kexec: support multiple initrd files via concatenation

kexec/cmd/grub/grub.go

@@ -9,7 +9,7 @@ import (
 type Config struct {
 	Name          string   `json:"name,omitempty"`
 	Kernel        string   `json:"kernel"`
-	Initramfs     string   `json:"initramfs,omitempty"`
+	Initramfs     []string `json:"initramfs,omitempty"`
 	KernelArgs    string   `json:"kernel_args,omitempty"`
 	Multiboot     string   `json:"multiboot_kernel,omitempty"`
 	MultibootArgs string   `json:"multiboot_args,omitempty"`
@@ -53,7 +53,7 @@ func ParseGrubCfg(grubcfg string) (configs []Config, defaultConfig int64) {
 			// if a "menuentry", start a new boot config
 			if cfg != nil {
 				// save the previous boot config, if any
-				if cfg.Kernel != "" && cfg.Initramfs != "" {
+				if cfg.Kernel != "" && len(cfg.Initramfs) > 0 {
 					// only consider valid boot configs, i.e. the ones that have
 					// both kernel and initramfs
 					configs = append(configs, *cfg)
@@ -84,8 +84,7 @@ func ParseGrubCfg(grubcfg string) (configs []Config, defaultConfig int64) {
 				cfg.Kernel = kernel
 				cfg.KernelArgs = cmdline
 			case "initrd", "initrd16", "initrdefi":
-				initrd := sline[1]
-				cfg.Initramfs = initrd
+				cfg.Initramfs = sline[1:]
 			case "multiboot", "multiboot2":
 				multiboot := sline[1]
 				cmdline := strings.Join(sline[2:], " ")
@@ -106,7 +105,7 @@ func ParseGrubCfg(grubcfg string) (configs []Config, defaultConfig int64) {
 	}
 
 	// append last kernel config if it wasn't already
-	if inMenuEntry && cfg.Kernel != "" && cfg.Initramfs != "" {
+	if inMenuEntry && cfg.Kernel != "" && len(cfg.Initramfs) > 0 {
 		configs = append(configs, *cfg)
 	}
 	return configs, defaultConfig

kexec/cmd/grub/grub_test.go

@@ -5,6 +5,13 @@ import (
 	"testing"
 )
 
+var multiInitrdConfig = `
+menuentry 'Ubuntu' --class ubuntu --class gnu-linux {
+        linux   /boot/vmlinuz-6.8.0-51-generic root=/dev/sda2 ro quiet
+        initrd  /boot/amd64-microcode.img /boot/initrd.img-6.8.0-51-generic
+}
+`
+
 var workingConfig = `#
 # DO NOT EDIT THIS FILE
 #
@@ -387,13 +394,26 @@ func TestGetDefaultCconfig(t *testing.T) {
 			&Config{
 				"'Ubuntu' ",
 				"/boot/vmlinuz-4.15.0-135-generic",
-				"/boot/initrd.img-4.15.0-135-generic",
+				[]string{"/boot/initrd.img-4.15.0-135-generic"},
 				"root=/dev/mapper/code--vg-root ro",
 				"",
 				"",
 				nil,
 			},
 		},
+		{
+			"multi-initrd",
+			args{multiInitrdConfig},
+			&Config{
+				"'Ubuntu' ",
+				"/boot/vmlinuz-6.8.0-51-generic",
+				[]string{"/boot/amd64-microcode.img", "/boot/initrd.img-6.8.0-51-generic"},
+				"root=/dev/sda2 ro quiet",
+				"",
+				"",
+				nil,
+			},
+		},
 	}
 	// Should determine our "default configuration"
 	for _, tt := range tests {

kexec/cmd/kexec.go

@@ -2,7 +2,7 @@ package cmd
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"path/filepath"
 	"syscall"
@@ -33,8 +33,8 @@ var kexecCmd = &cobra.Command{
 		cmdLine := os.Getenv("CMD_LINE")
 		grubCfgPath := os.Getenv("GRUBCFG_PATH")		
 
-		// These two strings contain the updated paths including the mountAction path
-		var kernelMountPath, initrdMountPath string
+		var kernelMountPath string
+		var initrdMountPaths []string
 
 		if blockDevice == "" {
 			log.Fatalf("No Block Device speified with Environment Variable [BLOCK_DEVICE]")
@@ -60,7 +60,7 @@ var kexecCmd = &cobra.Command{
 		// If we specify no kernelPath then we will fallback to autodetect and ignore the initrd and cmdline that may be passed
 		// by environment variables
 		if kernelPath == "" {
-			grubFile, err := ioutil.ReadFile(fmt.Sprintf("%s/%s", mountAction, grubCfgPath))
+			grubFile, err := os.ReadFile(fmt.Sprintf("%s/%s", mountAction, grubCfgPath))
 			if err != nil {
 				log.Fatal(err)
 			}
@@ -70,27 +70,30 @@ var kexecCmd = &cobra.Command{
 			}
 			log.Infof("Loaded boot config: %#v", bootConfig)
 			kernelMountPath = filepath.Join(mountAction, bootConfig.Kernel)
-			initrdMountPath = filepath.Join(mountAction, bootConfig.Initramfs)
+			for _, p := range bootConfig.Initramfs {
+				initrdMountPaths = append(initrdMountPaths, filepath.Join(mountAction, p))
+			}
 			// Overwrite the cmdline with what is found in grub.conf, unless something specific is added
 			if cmdLine == "" {
 				cmdLine = bootConfig.KernelArgs
 			}
 		} else {
 			kernelMountPath = filepath.Join(mountAction, kernelPath)
-			initrdMountPath = filepath.Join(mountAction, initrdPath)
+			initrdMountPaths = []string{filepath.Join(mountAction, initrdPath)}
 		}
-		// /mountAction/boot/vmlinuz
-		kernel, err := os.Open(kernelMountPath) // For read access.
+
+		kernel, err := os.Open(kernelMountPath)
 		if err != nil {
 			log.Fatal(err)
 		}
-		// /mountAction/boot/vmlinuz
-		initrd, err := os.Open(initrdMountPath) // For read access.
+
+		initrd, err := openInitrd(initrdMountPaths)
 		if err != nil {
 			log.Fatal(err)
 		}
+		defer os.Remove(initrd.Name())
 
-		log.Infof("Running Kexec: kernel: %s, initrd: %s, cmdLine: %v", kernelMountPath, initrdMountPath, cmdLine)
+		log.Infof("Running Kexec: kernel: %s, initrd: %v, cmdLine: %v", kernelMountPath, initrdMountPaths, cmdLine)
 		// Load the kernel configuration into memory
 		err = unix.KexecFileLoad(int(kernel.Fd()), int(initrd.Fd()), cmdLine, 0)
 		if err != nil {
@@ -109,3 +112,38 @@ func Execute() {
 		os.Exit(1)
 	}
 }
+
+// openInitrd returns a file ready for KexecFileLoad. For a single initrd it
+// opens the file directly; for multiple initrds it concatenates them into a
+// temp file (the Linux kernel accepts concatenated cpio archives).
+func openInitrd(paths []string) (*os.File, error) {
+	if len(paths) == 1 {
+		return os.Open(paths[0])
+	}
+	if err := os.MkdirAll("/tmp", 0755); err != nil {
+		return nil, fmt.Errorf("creating /tmp: %w", err)
+	}
+	tmp, err := os.CreateTemp("/tmp", "initrd-*")
+	if err != nil {
+		return nil, fmt.Errorf("creating temp initrd: %w", err)
+	}
+	for _, p := range paths {
+		f, err := os.Open(p)
+		if err != nil {
+			tmp.Close()
+			os.Remove(tmp.Name())
+			return nil, fmt.Errorf("opening initrd %s: %w", p, err)
+		}
+		_, err = io.Copy(tmp, f)
+		f.Close()
+		if err != nil {
+			tmp.Close()
+			os.Remove(tmp.Name())
+			return nil, fmt.Errorf("copying initrd %s: %w", p, err)
+		}
+	}
+	name := tmp.Name()
+	tmp.Close()
+	// Reopen read-only — KexecFileLoad rejects files with writable fds open (ETXTBSY).
+	return os.Open(name)
+}