added update & uboot functions

update.go

@@ -0,0 +1,143 @@
+package alpine_builder
+
+import (
+	"compress/gzip"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"hash/crc32"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+)
+
+var ubootFile = "/uboot/uboot.dat"
+var ubootRemountRW = "mount -o remount,rw /uboot"
+var ubootRemountRO = "mount -o remount,ro /uboot"
+
+var rootPartitionA = "/dev/mmcblk0p1"
+var rootPartitionB = "/dev/mmcblk0p2"
+
+// loadUbootDat file to byte array
+func loadUbootDat() ([]byte, error) {
+	defaultData := make([]byte, 1024)
+	defaultData[0] = 1 // file version
+	defaultData[1] = 0 // boot counter
+	defaultData[2] = 1 // boot partition  A=1, B=2
+
+	data, err := ioutil.ReadFile(ubootFile)
+	if err != nil {
+		return defaultData, fmt.Errorf("failed to open file: %w", err)
+	}
+
+	// invalid dat file?
+	if len(data) < 1024 {
+		return defaultData, errors.New("invalid dat file -> fallback to defaults")
+	}
+
+	crc := binary.LittleEndian.Uint32(data[1020:])
+	bla := crc32.ChecksumIEEE(data[:1020])
+	if crc != bla {
+		return defaultData, errors.New("invalid crc -> fallback to defaults")
+	}
+
+	return data, nil
+}
+
+// saveUbootDat from byte array
+func saveUbootDat(data []byte) error {
+	// update crc
+	binary.LittleEndian.PutUint32(data[1020:],
+		crc32.ChecksumIEEE(data[:1020]))
+
+	// remount boot partition - writable
+	cmd := exec.Command(ubootRemountRW)
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("failed to remount RW: %w", err)
+	}
+
+	// update uboot dat file
+	err = ioutil.WriteFile(ubootFile, data[:1024], os.ModePerm)
+	if err != nil {
+		return fmt.Errorf("failed write uboot dat: %w", err)
+	}
+
+	// remount boot partition - readonly
+	cmd = exec.Command(ubootRemountRO)
+	err = cmd.Run()
+	if err != nil {
+		return fmt.Errorf("failed to remount RO: %w", err)
+	}
+	return nil
+}
+
+// UBootResetCounter to 0
+func UBootResetCounter() error {
+	data, _ := loadUbootDat()
+	data[1] = 0
+	return saveUbootDat(data)
+}
+
+// UBootActive returns the active partition. A=1, B=2
+func UBootActive() uint8 {
+	data, _ := loadUbootDat()
+	return data[2]
+}
+
+// UBootSetActive sets the active partition. A=1, B=2
+func UBootSetActive(active uint8) error {
+	data, _ := loadUbootDat()
+	if active == 1 {
+		data[2] = 1
+	} else {
+		data[2] = 2
+	}
+	return saveUbootDat(data)
+}
+
+// UpdateSystem with the given image
+func UpdateSystem(image string) error {
+	data, _ := loadUbootDat()
+	rootPart := rootPartitionA
+	if data[2] == 1 {
+		rootPart = rootPartitionB
+	}
+
+	// open image file
+	inFile, err := os.Open(image)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer inFile.Close()
+
+	// decompress image
+	inDecompress, err := gzip.NewReader(inFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer inDecompress.Close()
+
+	// open root partition
+	out, err := os.OpenFile(rootPart,
+		os.O_WRONLY|os.O_TRUNC|os.O_SYNC, os.ModePerm)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer out.Close()
+
+	// write update
+	_, err = io.Copy(out, inDecompress)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// switch active partition
+	if data[2] == 1 {
+		return UBootSetActive(2)
+	} else {
+		return UBootSetActive(1)
+	}
+}