refactor: Decompose syscalls into pkg, start adding utility commands

pkg/controllers/tape.go

@@ -0,0 +1,98 @@
+package controllers
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// See https://github.com/benmcclelland/mtio
+const (
+	mtioCpos = 0x80086d03 // Get tape position
+	mtioCtop = 0x40086d01 // Do magnetic tape operation
+
+	mtFsf  = 1  // Forward space over FileMark, position at first record of next file
+	mtEom  = 12 // Goto end of recorded media (for appending files)
+	mtSeek = 22 // Seek to block
+
+	BlockSize = 512
+)
+
+// position is struct for MTIOCPOS
+type position struct {
+	blkNo int64 // Current block number
+}
+
+// operation is struct for MTIOCTOP
+type operation struct {
+	op    int16 // Operation ID
+	pad   int16 // Padding to match C structures
+	count int32 // Operation count
+}
+
+func GoToEndOfTape(f *os.File) error {
+	if _, _, err := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		mtioCtop,
+		uintptr(unsafe.Pointer(
+			&operation{
+				op: mtEom,
+			},
+		)),
+	); err != 0 {
+		return err
+	}
+
+	return nil
+}
+
+func GoToNextFileOnTape(f *os.File) error {
+	if _, _, err := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		mtioCtop,
+		uintptr(unsafe.Pointer(
+			&operation{
+				op:    mtFsf,
+				count: 1,
+			},
+		)),
+	); err != 0 {
+		return err
+	}
+
+	return nil
+}
+
+func GetCurrentRecordFromTape(f *os.File) (int64, error) {
+	pos := &position{}
+	if _, _, err := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		mtioCpos,
+		uintptr(unsafe.Pointer(pos)),
+	); err != 0 {
+		return 0, err
+	}
+
+	return pos.blkNo, nil
+}
+
+func SeekToRecordOnTape(f *os.File, record int32) error {
+	if _, _, err := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		mtioCtop,
+		uintptr(unsafe.Pointer(
+			&operation{
+				op:    mtSeek,
+				count: record,
+			},
+		)),
+	); err != 0 {
+		return err
+	}
+
+	return nil
+}