Add code for partition mounting

main.go

@@ -1,57 +1,137 @@
 package main
 
 import (
+	"encoding/binary"
+	"errors"
 	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
 	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
 )
 
 var (
-	perm = flag.String("perm", "/perm", "new val for perm")
+	perm        = flag.String("perm", "/perm", "new val for perm")
+	gloaderHome = "/perm/gloader"
 )
 
 func main() {
-	os.MkdirAll("/home/timmy/dltest", 0777)
+	flag.Parse()
+	gloaderHome = filepath.Join(*perm, "gloader")
+	os.MkdirAll(gloaderHome, 0777)
+	err := mount()
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
 	d := newDownloader()
-	d.DataDir = "/home/timmy/dltest"
-	d.Start("tcp", ":8080")
+	d.DataDir = filepath.Join(gloaderHome, "data")
+	d.Start("tcp", ":8844")
 }
 
-// func mount() error {
-// 	var (
-// 		partUUID  string
-// 		partUUIDb []byte
-// 		err       error
-// 		dataStat  os.FileInfo
-// 		dataDir   = filepath.Join(*perm, "downloader/data")
-// 	)
-// 	partUUIDb, err = ioutil.ReadFile(filepath.Join(*perm, "downloader/partition"))
-// 	if err != nil || string(partUUIDb) == "" {
-// 		return nil
-// 	}
-// 	partUUID = string(partUUIDb)
-// 	dataStat, err = os.Stat(dataDir)
-// 	if err != nil {
-// 		if errors.Is(err, os.ErrNotExist) {
-// 			err = os.MkdirAll(dataDir, 0o755)
-// 			if err != nil {
-// 				return fmt.Errorf("error creating datadir: %w", err)
-// 			}
-// 		} else {
-// 			return fmt.Errorf("error mounting datadir: %w", err)
-// 		}
-// 	}
-// 	if dataStat.IsDir() {
-// 		var folder *os.File
-// 		folder, err = os.Open(dataDir)
-// 		if err != nil {
-// 			return fmt.Errorf("error mounting datadir: %w", err)
-// 		}
-// 		_, err = folder.Readdir(1)
-// 		if errors.Is(err, io.EOF) {
-// 			fmt.Printf("mount %s %s", partUUID, dataDir)
-// 			return nil
-// 		}
-// 		return fmt.Errorf("error mounting datadir: %w", err)
-// 	}
-// 	return fmt.Errorf("error mounting datadir: data dir %s is not a directory", dataDir)
-// }
+func mount() error {
+	var (
+		partUUIDb []byte
+		partUUID  string
+		dev       string
+		err       error
+		dataStat  os.FileInfo
+		dataDir   = filepath.Join(gloaderHome, "data")
+	)
+	partUUIDb, err = ioutil.ReadFile(filepath.Join(gloaderHome, "partition"))
+	partUUID = strings.TrimSpace(string(partUUIDb))
+	if err != nil || partUUID == "" {
+		return nil
+	}
+	dataStat, err = os.Stat(dataDir)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			err = os.MkdirAll(dataDir, 0o755)
+			if err != nil {
+				return fmt.Errorf("error creating datadir: %w", err)
+			}
+			dataStat, err = os.Stat(dataDir)
+			if err != nil {
+				return fmt.Errorf("error mounting datadir: %w", err)
+			}
+		} else {
+			return fmt.Errorf("error mounting datadir: %w", err)
+		}
+	}
+	if dataStat.IsDir() {
+		var folder *os.File
+		folder, err = os.Open(dataDir)
+		if err != nil {
+			return fmt.Errorf("error mounting datadir: %w", err)
+		}
+		_, err = folder.Readdir(1)
+		if errors.Is(err, io.EOF) {
+			fmt.Printf("mount %s %s", partUUID, dataDir)
+			dev, err = findPartUUID(partUUID)
+			if err != nil {
+				return fmt.Errorf("error mounting datadir: %w", err)
+			}
+			err = syscall.Mount(dev, dataDir, "ext4", 0, "")
+			if err != nil {
+				return fmt.Errorf("error mounting datadir: %w", err)
+			}
+			return nil
+		}
+		return fmt.Errorf("error mounting datadir: %w", err)
+	}
+	return fmt.Errorf("error mounting datadir: data dir %s is not a directory", dataDir)
+}
+
+func findPartUUID(uuid string) (string, error) {
+	var dev string
+	err := filepath.Walk("/sys/block", func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			log.Printf("findPartUUID: %v", err)
+			return nil
+		}
+		if info.Mode()&os.ModeSymlink == 0 {
+			return nil
+		}
+		devname := "/dev/" + filepath.Base(path)
+		f, err := os.Open(devname)
+		if err != nil {
+			log.Printf("findPartUUID: %v", err)
+			return nil
+		}
+		defer f.Close()
+		if _, err := f.Seek(440, io.SeekStart); err != nil {
+			var se syscall.Errno
+			if errors.As(err, &se) && se == syscall.EINVAL {
+				// Seek()ing empty loop devices results in EINVAL.
+				return nil
+			}
+			log.Printf("findPartUUID: %v(%T)", err, err.(*os.PathError).Err)
+			return nil
+		}
+		var diskSig struct {
+			ID      uint32
+			Trailer uint16
+		}
+		if err := binary.Read(f, binary.LittleEndian, &diskSig); err != nil {
+			log.Printf("findPartUUID: %v", err)
+			return nil
+		}
+		if fmt.Sprintf("%08x", diskSig.ID) == uuid && diskSig.Trailer == 0 {
+			dev = devname
+			// TODO: abort early with sentinel error code
+			return nil
+		}
+		return nil
+	})
+	if err != nil {
+		return "", err
+	}
+	if dev == "" {
+		return "", fmt.Errorf("PARTUUID=%s not found", uuid)
+	}
+	return dev, nil
+}