1 files changed, 105 insertions, 0 deletions
diff --git a/cmd/btrfs-dbg/main.go b/cmd/btrfs-dbg/main.go
new file mode 100644
index 0000000..8758cd0
--- /dev/null
+++ b/cmd/btrfs-dbg/main.go
@@ -0,0 +1,105 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"lukeshu.com/btrfs-tools/pkg/binstruct"
+)
+
+func main() {
+	if err := Main(os.Args[1]); err != nil {
+		fmt.Fprintf(os.Stderr, "%s: error: %v\n", os.Args[0], err)
+		os.Exit(1)
+	}
+}
+
+func Main(imgfilename string) (err error) {
+	maybeSetErr := func(_err error) {
+		if _err != nil && err == nil {
+			err = _err
+		}
+	}
+
+	fh, err := os.Open(imgfilename)
+	if err != nil {
+		return err
+	}
+	img := &Img{
+		File: fh,
+	}
+	defer func() {
+		maybeSetErr(img.Close())
+	}()
+
+	superblocks, err := img.Superblocks()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("%#v\n", superblocks[0])
+
+	return nil
+}
+
+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
+}