add the before_start_hook

this will executed after the vm is configured, but before its started

this receives the vm configuration as a json in stdin

the hook is expected to return a json with the modified configuration

.web-docs/components/builder/clone/README.md

@@ -276,6 +276,8 @@ boot time.
   For example `-no-reboot -smbios type=0,vendor=FOO`.
   	Note: this option is for experts only.
 
+- `before_start_hook` ([]string) - Before Start Hook
+
 <!-- End of code generated from the comments of the Config struct in builder/proxmox/common/config.go; -->
 
 

.web-docs/components/builder/iso/README.md

@@ -207,6 +207,8 @@ in the image's Cloud-Init settings for provisioning.
   For example `-no-reboot -smbios type=0,vendor=FOO`.
   	Note: this option is for experts only.
 
+- `before_start_hook` ([]string) - Before Start Hook
+
 <!-- End of code generated from the comments of the Config struct in builder/proxmox/common/config.go; -->
 
 

builder/proxmox/common/config.go

@@ -196,6 +196,8 @@ type Config struct {
 	// 	Note: this option is for experts only.
 	AdditionalArgs string `mapstructure:"qemu_additional_args"`
 
+	BeforeStartHook []string `mapstructure:"before_start_hook"`
+
 	Ctx interpolate.Context `mapstructure-to-hcl2:",skip"`
 }
 

builder/proxmox/common/step_start_vm.go

@@ -4,9 +4,12 @@
 package proxmox
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
 	"fmt"
 	"log"
+	"os/exec"
 	"strconv"
 	"strings"
 
@@ -243,6 +246,65 @@ func (s *stepStartVM) Run(ctx context.Context, state multistep.StateBag) multist
 	// info available in the vmref type.
 	state.Put("instance_id", vmRef.VmId())
 
+	// Execute the before_start_hook.
+	if len(c.BeforeStartHook) > 0 {
+		ui.Say("Executing the before_start_hook")
+
+		cfg, err := client.GetVmConfig(vmRef)
+		if err != nil {
+			err := fmt.Errorf("failed to get the VM configuration: %w", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		cfgDoc, err := json.Marshal(cfg)
+		if err != nil {
+			err := fmt.Errorf("failed to marshal the VM configuration: %w", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		log.Printf("executing the before_start_hook in VM with ID %d and config %s", vmRef.VmId(), cfgDoc)
+
+		var stdout, stderr bytes.Buffer
+		cmd := exec.Command(c.BeforeStartHook[0], c.BeforeStartHook[1:]...)
+		cmd.Stdin = bytes.NewReader(cfgDoc)
+		cmd.Stdout = &stdout
+		cmd.Stderr = &stderr
+		err = cmd.Run()
+		if err != nil {
+			log.Printf("failed to execute the before_start_hook in VM with ID %d. stderr=%s stdout=%s", vmRef.VmId(), stderr.Bytes(), stdout.Bytes())
+			err := fmt.Errorf("failed to execute the before_start_hook: %w", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+		newCfgDoc := stdout.Bytes()
+
+		log.Printf("executed the before_start_hook in VM with ID %d and returned the config %s", vmRef.VmId(), newCfgDoc)
+
+		if bytes.HasPrefix(newCfgDoc, []byte{'{'}) {
+			var vmConfig map[string]interface{}
+			err = json.Unmarshal(newCfgDoc, &vmConfig)
+			if err != nil {
+				err := fmt.Errorf("failed to unmarshal the before_start_hook output: %w", err)
+				state.Put("error", err)
+				ui.Error(err.Error())
+				return multistep.ActionHalt
+			}
+
+			_, err = client.SetVmConfig(vmRef, vmConfig)
+			if err != nil {
+				err := fmt.Errorf("failed to set the VM configuration: %w", err)
+				state.Put("error", err)
+				ui.Error(err.Error())
+				return multistep.ActionHalt
+			}
+		}
+	}
+
 	ui.Say("Starting VM")
 	_, err := client.StartVm(vmRef)
 	if err != nil {

docs-partials/builder/proxmox/common/Config-not-required.mdx

@@ -139,4 +139,6 @@
   For example `-no-reboot -smbios type=0,vendor=FOO`.
   	Note: this option is for experts only.
 
+- `before_start_hook` ([]string) - Before Start Hook
+
 <!-- End of code generated from the comments of the Config struct in builder/proxmox/common/config.go; -->

docs-partials/builder/proxmox/common/hooks-not-required.mdx

@@ -0,0 +1,5 @@
+<!-- Code generated from the comments of the hooks struct in builder/proxmox/common/config.go; DO NOT EDIT MANUALLY -->
+
+- `before_start` ([]string) - Before Start
+
+<!-- End of code generated from the comments of the hooks struct in builder/proxmox/common/config.go; -->