Client) error {
 	body, err := json.Marshal(fcAction{ActionType: actionInstanceStart})
 	if err != nil {

hypervisor/firecracker/create.go

@@ -267,8 +267,11 @@ func buildCmdline(storageConfigs []*types.StorageConfig, networkConfigs []*types
 	// FC serial console is ttyS0 (not hvc0 like CH's virtio-console).
 	// reboot=k: FC has no ACPI PM — use i8042 keyboard controller reset so
 	// guest reboot/shutdown triggers FC process exit instead of hanging.
+	// pci=off: FC has no PCI bus, skip probing (~50-100ms saved)
+	// i8042.noaux: no PS/2 mouse, skip auxiliary device probe timeout
+	// 8250.nr_uarts=1: FC exposes one serial port, skip probing for 3 others
 	fmt.Fprintf(&cmdline,
-		"console=ttyS0 reboot=k loglevel=3 boot=cocoon-overlay cocoon.layers=%s cocoon.cow=%s clocksource=kvm-clock rw",
+		"console=ttyS0 reboot=k loglevel=3 pci=off i8042.noaux 8250.nr_uarts=1 boot=cocoon-overlay cocoon.layers=%s cocoon.cow=%s clocksource=kvm-clock rw",
 		strings.Join(layerDevs, ","), cowDev,
 	)
 

hypervisor/firecracker/start.go

@@ -75,10 +75,14 @@ func (fc *Firecracker) startOne(ctx context.Context, id string) error {
 // then issues InstanceStart to boot the guest.
 func (fc *Firecracker) configureVM(ctx context.Context, hc *http.Client, rec *hypervisor.VMRecord) error {
 	memMiB := int(rec.Config.Memory >> 20) //nolint:mnd
+	hugePages := "None"
+	if utils.DetectHugePages() {
+		hugePages = "2M"
+	}
 	if err := putMachineConfig(ctx, hc, fcMachineConfig{
 		VCPUCount:  rec.Config.CPU,
 		MemSizeMiB: memMiB,
-		HugePages:  utils.DetectHugePages(),
+		HugePages:  hugePages,
 	}); err != nil {
 		return fmt.Errorf("machine-config: %w", err)
 	}
@@ -95,12 +99,16 @@ func (fc *Firecracker) configureVM(ctx context.Context, hc *http.Client, rec *hy
 
 	for i, sc := range rec.StorageConfigs {
 		driveID := fmt.Sprintf(driveIDFmt, i)
-		if err := putDrive(ctx, hc, fcDrive{
+		d := fcDrive{
 			DriveID:      driveID,
 			PathOnHost:   sc.Path,
 			IsRootDevice: false,
 			IsReadOnly:   sc.RO,
-		}); err != nil {
+		}
+		if !sc.RO {
+			d.IoEngine = "Async"
+		}
+		if err := putDrive(ctx, hc, d); err != nil {
 			return fmt.Errorf("drive %s: %w", driveID, err)
 		}
 	}
@@ -131,6 +139,10 @@ func (fc *Firecracker) configureVM(ctx context.Context, hc *http.Client, rec *hy
 		}
 	}
 
+	if err := putEntropy(ctx, hc); err != nil {
+		return fmt.Errorf("entropy: %w", err)
+	}
+
 	if err := instanceStart(ctx, hc); err != nil {
 		return fmt.Errorf("instance-start: %w", err)
 	}