cmd/sharefs: implement shared filesystem

This is for passing files between applications, similar to android /sdcard.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/sharefs/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"log"
+	"os"
+	"path"
+	"runtime"
+	"syscall"
+)
+
+// executableName is the [path.Base] name of the executable that started the current process.
+var executableName = func() string {
+	if len(os.Args) > 0 {
+		return path.Base(os.Args[0])
+	} else if name, err := os.Executable(); err != nil {
+		return "sharefs"
+	} else {
+		return path.Base(name)
+	}
+}()
+
+func main() {
+	runtime.LockOSThread()
+	log.SetFlags(0)
+	log.SetPrefix(executableName + ": ")
+
+	// don't mask creation mode, kernel already did that
+	syscall.Umask(0)
+
+	os.Exit(_main(len(os.Args), copyStrings(os.Args...)))
+}