AGENT-890: Simplify Agent ISO kargs setting

Defer to the implementation provided by assisted-image-service in
NewKargsReader(), so that we do not need to maintain any knowledge of
how kernel args are implemented in the installer.

Author: zaneb

pkg/asset/agent/image/agentartifacts.go

@@ -30,7 +30,7 @@ type AgentArtifacts struct {
 	RendezvousIP         string
 	TmpPath              string
 	IgnitionByte         []byte
-	Kargs                []byte
+	Kargs                string
 	ISOPath              string
 	BootArtifactsBaseURL string
 }

pkg/asset/agent/image/agentimage.go

@@ -8,7 +8,6 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
-	"regexp"
 
 	"github.com/sirupsen/logrus"
 
@@ -150,49 +149,16 @@ func (a *AgentImage) overwriteFileData(fileInfo []isoeditor.FileData) error {
 	return errors.Join(errs...)
 }
 
-func updateKargsFile(tmpPath, filename string, embedArea *regexp.Regexp, kargs []byte) error {
-	file, err := os.OpenFile(filepath.Join(tmpPath, filename), os.O_RDWR, 0)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-
-	content, err := io.ReadAll(file)
-	if err != nil {
-		return err
-	}
-	indices := embedArea.FindSubmatchIndex(content)
-	if len(indices) != 4 {
-		return fmt.Errorf("failed to find COREOS_KARG_EMBED_AREA in %s", filename)
-	}
-
-	if size := (indices[3] - indices[2]); len(kargs) > size {
-		return fmt.Errorf("kernel args content length (%d) exceeds embed area size (%d)", len(kargs), size)
-	}
-
-	if _, err := file.WriteAt(append(kargs, '\n'), int64(indices[2])); err != nil {
-		return err
-	}
-	return nil
-}
-
-func (a *AgentImage) appendKargs(kargs []byte) error {
-	if len(kargs) == 0 {
+func (a *AgentImage) appendKargs(kargs string) error {
+	if kargs == "" {
 		return nil
 	}
 
-	kargsFiles, err := isoeditor.KargsFiles(a.isoPath)
+	fileInfo, err := isoeditor.NewKargsReader(a.isoPath, kargs)
 	if err != nil {
 		return err
 	}
-
-	embedArea := regexp.MustCompile(`(\n#*)# COREOS_KARG_EMBED_AREA`)
-	for _, f := range kargsFiles {
-		if err := updateKargsFile(a.tmpPath, f, embedArea, kargs); err != nil {
-			return err
-		}
-	}
-	return nil
+	return a.overwriteFileData(fileInfo)
 }
 
 // normalizeFilesExtension scans the extracted ISO files and trims

pkg/asset/agent/image/kargs.go

@@ -61,10 +61,10 @@ func (a *Kargs) Name() string {
 }
 
 // KernelCmdLine returns the data to be appended to the kernel arguments.
-func (a *Kargs) KernelCmdLine() []byte {
+func (a *Kargs) KernelCmdLine() string {
 	cmdLine := a.consoleArgs
 	if a.fips {
 		cmdLine += " fips=1"
 	}
-	return []byte(cmdLine)
+	return cmdLine
 }

pkg/asset/agent/image/kargs_test.go

@@ -101,7 +101,7 @@ func TestKargs_Generate(t *testing.T) {
 
 			if tc.expectedErr == "" {
 				assert.NoError(t, err)
-				assert.Equal(t, tc.expectedArgs, string(kargs.KernelCmdLine()))
+				assert.Equal(t, tc.expectedArgs, kargs.KernelCmdLine())
 			} else {
 				assert.Regexp(t, tc.expectedErr, err.Error())
 			}