feat: Add cmd to seek to specific block

cmd/stfs-seek/main.go

@@ -7,7 +7,7 @@ import (
 	"unsafe"
 )
 
-// See https://github.com/benmcclelland/mtio/blob/f929531fb4fe6433f7198ccd89d1c1414ef8fa3f/mtst.go#L46
+// See https://github.com/benmcclelland/mtio
 const (
 	MTIOCTOP = 0x40086d01 // Do magnetic tape operation
 	MTSEEK   = 22         // Seek to block
@@ -15,11 +15,9 @@ const (
 
 // Operation is struct for MTIOCTOP
 type Operation struct {
-	op int16 // Operation ID
-
-	pad int16 // Padding to match C structures
-
-	count int32 // Operation count
+	Op    int16 // Operation ID
+	Pad   int16 // Padding to match C structures
+	Count int32 // Operation count
 }
 
 func main() {
@@ -40,8 +38,8 @@ func main() {
 		MTIOCTOP,
 		uintptr(unsafe.Pointer(
 			&Operation{
-				op:    MTSEEK,
-				count: int32(*record),
+				Op:    MTSEEK,
+				Count: int32(*record),
 			},
 		)),
 	)

cmd/stfs-tell/main.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// See https://github.com/benmcclelland/mtio
+const (
+	MTIOCPOS = 0x80086d03 // Get tape position
+)
+
+// Position is struct for MTIOCPOS
+type Position struct {
+	BlkNo int64 // Current block number
+}
+
+func main() {
+	file := flag.String("file", "/dev/nst0", "File of tape drive to open")
+
+	flag.Parse()
+
+	f, err := os.OpenFile(*file, os.O_RDONLY, os.ModeCharDevice)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	pos := &Position{}
+
+	syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		MTIOCPOS,
+		uintptr(unsafe.Pointer(pos)),
+	)
+
+	fmt.Println(pos.BlkNo)
+}