From 1fd2203f66f62f15a3433f35a41c7a01c3ce6d07 Mon Sep 17 00:00:00 2001
From: Felicitas Pojtinger <felicitas@pojtinger.com>
Date: Sun, 14 Nov 2021 11:52:36 +0100
Subject: [PATCH] feat: Add cmd that seeks to specific location in tape

---
 cmd/stfs-seek/main.go | 48 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 cmd/stfs-seek/main.go

diff --git a/cmd/stfs-seek/main.go b/cmd/stfs-seek/main.go
new file mode 100644
index 0000000..6d1bf50
--- /dev/null
+++ b/cmd/stfs-seek/main.go
@@ -0,0 +1,48 @@
+package main
+
+import (
+	"flag"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// See https://github.com/benmcclelland/mtio/blob/f929531fb4fe6433f7198ccd89d1c1414ef8fa3f/mtst.go#L46
+const (
+	MTIOCTOP = 0x40086d01 // Do magnetic tape operation
+	MTSEEK   = 22         // Seek to block
+)
+
+// Operation is struct for MTIOCTOP
+type Operation struct {
+	op int16 // Operation ID
+
+	pad int16 // Padding to match C structures
+
+	count int32 // Operation count
+}
+
+func main() {
+	file := flag.String("file", "/dev/nst0", "File of tape drive to open")
+	record := flag.Int("record", 0, "Record to seek too")
+
+	flag.Parse()
+
+	f, err := os.OpenFile(*file, os.O_RDONLY, os.ModeCharDevice)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	syscall.Syscall(
+		syscall.SYS_IOCTL,
+		f.Fd(),
+		MTIOCTOP,
+		uintptr(unsafe.Pointer(
+			&Operation{
+				op:    MTSEEK,
+				count: int32(*record),
+			},
+		)),
+	)
+}