fixed RBDDiffV2 format and added a ceph-import-diff example

copy.go

@@ -173,13 +173,16 @@ func (d *Decoder) isSeekableFile(writer io.Writer) (*os.File, bool) {
 }
 
 func NewEncoder(file *os.File) *Encoder {
-	return &Encoder{file: file, Format: format.RbdDiffv1}
+	return &Encoder{file: file, Format: format.RbdDiffv1, MaxSectionSize: 1 << 32}
 }
 
 // Encoder encodes a file to a stream of sparsecat data.
 type Encoder struct {
-	file     *os.File
-	Format   format.Format
+	file *os.File
+
+	Format         format.Format
+	MaxSectionSize int64
+
 	fileSize int64
 
 	currentOffset        int64
@@ -262,6 +265,12 @@ func (e *Encoder) parseSection() error {
 	}
 
 	length := end - start
+
+	if length > e.MaxSectionSize {
+		end = start + e.MaxSectionSize
+		length = e.MaxSectionSize
+	}
+
 	e.currentSectionEnd = end
 
 	_, err = e.file.Seek(start, io.SeekStart)

example/ceph-import-diff/main.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"encoding/binary"
+	"github.com/svenwiltink/sparsecat"
+	"github.com/svenwiltink/sparsecat/format"
+	"io"
+	"log"
+	"os"
+)
+
+const (
+	RBDImageHeader = "rbd image v2\n"
+	RBDImageEndTag = "E"
+
+	RBDImageDiffsV2Header = "rbd image diffs v2\n"
+	RBDImageDiffV2Header  = "rbd diff v2\n"
+)
+
+func main() {
+	log.SetFlags(log.Llongfile)
+	if len(os.Args) != 2 {
+		log.Fatalln(os.Args[0], " <file to import>")
+	}
+
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	_, err = os.Stdout.WriteString(RBDImageHeader)
+	if err != nil {
+		panic(err)
+	}
+
+	_, err = os.Stdout.WriteString(RBDImageEndTag)
+	if err != nil {
+		panic(err)
+	}
+
+	_, err = os.Stdout.WriteString(RBDImageDiffsV2Header)
+	if err != nil {
+		panic(err)
+	}
+
+	var buf [8]byte
+	binary.LittleEndian.PutUint64(buf[:], 1)
+
+	_, err = os.Stdout.Write(buf[:])
+	if err != nil {
+		panic(err)
+	}
+
+	_, err = os.Stdout.WriteString(RBDImageDiffV2Header)
+	if err != nil {
+		panic(err)
+	}
+
+	encoder := sparsecat.NewEncoder(file)
+	encoder.Format = format.RbdDiffv2
+	encoder.MaxSectionSize = 16_000_000
+
+	_, err = io.Copy(os.Stdout, encoder)
+	if err != nil {
+		panic(err)
+	}
+}

format/rbd.go

@@ -164,7 +164,7 @@ func (r rbdDiffv2) GetSectionReader(source io.Reader, section Section) (reader i
 	buf := make([]byte, headerSize)
 	buf[0] = dataIndicator
 
-	binary.LittleEndian.PutUint64(buf[1:], 16)
+	binary.LittleEndian.PutUint64(buf[1:], 16+uint64(section.Length))
 	binary.LittleEndian.PutUint64(buf[1+8:], uint64(section.Offset))
 	binary.LittleEndian.PutUint64(buf[1+8+8:], uint64(section.Length))
 

sparse_unix.go

@@ -50,16 +50,8 @@ func detectDataSection(file *os.File, offset int64) (start int64, end int64, err
 }
 
 func supportsSeekHole(file *os.File) bool {
-	var syserr syscall.Errno
-
 	_, err := unix.Seek(int(file.Fd()), 0, SEEK_DATA)
-	if errors.As(err, &syserr) {
-		if syserr == syscall.EINVAL {
-			return false
-		}
-	}
-
-	return true
+	return err == nil
 }
 
 func getBlockDeviceSize(file *os.File) (int, error) {