diff --git a/vfs/make_open_tests.go b/vfs/make_open_tests.go
new file mode 100644
index 000000000..8e0a773ba
--- /dev/null
+++ b/vfs/make_open_tests.go
@@ -0,0 +1,228 @@
+// This makes the open test suite
+//
+// Run with go run make_open_tests.go | gofmt > open_test.go
+//
+//+build none
+
+// FIXME include read too?
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"strings"
+)
+
+// Interprets err into a vfs error
+func whichError(err error) string {
+	switch err {
+	case nil:
+		return "nil"
+	case io.EOF:
+		return "io.EOF"
+	}
+	s := err.Error()
+	switch {
+	case strings.Contains(s, "no such file or directory"):
+		return "ENOENT"
+	case strings.Contains(s, "bad file descriptor"):
+		return "EBADF"
+	case strings.Contains(s, "file exists"):
+		return "EEXIST"
+	}
+	log.Fatalf("Unknown error: %v", err)
+	return ""
+}
+
+// test Opening, reading and writing the file handle with the flags given
+func test(fileName string, flags int, mode string) {
+	// first try with file not existing
+	_, err := os.Stat(fileName)
+	if !os.IsNotExist(err) {
+		log.Fatalf("File must not exist")
+	}
+	f, openNonExistentErr := os.OpenFile(fileName, flags, 0666)
+
+	var readNonExistentErr error
+	var writeNonExistentErr error
+	if openNonExistentErr == nil {
+		// read some bytes
+		buf := []byte{0, 0}
+		_, readNonExistentErr = f.Read(buf)
+
+		// write some bytes
+		_, writeNonExistentErr = f.Write([]byte("hello"))
+
+		// close
+		err = f.Close()
+		if err != nil {
+			log.Fatalf("failed to close: %v", err)
+		}
+	}
+
+	// write the file
+	f, err = os.Create(fileName)
+	if err != nil {
+		log.Fatalf("failed to create: %v", err)
+	}
+	n, err := f.Write([]byte("hello"))
+	if n != 5 || err != nil {
+		log.Fatalf("failed to write n=%d: %v", n, err)
+	}
+	// close
+	err = f.Close()
+	if err != nil {
+		log.Fatalf("failed to close: %v", err)
+	}
+
+	// then open file and try with file existing
+
+	f, openExistingErr := os.OpenFile(fileName, flags, 0666)
+	var readExistingErr error
+	var writeExistingErr error
+	if openExistingErr == nil {
+		// read some bytes
+		buf := []byte{0, 0}
+		_, readExistingErr = f.Read(buf)
+
+		// write some bytes
+		n, writeExistingErr = f.Write([]byte("HEL"))
+
+		// close
+		err = f.Close()
+		if err != nil {
+			log.Fatalf("failed to close: %v", err)
+		}
+	}
+
+	// read the file
+	f, err = os.Open(fileName)
+	if err != nil {
+		log.Fatalf("failed to open: %v", err)
+	}
+	var buf = make([]byte, 64)
+	n, err = f.Read(buf)
+	if err != nil && err != io.EOF {
+		log.Fatalf("failed to read n=%d: %v", n, err)
+	}
+	err = f.Close()
+	if err != nil {
+		log.Fatalf("failed to close: %v", err)
+	}
+	contents := string(buf[:n])
+
+	// remove file
+	err = os.Remove(fileName)
+	if err != nil {
+		log.Fatalf("failed to remove: %v", err)
+	}
+
+	// output the struct
+	fmt.Printf(`{
+	flags: %s,
+	what: %q,
+	openNonExistentErr: %s,
+	readNonExistentErr: %s,
+	writeNonExistentErr: %s,
+	openExistingErr: %s,
+	readExistingErr: %s,
+	writeExistingErr: %s,
+	contents: %q,
+},`,
+		mode,
+		mode,
+		whichError(openNonExistentErr),
+		whichError(readNonExistentErr),
+		whichError(writeNonExistentErr),
+		whichError(openExistingErr),
+		whichError(readExistingErr),
+		whichError(writeExistingErr),
+		contents)
+}
+
+func main() {
+	fmt.Printf(`// data generated by go run make_open_tests.go | gofmt > open_test.go
+
+package vfs
+
+import (
+	"os"
+	"io"
+)
+
+// openTest describes a test of OpenFile
+type openTest struct{
+	flags int
+	what string
+	openNonExistentErr error
+	readNonExistentErr error
+	writeNonExistentErr error
+	openExistingErr error
+	readExistingErr error
+	writeExistingErr error
+	contents string
+}
+
+// openTests is a suite of tests for OpenFile with all possible
+// combination of flags.  This obeys Unix semantics even on Windows.
+var openTests = []openTest{
+`)
+	f, err := ioutil.TempFile("", "open-test")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fileName := f.Name()
+	_ = f.Close()
+	err = os.Remove(fileName)
+	if err != nil {
+		log.Fatalf("failed to remove: %v", err)
+	}
+	for _, rwMode := range []int{os.O_RDONLY, os.O_WRONLY, os.O_RDWR} {
+		flags0 := rwMode
+		parts0 := []string{"os.O_RDONLY", "os.O_WRONLY", "os.O_RDWR"}[rwMode : rwMode+1]
+		for _, appendMode := range []int{0, os.O_APPEND} {
+			flags1 := flags0 | appendMode
+			parts1 := parts0
+			if appendMode != 0 {
+				parts1 = append(parts1, "os.O_APPEND")
+			}
+			for _, createMode := range []int{0, os.O_CREATE} {
+				flags2 := flags1 | createMode
+				parts2 := parts1
+				if createMode != 0 {
+					parts2 = append(parts2, "os.O_CREATE")
+				}
+				for _, exclMode := range []int{0, os.O_EXCL} {
+					flags3 := flags2 | exclMode
+					parts3 := parts2
+					if exclMode != 0 {
+						parts3 = append(parts2, "os.O_EXCL")
+					}
+					for _, syncMode := range []int{0, os.O_SYNC} {
+						flags4 := flags3 | syncMode
+						parts4 := parts3
+						if syncMode != 0 {
+							parts4 = append(parts4, "os.O_SYNC")
+						}
+						for _, truncMode := range []int{0, os.O_TRUNC} {
+							flags5 := flags4 | truncMode
+							parts5 := parts4
+							if truncMode != 0 {
+								parts5 = append(parts5, "os.O_TRUNC")
+							}
+							textMode := strings.Join(parts5, "|")
+							flags := flags5
+
+							test(fileName, flags, textMode)
+						}
+					}
+				}
+			}
+		}
+	}
+	fmt.Printf("\n}\n")
+}
diff --git a/vfs/open_test.go b/vfs/open_test.go
new file mode 100644
index 000000000..6ff4b65e6
--- /dev/null
+++ b/vfs/open_test.go
@@ -0,0 +1,987 @@
+// data generated by go run make_open_tests.go | gofmt > open_test.go
+
+package vfs
+
+import (
+	"io"
+	"os"
+)
+
+// openTest describes a test of OpenFile
+type openTest struct {
+	flags               int
+	what                string
+	openNonExistentErr  error
+	readNonExistentErr  error
+	writeNonExistentErr error
+	openExistingErr     error
+	readExistingErr     error
+	writeExistingErr    error
+	contents            string
+}
+
+// openTests is a suite of tests for OpenFile with all possible
+// combination of flags.  This obeys Unix semantics even on Windows.
+var openTests = []openTest{
+	{
+		flags:               os.O_RDONLY,
+		what:                "os.O_RDONLY",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_EXCL,
+		what:                "os.O_RDONLY|os.O_EXCL",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE,
+		what:                "os.O_RDONLY|os.O_CREATE",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_EXCL,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_EXCL",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_CREATE | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_CREATE|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND,
+		what:                "os.O_RDONLY|os.O_APPEND",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_EXCL,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_EXCL",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    EBADF,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    EBADF,
+		contents:            "",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_EXCL,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_EXCL",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDONLY | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDONLY|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: EBADF,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_WRONLY,
+		what:                "os.O_WRONLY",
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+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_SYNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "helloHEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    nil,
+		contents:            "HEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_EXCL,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_EXCL",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "helloHEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    nil,
+		contents:            "HEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "helloHEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  ENOENT,
+		readNonExistentErr:  nil,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    nil,
+		contents:            "HEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "helloHEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    nil,
+		contents:            "HEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_SYNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "helloHEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     nil,
+		readExistingErr:     io.EOF,
+		writeExistingErr:    nil,
+		contents:            "HEL",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_EXCL,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_EXCL",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_SYNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_SYNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	}, {
+		flags:               os.O_RDWR | os.O_APPEND | os.O_CREATE | os.O_EXCL | os.O_SYNC | os.O_TRUNC,
+		what:                "os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_EXCL|os.O_SYNC|os.O_TRUNC",
+		openNonExistentErr:  nil,
+		readNonExistentErr:  io.EOF,
+		writeNonExistentErr: nil,
+		openExistingErr:     EEXIST,
+		readExistingErr:     nil,
+		writeExistingErr:    nil,
+		contents:            "hello",
+	},
+}
diff --git a/vfs/read_write.go b/vfs/read_write.go
index d66bb3d77..72a96f1b9 100644
--- a/vfs/read_write.go
+++ b/vfs/read_write.go
@@ -3,6 +3,7 @@ package vfs
 import (
 	"io"
 	"os"
+	"runtime"
 	"sync"
 
 	"github.com/ncw/rclone/fs"
@@ -44,6 +45,11 @@ func newRWFileHandle(d *Dir, f *File, remote string, flags int) (fh *RWFileHandl
 		return nil, errors.Wrap(err, "open RW handle failed to make cache directory")
 	}
 
+	// if O_CREATE and O_EXCL are set and if path already exists, then return EEXIST
+	if flags&(os.O_CREATE|os.O_EXCL) == os.O_CREATE|os.O_EXCL && f.exists() {
+		return nil, EEXIST
+	}
+
 	fh = &RWFileHandle{
 		o:      f.o,
 		file:   f,
@@ -69,6 +75,8 @@ func (fh *RWFileHandle) openPending(truncate bool) (err error) {
 		return nil
 	}
 
+	cacheFileOpenFlags := fh.flags
+
 	// if not truncating the file, need to read it first
 	if fh.flags&os.O_TRUNC == 0 && !truncate {
 		// Fetch the file if it hasn't changed
@@ -92,12 +100,30 @@ func (fh *RWFileHandle) openPending(truncate bool) (err error) {
 			}
 		}
 	} else {
-		// Set the size to 0 since we are truncating
+		// Set the size to 0 since we are truncating and flag we need to write it back
 		fh.file.setSize(0)
+		fh.writeCalled = true
+		if fh.flags&os.O_CREATE != 0 && fh.file.exists() {
+			// create and empty file if it exists on the source
+			cacheFileOpenFlags |= os.O_CREATE
+		}
+		// Windows doesn't seem to deal well with O_TRUNC and
+		// certain access modes so so truncate the file if it
+		// exists in these cases.
+		if runtime.GOOS == "windows" && (fh.flags&accessModeMask == os.O_RDONLY || fh.flags|os.O_APPEND != 0) {
+			cacheFileOpenFlags &^= os.O_TRUNC
+			_, err = os.Stat(fh.osPath)
+			if err == nil {
+				err = os.Truncate(fh.osPath, 0)
+				if err != nil {
+					return errors.Wrap(err, "cache open failed to truncate")
+				}
+			}
+		}
 	}
 
 	fs.Debugf(fh.remote, "Opening cached copy with flags=%s", decodeOpenFlags(fh.flags))
-	fd, err := os.OpenFile(fh.osPath, fh.flags|os.O_CREATE, 0600)
+	fd, err := os.OpenFile(fh.osPath, cacheFileOpenFlags, 0600)
 	if err != nil {
 		return errors.Wrap(err, "cache open file failed")
 	}
@@ -180,8 +206,8 @@ func (fh *RWFileHandle) close() (err error) {
 
 	// FIXME measure whether we actually did any writes or not -
 	// no writes means no transfer?
-	if rdwrMode == os.O_RDONLY {
-		fs.Debugf(fh.remote, "read only so not transferring")
+	if rdwrMode == os.O_RDONLY && fh.flags&os.O_TRUNC == 0 {
+		fs.Debugf(fh.remote, "read only and not truncating so not transferring")
 		return nil
 	}
 
@@ -302,30 +328,35 @@ func (fh *RWFileHandle) Stat() (os.FileInfo, error) {
 	return fh.file, nil
 }
 
-// Read bytes from the file
-func (fh *RWFileHandle) Read(b []byte) (n int, err error) {
+// readFn is a general purpose read function - pass in a closure to do
+// the actual read
+func (fh *RWFileHandle) readFn(read func() (int, error)) (n int, err error) {
 	fh.mu.Lock()
 	defer fh.mu.Unlock()
 	if fh.closed {
 		return 0, ECLOSED
 	}
+	if fh.flags&accessModeMask == os.O_WRONLY {
+		return 0, EBADF
+	}
 	if err = fh.openPending(false); err != nil {
 		return n, err
 	}
-	return fh.File.Read(b)
+	return read()
+}
+
+// Read bytes from the file
+func (fh *RWFileHandle) Read(b []byte) (n int, err error) {
+	return fh.readFn(func() (int, error) {
+		return fh.File.Read(b)
+	})
 }
 
 // ReadAt bytes from the file at off
 func (fh *RWFileHandle) ReadAt(b []byte, off int64) (n int, err error) {
-	fh.mu.Lock()
-	defer fh.mu.Unlock()
-	if fh.closed {
-		return 0, ECLOSED
-	}
-	if err = fh.openPending(false); err != nil {
-		return n, err
-	}
-	return fh.File.ReadAt(b, off)
+	return fh.readFn(func() (int, error) {
+		return fh.File.ReadAt(b, off)
+	})
 }
 
 // Seek to new file position
@@ -350,6 +381,9 @@ func (fh *RWFileHandle) writeFn(write func() error) (err error) {
 	if fh.closed {
 		return ECLOSED
 	}
+	if fh.flags&accessModeMask == os.O_RDONLY {
+		return EBADF
+	}
 	if err = fh.openPending(false); err != nil {
 		return err
 	}
@@ -421,5 +455,8 @@ func (fh *RWFileHandle) Sync() error {
 	if !fh.opened {
 		return nil
 	}
+	if fh.flags&accessModeMask == os.O_RDONLY {
+		return nil
+	}
 	return fh.File.Sync()
 }
diff --git a/vfs/read_write_test.go b/vfs/read_write_test.go
index 6f482cf5a..90713e631 100644
--- a/vfs/read_write_test.go
+++ b/vfs/read_write_test.go
@@ -2,6 +2,7 @@ package vfs
 
 import (
 	"io"
+	"io/ioutil"
 	"os"
 	"testing"
 
@@ -286,6 +287,10 @@ func TestRWFileHandleMethodsWrite(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, 7, n)
 
+	// Sync
+	err = fh.Sync()
+	assert.NoError(t, err)
+
 	// Stat
 	var fi os.FileInfo
 	fi, err = fh.Stat()
@@ -434,3 +439,87 @@ func TestRWFileHandleReleaseWrite(t *testing.T) {
 	assert.NoError(t, err)
 	assert.True(t, fh.closed)
 }
+
+func testRWFileHandleOpenTest(t *testing.T, vfs *VFS, test *openTest) {
+	fileName := "open-test-file"
+
+	// first try with file not existing
+	_, err := vfs.Stat(fileName)
+	require.True(t, os.IsNotExist(err), test.what)
+
+	f, openNonExistentErr := vfs.OpenFile(fileName, test.flags, 0666)
+
+	var readNonExistentErr error
+	var writeNonExistentErr error
+	if openNonExistentErr == nil {
+		// read some bytes
+		buf := []byte{0, 0}
+		_, readNonExistentErr = f.Read(buf)
+
+		// write some bytes
+		_, writeNonExistentErr = f.Write([]byte("hello"))
+
+		// close
+		err = f.Close()
+		require.NoError(t, err, test.what)
+	}
+
+	// write the file
+	f, err = vfs.OpenFile(fileName, os.O_WRONLY|os.O_CREATE, 0777)
+	require.NoError(t, err, test.what)
+	_, err = f.Write([]byte("hello"))
+	require.NoError(t, err, test.what)
+	err = f.Close()
+	require.NoError(t, err, test.what)
+
+	// then open file and try with file existing
+
+	f, openExistingErr := vfs.OpenFile(fileName, test.flags, 0666)
+	var readExistingErr error
+	var writeExistingErr error
+	if openExistingErr == nil {
+		// read some bytes
+		buf := []byte{0, 0}
+		_, readExistingErr = f.Read(buf)
+
+		// write some bytes
+		_, writeExistingErr = f.Write([]byte("HEL"))
+
+		// close
+		err = f.Close()
+		require.NoError(t, err, test.what)
+	}
+
+	// read the file
+	f, err = vfs.OpenFile(fileName, os.O_RDONLY, 0)
+	require.NoError(t, err, test.what)
+	buf, err := ioutil.ReadAll(f)
+	require.NoError(t, err, test.what)
+	err = f.Close()
+	require.NoError(t, err, test.what)
+	contents := string(buf)
+
+	// remove file
+	node, err := vfs.Stat(fileName)
+	require.NoError(t, err, test.what)
+	err = node.Remove()
+	require.NoError(t, err, test.what)
+
+	// check
+	assert.Equal(t, test.readNonExistentErr, readNonExistentErr, "readNonExistentErr: %s: want=%v, got=%v", test.what, test.readNonExistentErr, readNonExistentErr)
+	assert.Equal(t, test.writeNonExistentErr, writeNonExistentErr, "writeNonExistentErr: %s: want=%v, got=%v", test.what, test.writeNonExistentErr, writeNonExistentErr)
+	assert.Equal(t, test.readExistingErr, readExistingErr, "readExistingErr: %s: want=%v, got=%v", test.what, test.readExistingErr, readExistingErr)
+	assert.Equal(t, test.writeExistingErr, writeExistingErr, "writeExistingErr: %s: want=%v, got=%v", test.what, test.writeExistingErr, writeExistingErr)
+	assert.Equal(t, test.contents, contents, test.what)
+}
+
+func TestRWFileHandleOpenTests(t *testing.T) {
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+
+	vfs := New(r.Fremote, nil)
+	vfs.Opt.CacheMode = CacheModeFull
+	for _, test := range openTests {
+		testRWFileHandleOpenTest(t, vfs, &test)
+	}
+}