add BlockDevice

sd/blockdevice.go

@@ -0,0 +1,150 @@
+package sd
+
+import (
+	"errors"
+	"math/bits"
+)
+
+var (
+	errNegativeOffset = errors.New("sd: negative offset")
+)
+
+type Card interface {
+	WriteBlocks(data []byte, startBlockIdx int64) error
+	ReadBlocks(dst []byte, startBlockIdx int64) error
+	EraseBlockSize() int64
+	EraseBlocks(start, len int64) error
+}
+
+func NewBlockDevice(card Card, blockSize int, numBlocks int64) *BlockDevice {
+	if card == nil || blockSize <= 0 {
+		panic("invalid arguments")
+	}
+	tz := bits.TrailingZeros(uint(blockSize))
+	if blockSize>>tz != 1 {
+		panic("blockSize must be a power of 2")
+	}
+	bd := &BlockDevice{
+		card:       card,
+		blockbuf:   make([]byte, blockSize),
+		blockshift: tz,
+		blockmask:  (1 << tz) - 1,
+		numblocks:  numBlocks,
+	}
+	return bd
+}
+
+// BlockDevice implements tinyfs.BlockDevice interface.
+type BlockDevice struct {
+	card       Card
+	blockbuf   []byte
+	blockshift int
+	blockmask  int64
+	numblocks  int64
+}
+
+func (bd *BlockDevice) moduloBlockSize(n int64) int64 {
+	return n &^ bd.blockmask
+}
+
+func (bd *BlockDevice) divideBlockSize(n int64) int64 {
+	return n >> bd.blockshift
+}
+
+func (bd *BlockDevice) ReadAt(p []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errNegativeOffset
+	}
+	blockSize := len(bd.blockbuf)
+	blockIdx := bd.divideBlockSize(off)
+	blockOff := bd.moduloBlockSize(off)
+	if blockOff != 0 {
+		// Non-aligned first block case.
+		if err := bd.card.ReadBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+		n += copy(p, bd.blockbuf[blockOff:])
+		p = p[n:]
+		blockIdx++
+	}
+
+	remaining := len(p) - n
+	if remaining >= blockSize {
+		// 1 or more full blocks case.
+		endOffset := remaining - int(bd.moduloBlockSize(int64(remaining)))
+		err = bd.card.ReadBlocks(p[:endOffset], blockIdx)
+		if err != nil {
+			return n, err
+		}
+		p = p[endOffset:]
+		n += endOffset
+		blockIdx += int64(endOffset / blockSize)
+	}
+
+	if len(p) > 0 {
+		// Non-aligned last block case.
+		if err := bd.card.ReadBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+		n += copy(p, bd.blockbuf)
+	}
+	return n, nil
+}
+
+func (bd *BlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errNegativeOffset
+	}
+	blockSize := len(bd.blockbuf)
+	blockIdx := bd.divideBlockSize(off)
+	blockOff := bd.moduloBlockSize(off)
+	if blockOff != 0 {
+		// Non-aligned first block case.
+		if err := bd.card.ReadBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+		n += copy(bd.blockbuf[blockOff:], p)
+		if err := bd.card.WriteBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+		p = p[n:]
+		blockIdx++
+	}
+
+	remaining := len(p) - n
+	if remaining >= blockSize {
+		// 1 or more full blocks case.
+		endOffset := remaining - int(bd.moduloBlockSize(int64(remaining)))
+		err = bd.card.WriteBlocks(p[:endOffset], blockIdx)
+		if err != nil {
+			return n, err
+		}
+		p = p[endOffset:]
+		n += endOffset
+		blockIdx += int64(endOffset / blockSize)
+	}
+
+	if len(p) > 0 {
+		// Non-aligned last block case.
+		if err := bd.card.ReadBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+		n += copy(bd.blockbuf, p)
+		if err := bd.card.WriteBlocks(bd.blockbuf, blockIdx); err != nil {
+			return n, err
+		}
+	}
+	return n, nil
+}
+
+func (bd *BlockDevice) Size() int64 {
+	return int64(len(bd.blockbuf)) * bd.numblocks
+}
+
+func (bd *BlockDevice) EraseBlocks(start, len int64) error {
+	return bd.card.EraseBlocks(start, len)
+}
+
+func (bd *BlockDevice) EraseBlockSize() int64 {
+	return bd.card.EraseBlockSize()
+}