move to pkg/btrfs, get CRC working

4 files changed, 238 insertions, 0 deletions

diff --git a/pkg/btrfs/crc32c.go b/pkg/btrfs/crc32c.go
new file mode 100644
index 0000000..4ea4169
--- /dev/null
+++ b/pkg/btrfs/crc32c.go
@@ -0,0 +1,16 @@
+package btrfs
+
+import (
+	"encoding/binary"
+	"hash/crc32"
+)
+
+type CSum [0x20]byte
+
+func CRC32c(data []byte) CSum {
+	crc := crc32.Update(0, crc32.MakeTable(crc32.Castagnoli), data)
+
+	var ret CSum
+	binary.LittleEndian.PutUint32(ret[:], crc)
+	return ret
+}
diff --git a/pkg/btrfs/image.go b/pkg/btrfs/image.go
new file mode 100644
index 0000000..6037c4d
--- /dev/null
+++ b/pkg/btrfs/image.go
@@ -0,0 +1,71 @@
+package btrfs
+
+import (
+	"fmt"
+	"os"
+
+	"lukeshu.com/btrfs-tools/pkg/binstruct"
+)
+
+type Img struct {
+	*os.File
+}
+
+func (img *Img) Size() (int64, error) {
+	fi, err := img.Stat()
+	if err != nil {
+		return 0, err
+	}
+	return fi.Size(), nil
+}
+
+type Ref[T any] struct {
+	img  *Img
+	addr int64
+	Data T
+}
+
+func (r *Ref[T]) Read() error {
+	size, err := binstruct.Size(r.Data)
+	if err != nil {
+		return err
+	}
+	buf := make([]byte, size)
+	if _, err := r.img.ReadAt(buf, r.addr); err != nil {
+		return err
+	}
+	return binstruct.Unmarshal(buf, &r.Data)
+}
+
+func (img *Img) Superblocks() ([]Ref[Superblock], error) {
+	const superblockSize = 0x1000
+
+	var superblockAddrs = []int64{
+		0x00_0001_0000, // 64KiB
+		0x00_0400_0000, // 64MiB
+		0x40_0000_0000, // 256GiB
+	}
+
+	sz, err := img.Size()
+	if err != nil {
+		return nil, err
+	}
+
+	var ret []Ref[Superblock]
+	for i, addr := range superblockAddrs {
+		if addr+superblockSize <= sz {
+			superblock := Ref[Superblock]{
+				img:  img,
+				addr: addr,
+			}
+			if err := superblock.Read(); err != nil {
+				return nil, fmt.Errorf("superblock %d: %w", i, err)
+			}
+			ret = append(ret, superblock)
+		}
+	}
+	if len(ret) == 0 {
+		return nil, fmt.Errorf("no superblocks")
+	}
+	return ret, nil
+}
diff --git a/pkg/btrfs/types.go b/pkg/btrfs/types.go
new file mode 100644
index 0000000..2949a8b
--- /dev/null
+++ b/pkg/btrfs/types.go
@@ -0,0 +1,132 @@
+package btrfs
+
+import (
+	"time"
+
+	"lukeshu.com/btrfs-tools/pkg/binstruct"
+)
+
+type (
+	PhysicalAddr int64
+	LogicalAddr  int64
+	ObjID        int64
+)
+
+type Key struct {
+	ObjectID      ObjID  `bin:"off=0, siz=8, desc=Object ID. Each tree has its own set of Object IDs."`
+	ItemType      uint8  `bin:"off=8, siz=1, desc=Item type."`
+	Offset        uint64 `bin:"off=9, siz=8, desc=Offset. The meaning depends on the item type."`
+	binstruct.End `bin:"off=11"`
+}
+
+type Time struct {
+	Sec           int64  `bin:"off=0, siz=8, desc=Number of seconds since 1970-01-01T00:00:00Z."`
+	NSec          uint64 `bin:"off=8, siz=4, desc=Number of nanoseconds since the beginning of the second."`
+	binstruct.End `bin:"off=c"`
+}
+
+func (t Time) ToStd() time.Time {
+	return time.Unix(t.Sec, int64(t.NSec))
+}
+
+type Superblock struct {
+	Checksum   CSum         `bin:"off=0,  siz=20, desc=Checksum of everything past this field (from 20 to 1000)"`
+	FSUUID     UUID         `bin:"off=20, siz=10, desc=FS UUID"`
+	Self       PhysicalAddr `bin:"off=30, siz=8,  desc=physical address of this block (different for mirrors)"`
+	Flags      uint64       `bin:"off=38, siz=8,  desc=flags"`
+	Magic      [8]byte      `bin:"off=40, siz=8,  desc=magic ('_BHRfS_M')"`
+	Generation uint64       `bin:"off=48, siz=8,  desc=generation"`
+
+	RootTree  LogicalAddr `bin:"off=50, siz=8,  desc=logical address of the root tree root"`
+	ChunkTree LogicalAddr `bin:"off=58, siz=8,  desc=logical address of the chunk tree root"`
+	LogTree   LogicalAddr `bin:"off=60, siz=8,  desc=logical address of the log tree root"`
+
+	LogRootTransID  uint64 `bin:"off=68, siz=8, desc=log_root_transid"`
+	TotalBytes      uint64 `bin:"off=70, siz=8, desc=total_bytes"`
+	BytesUsed       uint64 `bin:"off=78, siz=8, desc=bytes_used"`
+	RootDirObjectID uint64 `bin:"off=80, siz=8, desc=root_dir_objectid (usually 6)"`
+	NumDevices      uint64 `bin:"off=88, siz=8, desc=num_devices"`
+
+	SectorSize        uint32 `bin:"off=90, siz=4, desc=sectorsize"`
+	NodeSize          uint32 `bin:"off=94, siz=4, desc=nodesize"`
+	LeafSize          uint32 `bin:"off=98, siz=4, desc=leafsize"`
+	StripeSize        uint32 `bin:"off=9c, siz=4, desc=stripesize"`
+	SysChunkArraySize uint32 `bin:"off=a0, siz=4, desc=sys_chunk_array_size"`
+
+	ChunkRootGeneration uint64 `bin:"off=a4, siz=8, desc=chunk_root_generation"`
+	CompatFlags         uint64 `bin:"off=ac, siz=8, desc=compat_flags"`
+	CompatROFlags       uint64 `bin:"off=b4, siz=8, desc=compat_ro_flags - only implementations that support the flags can write to the filesystem"`
+	IncompatFlags       uint64 `bin:"off=bc, siz=8, desc=incompat_flags - only implementations that support the flags can use the filesystem"`
+	ChecksumType        uint16 `bin:"off=c4, siz=2, desc=csum_type - Btrfs currently uses the CRC32c little-endian hash function with seed -1."`
+
+	RootLevel  uint8 `bin:"off=c6, siz=1, desc=root_level"`
+	ChunkLevel uint8 `bin:"off=c7, siz=1, desc=chunk_root_level"`
+	LogLevel   uint8 `bin:"off=c8, siz=1, desc=log_root_level"`
+
+	DevItem            DevItem     `bin:"off=c9,  siz=62,  desc=DEV_ITEM data for this device"`
+	Label              [0x100]byte `bin:"off=12b, siz=100, desc=label (may not contain '/' or '\\')"`
+	CacheGeneration    uint64      `bin:"off=22b, siz=8,   desc=cache_generation"`
+	UUIDTreeGeneration uint64      `bin:"off=233, siz=8,   desc=uuid_tree_generation"`
+
+	Reserved [0xf0]byte `bin:"off=23b, siz=f0,  desc=reserved /* future expansion */"`
+
+	TODOSysChunkArray [0x800]byte `bin:"off=32b, siz=800, desc=sys_chunk_array:(n bytes valid) Contains (KEY . CHUNK_ITEM) pairs for all SYSTEM chunks. This is needed to bootstrap the mapping from logical addresses to physical. "`
+	TODOSuperRoots    [0x2a0]byte `bin:"off=b2b, siz=2a0, desc=Contain super_roots (4 btrfs_root_backup)"`
+
+	Unused [0x235]byte `bin:"off=dcb, siz=235, desc=current unused"`
+
+	binstruct.End `bin:"off=1000"`
+}
+
+func (sb Superblock) CalculateChecksum() (CSum, error) {
+	data, err := binstruct.Marshal(sb)
+	if err != nil {
+		return CSum{}, err
+	}
+	return CRC32c(data[0x20:]), nil
+}
+
+type DevItem struct {
+	DeviceID uint64 `bin:"off=0,    siz=8,  desc=device id"`
+
+	NumBytes     uint64 `bin:"off=8,    siz=8,  desc=number of bytes"`
+	NumBytesUsed uint64 `bin:"off=10,   siz=8,  desc=number of bytes used"`
+
+	IOOptimalAlign uint32 `bin:"off=18,   siz=4,  desc=optimal I/O align"`
+	IOOptimalWidth uint32 `bin:"off=1c,   siz=4,  desc=optimal I/O width"`
+	IOMinSize      uint32 `bin:"off=20,   siz=4,  desc=minimal I/O size (sector size)"`
+
+	Type        uint64 `bin:"off=24,   siz=8,  desc=type"`
+	Generation  uint64 `bin:"off=2c,   siz=8,  desc=generation"`
+	StartOffset uint64 `bin:"off=34,   siz=8,  desc=start offset"`
+	DevGroup    uint32 `bin:"off=3c,   siz=4,  desc=dev group"`
+	SeekSpeed   uint8  `bin:"off=40,   siz=1,  desc=seek speed"`
+	Bandwidth   uint8  `bin:"off=41,   siz=1,  desc=bandwidth"`
+
+	DevUUID UUID `bin:"off=42,   siz=10,         desc=device UUID"`
+	FSUUID  UUID `bin:"off=52,   siz=10,         desc=FS UUID"`
+
+	binstruct.End `bin:"off=62"`
+}
+
+type ChunkItem struct {
+	// Maps logical address to physical.
+	Size           uint64 `bin:"off=0,  siz=8, desc=size of chunk (bytes)"`
+	Root           ObjID  `bin:"off=8,  siz=8, desc=root referencing this chunk (2)"`
+	StripeLen      uint64 `bin:"off=10, siz=8, desc=stripe length"`
+	Type           uint64 `bin:"off=18, siz=8, desc=type (same as flags for block group?)"`
+	IOOptimalAlign uint32 `bin:"off=20, siz=4, desc=optimal io alignment"`
+	IOOptimalWidth uint32 `bin:"off=24, siz=4, desc=optimal io width"`
+	IoMinSize      uint32 `bin:"off=28, siz=4, desc=minimal io size (sector size)"`
+	NumStripes     uint16 `bin:"off=2c, siz=2, desc=number of stripes"`
+	SubStripes     uint16 `bin:"off=2e, siz=2, desc=sub stripes"`
+	binstruct.End  `bin:"off=30"`
+}
+
+type ChunkItemStripe struct {
+	// Stripes follow (for each number of stripes):
+	DeviceID      ObjID  `bin:"off=0,  siz=8,  desc=device id"`
+	Offset        uint64 `bin:"off=8,  siz=8,  desc=offset"`
+	DeviceUUID    UUID   `bin:"off=10, siz=10, desc=device UUID"`
+	binstruct.End `bin:"off=20"`
+}
diff --git a/pkg/btrfs/uuid.go b/pkg/btrfs/uuid.go
new file mode 100644
index 0000000..5218a3f
--- /dev/null
+++ b/pkg/btrfs/uuid.go
@@ -0,0 +1,19 @@
+package btrfs
+
+import (
+	"encoding/hex"
+	"strings"
+)
+
+type UUID [16]byte
+
+func (uuid UUID) String() string {
+	str := hex.EncodeToString(uuid[:])
+	return strings.Join([]string{
+		str[:8],
+		str[8:12],
+		str[12:16],
+		str[16:20],
+		str[20:32],
+	}, "-")
+}