metis/pkg/image/rootfs.go

package image

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"

	"metis/pkg/inject"
)

type partitionTable struct {
	PartitionTable partitionTableData `json:"partitiontable"`
}

type partitionTableData struct {
	SectorSize uint64               `json:"sectorsize"`
	Partitions []partitionTablePart `json:"partitions"`
}

type partitionTablePart struct {
	Start uint64 `json:"start"`
	Size  uint64 `json:"size"`
	Type  string `json:"type"`
}

// InjectRootFS rewrites the Linux root partition inside a raw image file without
// requiring block-device mounts. Only rootfs-targeted files are written.
func InjectRootFS(imagePath string, files []inject.FileSpec) error {
	rootFiles := make([]inject.FileSpec, 0, len(files))
	for _, f := range files {
		if f.RootFS {
			rootFiles = append(rootFiles, f)
		}
	}
	if len(rootFiles) == 0 {
		return nil
	}

	part, sectorSize, err := findLinuxPartition(imagePath)
	if err != nil {
		return err
	}

	workDir, err := os.MkdirTemp("", "metis-rootfs-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(workDir)

	rootImage := filepath.Join(workDir, "root.ext4")
	if err := extractPartition(imagePath, rootImage, part, sectorSize); err != nil {
		return err
	}
	if err := writeExt4Files(rootImage, rootFiles); err != nil {
		return err
	}
	return replacePartition(imagePath, rootImage, part, sectorSize)
}

func findLinuxPartition(imagePath string) (partitionTablePart, uint64, error) {
	out, err := exec.Command("sfdisk", "-J", imagePath).Output()
	if err != nil {
		return partitionTablePart{}, 0, fmt.Errorf("sfdisk -J %s: %w", imagePath, err)
	}
	var table partitionTable
	if err := json.Unmarshal(out, &table); err != nil {
		return partitionTablePart{}, 0, fmt.Errorf("decode partition table: %w", err)
	}
	sectorSize := table.PartitionTable.SectorSize
	if sectorSize == 0 {
		sectorSize = 512
	}
	for i := len(table.PartitionTable.Partitions) - 1; i >= 0; i-- {
		part := table.PartitionTable.Partitions[i]
		if isLinuxPartitionType(part.Type) {
			return part, sectorSize, nil
		}
	}
	return partitionTablePart{}, 0, fmt.Errorf("no Linux root partition found in %s", imagePath)
}

func isLinuxPartitionType(partType string) bool {
	normalized := strings.ToLower(strings.TrimSpace(partType))
	switch normalized {
	case "83", "8300":
		return true
	}
	return normalized == "0fc63daf-8483-4772-8e79-3d69d8477de4"
}

func extractPartition(imagePath, outPath string, part partitionTablePart, sectorSize uint64) error {
	sizeBytes := int64(part.Size * sectorSize)
	offsetBytes := int64(part.Start * sectorSize)

	src, err := os.Open(imagePath)
	if err != nil {
		return err
	}
	defer src.Close()
	if _, err := src.Seek(offsetBytes, io.SeekStart); err != nil {
		return err
	}

	out, err := os.Create(outPath)
	if err != nil {
		return err
	}
	defer out.Close()
	if _, err := io.CopyN(out, src, sizeBytes); err != nil {
		return fmt.Errorf("extract root partition: %w", err)
	}
	return out.Sync()
}

func replacePartition(imagePath, rootImage string, part partitionTablePart, sectorSize uint64) error {
	expectedSize := int64(part.Size * sectorSize)
	info, err := os.Stat(rootImage)
	if err != nil {
		return err
	}
	if info.Size() != expectedSize {
		return fmt.Errorf("root partition size mismatch: expected %d got %d", expectedSize, info.Size())
	}

	in, err := os.Open(rootImage)
	if err != nil {
		return err
	}
	defer in.Close()

	out, err := os.OpenFile(imagePath, os.O_WRONLY, 0)
	if err != nil {
		return err
	}
	defer out.Close()
	if _, err := out.Seek(int64(part.Start*sectorSize), io.SeekStart); err != nil {
		return err
	}
	if _, err := io.Copy(out, in); err != nil {
		return fmt.Errorf("write root partition: %w", err)
	}
	return out.Sync()
}

func writeExt4Files(fsPath string, files []inject.FileSpec) error {
	workDir, err := os.MkdirTemp("", "metis-ext4-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(workDir)

	stageDir := filepath.Join(workDir, "stage")
	commandFile := filepath.Join(workDir, "commands.txt")

	dirs := map[string]struct{}{}
	commands := make([]string, 0, len(files)*4)

	for _, f := range files {
		localPath := filepath.Join(stageDir, filepath.FromSlash(f.Path))
		if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
			return err
		}
		if err := os.WriteFile(localPath, f.Content, 0o644); err != nil {
			return err
		}
		for _, dir := range parentDirs(f.Path) {
			dirs[dir] = struct{}{}
		}
	}

	dirList := make([]string, 0, len(dirs))
	for dir := range dirs {
		dirList = append(dirList, dir)
	}
	sort.Slice(dirList, func(i, j int) bool {
		leftDepth := strings.Count(dirList[i], "/")
		rightDepth := strings.Count(dirList[j], "/")
		if leftDepth != rightDepth {
			return leftDepth < rightDepth
		}
		return dirList[i] < dirList[j]
	})
	for _, dir := range dirList {
		commands = append(commands, fmt.Sprintf("mkdir %s", dir))
	}

	for _, f := range files {
		destPath := "/" + strings.TrimPrefix(filepath.ToSlash(f.Path), "/")
		localPath := filepath.Join(stageDir, filepath.FromSlash(f.Path))
		commands = append(commands, fmt.Sprintf("rm %s", destPath))
		commands = append(commands, fmt.Sprintf("write %s %s", localPath, destPath))
		commands = append(commands, fmt.Sprintf("sif %s mode 0%o", destPath, uint32(0o100000|f.Mode.Perm())))
	}
	if err := os.WriteFile(commandFile, []byte(strings.Join(commands, "\n")+"\n"), 0o644); err != nil {
		return err
	}

	cmd := exec.Command("debugfs", "-w", "-f", commandFile, fsPath)
	var combined bytes.Buffer
	cmd.Stdout = &combined
	cmd.Stderr = &combined
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("debugfs write failed: %w: %s", err, combined.String())
	}

	for _, f := range files {
		if err := verifyExt4File(fsPath, f, workDir); err != nil {
			return err
		}
	}
	return nil
}

func verifyExt4File(fsPath string, file inject.FileSpec, workDir string) error {
	destPath := "/" + strings.TrimPrefix(filepath.ToSlash(file.Path), "/")
	statOut, err := exec.Command("debugfs", "-R", "stat "+destPath, fsPath).CombinedOutput()
	if err != nil {
		return fmt.Errorf("verify %s: %w: %s", destPath, err, string(statOut))
	}
	expectedMode := fmt.Sprintf("Mode:  %04o", file.Mode.Perm())
	if !strings.Contains(string(statOut), expectedMode) {
		return fmt.Errorf("verify %s mode: expected %s in %s", destPath, expectedMode, string(statOut))
	}

	readback := filepath.Join(workDir, strings.TrimPrefix(filepath.FromSlash(file.Path), string(filepath.Separator))+".readback")
	if err := os.MkdirAll(filepath.Dir(readback), 0o755); err != nil {
		return err
	}
	dumpOut, err := exec.Command("debugfs", "-R", fmt.Sprintf("dump %s %s", destPath, readback), fsPath).CombinedOutput()
	if err != nil {
		return fmt.Errorf("dump %s: %w: %s", destPath, err, string(dumpOut))
	}
	got, err := os.ReadFile(readback)
	if err != nil {
		return err
	}
	if !bytes.Equal(got, file.Content) {
		return fmt.Errorf("verify %s content mismatch", destPath)
	}
	return nil
}

func parentDirs(path string) []string {
	cleaned := "/" + strings.TrimPrefix(filepath.ToSlash(path), "/")
	parts := strings.Split(cleaned, "/")
	var dirs []string
	for i := 2; i < len(parts); i++ {
		dirs = append(dirs, strings.Join(parts[:i], "/"))
	}
	return dirs
}