feat(initramfs): API for creating new partition tables (#227)

src/initramfs/pkg/blockdevice/blockdevice.go

@@ -2,11 +2,14 @@
 package blockdevice
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 
 	"github.com/autonomy/talos/src/initramfs/pkg/blockdevice/table"
 	"github.com/autonomy/talos/src/initramfs/pkg/blockdevice/table/gpt"
+	"github.com/pkg/errors"
+
 	"golang.org/x/sys/unix"
 )
 
@@ -18,18 +21,41 @@ type BlockDevice struct {
 }
 
 // Open initializes and returns a block device.
-func Open(devname string) (*BlockDevice, error) {
+// TODO(andrewrynhard): Use BLKGETSIZE ioctl to get the size.
+// TODO(andrewrynhard): Use BLKPBSZGET ioctl to get the physical sector size.
+// TODO(andrewrynhard): Use BLKSSZGET ioctl to get the logical sector size
+// and pass them into gpt as options.
+func Open(devname string, setters ...Option) (*BlockDevice, error) {
+	opts := NewDefaultOptions(setters...)
+
+	bd := &BlockDevice{}
+
 	f, err := os.OpenFile(devname, os.O_RDWR, os.ModeDevice)
 	if err != nil {
 		return nil, err
 	}
-	// TODO: Dynamically detect MBR/GPT.
-	// TODO: Use BLKGETSIZE ioctl to get the size.
-	// TODO: Use BLKPBSZGET ioctl to get the physical sector size.
-	// TODO: Use BLKSSZGET ioctl to get the logical sector size.
-	// and pass them into gpt as options.
-	bd := &BlockDevice{
-		table: gpt.NewGPT(devname, f),
+
+	if opts.CreateGPT {
+		gpt := gpt.NewGPT(devname, f)
+		table, e := gpt.New()
+		if e != nil {
+			return nil, e
+		}
+		bd.table = table
+	} else {
+		buf := make([]byte, 1)
+		// PMBR protective entry starts at 446. The partition type is at offset
+		// 4 from the start of the PMBR protective entry.
+		_, err = f.ReadAt(buf, 450)
+		if err != nil {
+			return nil, err
+		}
+		// For GPT, the partition type should be 0xee (EFI GPT).
+		if bytes.Equal(buf, []byte{0xee}) {
+			bd.table = gpt.NewGPT(devname, f)
+		} else {
+			return nil, errors.New("failed to find GUID partition table")
+		}
 	}
 
 	return bd, nil
@@ -46,10 +72,10 @@ func (bd *BlockDevice) PartitionTable() (table.PartitionTable, error) {
 		return nil, fmt.Errorf("missing partition table")
 	}
 
-	return bd.table, nil
+	return bd.table, bd.table.Read()
 }
 
-// RereadPartitionTable invokes the BLKRRPART ioctl have the kernel read the
+// RereadPartitionTable invokes the BLKRRPART ioctl to have the kernel read the
 // partition table.
 func (bd *BlockDevice) RereadPartitionTable(devname string) error {
 	f, err := os.Open(devname)

src/initramfs/pkg/blockdevice/bockdevice_options.go

@@ -0,0 +1,29 @@
+package blockdevice
+
+// Options is the functional options struct.
+type Options struct {
+	CreateGPT bool
+}
+
+// Option is the functional option func.
+type Option func(*Options)
+
+// WithNewGPT opens the blockdevice with a new GPT.
+func WithNewGPT(o bool) Option {
+	return func(args *Options) {
+		args.CreateGPT = o
+	}
+}
+
+// NewDefaultOptions initializes a Options struct with default values.
+func NewDefaultOptions(setters ...Option) *Options {
+	opts := &Options{
+		CreateGPT: false,
+	}
+
+	for _, setter := range setters {
+		setter(opts)
+	}
+
+	return opts
+}

src/initramfs/pkg/blockdevice/table/gpt/gpt.go

@@ -2,6 +2,7 @@
 package gpt
 
 import (
+	"encoding/binary"
 	"fmt"
 	"os"
 	"syscall"
@@ -13,6 +14,7 @@ import (
 	"github.com/autonomy/talos/src/initramfs/pkg/blockdevice/table/gpt/header"
 	"github.com/autonomy/talos/src/initramfs/pkg/blockdevice/table/gpt/partition"
 	"github.com/google/uuid"
+	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
 )
 
@@ -105,6 +107,90 @@ func (gpt *GPT) Write() error {
 	return gpt.Read()
 }
 
+// New creates a new partition table and writes it to disk.
+func (gpt *GPT) New() (table.PartitionTable, error) {
+	// Seek to the end to get the size.
+	size, err := gpt.f.Seek(0, 2)
+	if err != nil {
+		return nil, err
+	}
+	// Reset and seek to the beginning.
+	_, err = gpt.f.Seek(0, 0)
+	if err != nil {
+		return nil, err
+	}
+
+	h, err := gpt.newHeader(size)
+	if err != nil {
+		return nil, err
+	}
+	pmbr, err := gpt.newPMBR(h)
+	if err != nil {
+		return nil, err
+	}
+
+	gpt.header = h
+	gpt.partitions = []table.Partition{}
+
+	written, err := gpt.f.WriteAt(pmbr[446:], 446)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to write the protective MBR")
+	}
+	if written != len(pmbr[446:]) {
+		return nil, errors.Errorf("expected a write %d bytes, got %d", written, len(pmbr[446:]))
+	}
+
+	if err := gpt.Write(); err != nil {
+		return nil, err
+	}
+
+	return gpt, nil
+}
+
+func (gpt *GPT) newHeader(size int64) (*header.Header, error) {
+	h := &header.Header{}
+	h.Signature = "EFI PART"
+	h.Revision = binary.LittleEndian.Uint32([]byte{0x00, 0x00, 0x01, 0x00})
+	h.Size = header.HeaderSize
+	h.Reserved = binary.LittleEndian.Uint32([]byte{0x00, 0x00, 0x00, 0x00})
+	h.CurrentLBA = 1
+	h.BackupLBA = uint64(size/int64(gpt.lba.PhysicalBlockSize) - 1)
+	h.FirstUsableLBA = 34
+	h.LastUsableLBA = h.BackupLBA - 33
+	guuid, err := uuid.NewUUID()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to generate UUID for new partition table")
+	}
+	h.GUUID = guuid
+	h.PartitionEntriesStartLBA = 2
+	h.NumberOfPartitionEntries = 128
+	h.PartitionEntrySize = 128
+
+	return h, nil
+}
+
+// See:
+// - https://en.wikipedia.org/wiki/GUID_Partition_Table#Protective_MBR_(LBA_0)
+// - https://www.syslinux.org/wiki/index.php?title=Doc/gpt
+// - https://en.wikipedia.org/wiki/Master_boot_record
+func (gpt *GPT) newPMBR(h *header.Header) ([]byte, error) {
+	pmbr := make([]byte, 512)
+
+	// Boot signature.
+	copy(pmbr[510:], []byte{0x55, 0xaa})
+	// PMBR protective entry.
+	b := pmbr[446 : 446+16]
+	b[0] = 0x00
+	// Partition type: EFI data partition.
+	b[4] = 0xee
+	// Partition start LBA.
+	binary.LittleEndian.PutUint32(b[8:12], 1)
+	// Partition length in sectors.
+	binary.LittleEndian.PutUint32(b[12:16], uint32(h.BackupLBA))
+
+	return pmbr, nil
+}
+
 // Write the primary table.
 func (gpt *GPT) writePrimary(partitions []byte) error {
 	header, err := gpt.deserializeHeader(partitions)
@@ -187,7 +273,7 @@ func (gpt *GPT) Add(size uint64, setters ...interface{}) (table.Partition, error
 	end = start + size/uint64(gpt.PhysicalBlockSize())
 
 	if end > gpt.header.LastUsableLBA {
-		// TODO: This calculation is wrong, fix it.
+		// TODO(andrewrynhard): This calculation is wrong, fix it.
 		available := (gpt.header.LastUsableLBA - start) * uint64(gpt.PhysicalBlockSize())
 		return nil, fmt.Errorf("requested partition size %d is too big, largest available is %d", size, available)
 	}
@@ -202,7 +288,7 @@ func (gpt *GPT) Add(size uint64, setters ...interface{}) (table.Partition, error
 		ID:       uuid,
 		FirstLBA: start,
 		LastLBA:  end,
-		// TODO: Flags should be an option.
+		// TODO(andrewrynhard): Flags should be an option.
 		Flags:  0,
 		Name:   opts.Name,
 		Number: int32(len(gpt.partitions) + 1),
@@ -222,14 +308,14 @@ func (gpt *GPT) Add(size uint64, setters ...interface{}) (table.Partition, error
 }
 
 // Resize resizes a partition.
-// TODO: Verify that we can indeed grow this partition safely.
+// TODO(andrewrynhard): Verify that we can indeed grow this partition safely.
 func (gpt *GPT) Resize(p table.Partition) error {
 	partition, ok := p.(*partition.Partition)
 	if !ok {
 		return fmt.Errorf("partition is not a GUID partition table partition")
 	}
 
-	// TODO: This should be a parameter.
+	// TODO(andrewrynhard): This should be a parameter.
 	partition.LastLBA = gpt.header.LastUsableLBA
 
 	index := partition.Number - 1
@@ -256,7 +342,6 @@ func (gpt *GPT) PhysicalBlockSize() int {
 	return gpt.lba.PhysicalBlockSize
 }
 
-// TODO: Rename this func, it doesn't deserialize anything.
 func (gpt *GPT) readPrimary() ([]byte, error) {
 	// LBA 34 is the first usable sector on the disk.
 	table := gpt.lba.Make(34)
@@ -338,7 +423,7 @@ func (gpt *GPT) serializePartitions(header *header.Header) ([]table.Partition, e
 }
 
 func (gpt *GPT) deserializePartitions() ([]byte, error) {
-	// TODO: Should this be a method on the Header struct?
+	// TODO(andrewrynhard): Should this be a method on the Header struct?
 	data := make([]byte, gpt.header.NumberOfPartitionEntries*gpt.header.PartitionEntrySize)
 
 	for j, p := range gpt.partitions {

src/initramfs/pkg/blockdevice/table/table.go

@@ -22,6 +22,8 @@ type PartitionTable interface {
 	Partitions() []Partition
 	// Repair repairs a partition table.
 	Repair() error
+	// New creates a new partition table.
+	New() (PartitionTable, error)
 	// Partitioner must be implemented by a partition table.
 	Partitioner
 }