From 3cfb784b4e863da8034f4b9bd58c8ec50487ebfb Mon Sep 17 00:00:00 2001
From: Felicitas Pojtinger <felicitas@pojtinger.com>
Date: Sun, 14 Nov 2021 19:57:59 +0100
Subject: [PATCH] feat: Add basic write support

---
 cmd/stfs-eod/main.go                          |   4 +-
 cmd/stfs-metadata/main.go                     |   5 +
 .../main.go                                   |   0
 cmd/stfs-tvf/main.go                          |   5 +
 cmd/stfs-uvf/main.go                          | 120 ++++++++++++++++++
 5 files changed, 131 insertions(+), 3 deletions(-)
 rename cmd/{stfs-seek-disk => stfs-seek-tape}/main.go (100%)
 create mode 100644 cmd/stfs-uvf/main.go

diff --git a/cmd/stfs-eod/main.go b/cmd/stfs-eod/main.go
index f593689..cc69e6e 100644
--- a/cmd/stfs-eod/main.go
+++ b/cmd/stfs-eod/main.go
@@ -22,7 +22,6 @@ type Operation struct {
 
 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()
 
@@ -38,8 +37,7 @@ func main() {
 		MTIOCTOP,
 		uintptr(unsafe.Pointer(
 			&Operation{
-				Op:    MTEOM,
-				Count: int32(*record),
+				Op: MTEOM,
 			},
 		)),
 	)
diff --git a/cmd/stfs-metadata/main.go b/cmd/stfs-metadata/main.go
index dccd386..0042ebc 100644
--- a/cmd/stfs-metadata/main.go
+++ b/cmd/stfs-metadata/main.go
@@ -97,6 +97,11 @@ func main() {
 				break
 			}
 
+			// Missing trailer (expected for concatenated tars)
+			if err == io.ErrUnexpectedEOF {
+				break
+			}
+
 			panic(err)
 		}
 
diff --git a/cmd/stfs-seek-disk/main.go b/cmd/stfs-seek-tape/main.go
similarity index 100%
rename from cmd/stfs-seek-disk/main.go
rename to cmd/stfs-seek-tape/main.go
diff --git a/cmd/stfs-tvf/main.go b/cmd/stfs-tvf/main.go
index a3cef1d..fb9071a 100644
--- a/cmd/stfs-tvf/main.go
+++ b/cmd/stfs-tvf/main.go
@@ -60,6 +60,11 @@ func main() {
 				break
 			}
 
+			// Missing trailer (expected for concatenated tars)
+			if err == io.ErrUnexpectedEOF {
+				break
+			}
+
 			panic(err)
 		}
 
diff --git a/cmd/stfs-uvf/main.go b/cmd/stfs-uvf/main.go
new file mode 100644
index 0000000..659f897
--- /dev/null
+++ b/cmd/stfs-uvf/main.go
@@ -0,0 +1,120 @@
+package main
+
+import (
+	"archive/tar"
+	"flag"
+	"io"
+	"io/fs"
+	"log"
+	"os"
+	"path/filepath"
+	"syscall"
+	"unsafe"
+)
+
+// See https://github.com/benmcclelland/mtio
+const (
+	MTIOCTOP = 0x40086d01 // Do magnetic tape operation
+	MTEOM    = 12         // Goto end of recorded media (for appending files)
+)
+
+// 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 (tape drive or tar file) to open")
+	dir := flag.String("dir", ".", "Directory to add to the file")
+
+	flag.Parse()
+
+	isRegular := true
+	stat, err := os.Stat(*file)
+	if err == nil {
+		isRegular = stat.Mode().IsRegular()
+	} else {
+		if os.IsNotExist(err) {
+			isRegular = true
+		} else {
+			panic(err)
+		}
+	}
+
+	var f *os.File
+	if isRegular {
+		f, err = os.OpenFile(*file, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
+		if err != nil {
+			panic(err)
+		}
+
+		// No need to go to end manually due to `os.O_APPEND`
+	} else {
+		// Go to end of file
+		syscall.Syscall(
+			syscall.SYS_IOCTL,
+			f.Fd(),
+			MTIOCTOP,
+			uintptr(unsafe.Pointer(
+				&Operation{
+					Op: MTEOM,
+				},
+			)),
+		)
+
+		f, err = os.OpenFile(*file, os.O_APPEND|os.O_WRONLY, os.ModeCharDevice)
+		if err != nil {
+			panic(err)
+		}
+	}
+	defer f.Close()
+
+	tw := tar.NewWriter(f) // We are not closing the tar writer to prevent writing the trailer
+
+	if err := filepath.Walk(*dir, func(path string, info fs.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		link := ""
+		if info.Mode()&os.ModeSymlink == os.ModeSymlink {
+			if link, err = os.Readlink(path); err != nil {
+				return err
+			}
+		}
+
+		hdr, err := tar.FileInfoHeader(info, link)
+		if err != nil {
+			return err
+		}
+
+		hdr.Name = path
+
+		log.Println(hdr)
+
+		if err := tw.WriteHeader(hdr); err != nil {
+			return err
+		}
+
+		// Skip writing non-regular files
+		if !info.Mode().IsRegular() {
+			return nil
+		}
+
+		file, err := os.Open(path)
+		if err != nil {
+			return err
+		}
+		defer file.Close()
+
+		if _, err := io.Copy(tw, file); err != nil {
+			return err
+		}
+
+		return nil
+	}); err != nil {
+		panic(err)
+	}
+}