os: New Open API.

We replace the current Open with:
OpenFile(name, flag, perm) // same as old Open
Open(name) // same as old Open(name, O_RDONLY, 0)
Create(name) // same as old Open(name, O_RDWR|O_TRUNC|O_CREAT, 0666)

This CL includes a gofix module and full code updates: all.bash passes.
(There may be a few comments I missed.)

The interesting packages are:
        gofix
        os
Everything else is automatically generated except for hand tweaks to:
        src/pkg/io/ioutil/ioutil.go
        src/pkg/io/ioutil/tempfile.go
        src/pkg/crypto/tls/generate_cert.go
        src/cmd/goyacc/goyacc.go
        src/cmd/goyacc/units.y

R=golang-dev, bradfitzwork, rsc, r2
CC=golang-dev
https://golang.org/cl/4357052

misc/dashboard/builder/exec.go

@@ -49,7 +49,7 @@ func runLog(envv []string, logfile, dir string, argv ...string) (output string,
 	b := new(bytes.Buffer)
 	var w io.Writer = b
 	if logfile != "" {
-		f, err := os.Open(logfile, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
+		f, err := os.Create(logfile)
 		if err != nil {
 			return
 		}

misc/goplay/goplay.go

@@ -83,7 +83,7 @@ func Compile(w http.ResponseWriter, req *http.Request) {
 	}
 
 	// write request Body to x.go
-	f, err := os.Open(src, os.O_CREAT|os.O_WRONLY|os.O_TRUNC, 0666)
+	f, err := os.Create(src)
 	if err != nil {
 		error(w, nil, err)
 		return

src/cmd/cgo/main.go

@@ -203,7 +203,7 @@ func main() {
 	// Use the beginning of the md5 of the input to disambiguate.
 	h := md5.New()
 	for _, input := range goFiles {
-		f, err := os.Open(input, os.O_RDONLY, 0)
+		f, err := os.Open(input)
 		if err != nil {
 			fatal("%s", err)
 		}

src/cmd/cgo/util.go

@@ -95,7 +95,7 @@ func isName(s string) bool {
 }
 
 func creat(name string) *os.File {
-	f, err := os.Open(name, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0666)
+	f, err := os.Create(name)
 	if err != nil {
 		fatal("%s", err)
 	}

src/cmd/godoc/codewalk.go

@@ -115,7 +115,7 @@ func (st *Codestep) String() string {
 
 // loadCodewalk reads a codewalk from the named XML file.
 func loadCodewalk(file string) (*Codewalk, os.Error) {
-	f, err := os.Open(file, os.O_RDONLY, 0)
+	f, err := os.Open(file)
 	if err != nil {
 		return nil, err
 	}

src/cmd/godoc/index.go

@@ -624,7 +624,7 @@ func pkgName(filename string) string {
 // failed (that is, if the file was not added), it returns file == nil.
 func (x *Indexer) addFile(filename string, goFile bool) (file *token.File, ast *ast.File) {
 	// open file
-	f, err := os.Open(filename, os.O_RDONLY, 0)
+	f, err := os.Open(filename)
 	if err != nil {
 		return
 	}

src/cmd/godoc/utils.go

@@ -155,7 +155,7 @@ func isTextFile(filename string) bool {
 
 	// the extension is not known; read an initial chunk
 	// of the file and check if it looks like text
-	f, err := os.Open(filename, os.O_RDONLY, 0)
+	f, err := os.Open(filename)
 	if err != nil {
 		return false
 	}

src/cmd/gofix/Makefile

@@ -9,6 +9,7 @@ GOFILES=\
 	fix.go\
 	netdial.go\
 	main.go\
+	osopen.go\
 	httpserver.go\
 	procattr.go\
 

src/cmd/gofix/main.go

@@ -93,7 +93,7 @@ func processFile(filename string, useStdin bool) os.Error {
 	if useStdin {
 		f = os.Stdin
 	} else {
-		f, err = os.Open(filename, os.O_RDONLY, 0)
+		f, err = os.Open(filename)
 		if err != nil {
 			return err
 		}

src/cmd/gofix/osopen.go

@@ -0,0 +1,109 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"go/ast"
+)
+
+var osopenFix = fix{
+	"osopen",
+	osopen,
+	`Adapt os.Open calls to new, easier API and rename O_CREAT O_CREATE.
+
+	http://codereview.appspot.com/4357052
+`,
+}
+
+func init() {
+	register(osopenFix)
+}
+
+func osopen(f *ast.File) bool {
+	if !imports(f, "os") {
+		return false
+	}
+
+	fixed := false
+	rewrite(f, func(n interface{}) {
+		// Rename O_CREAT to O_CREATE.
+		if expr, ok := n.(ast.Expr); ok && isPkgDot(expr, "os", "O_CREAT") {
+			expr.(*ast.SelectorExpr).Sel.Name = "O_CREATE"
+			return
+		}
+
+		// Fix up calls to Open.
+		call, ok := n.(*ast.CallExpr)
+		if !ok || len(call.Args) != 3 {
+			return
+		}
+		if !isPkgDot(call.Fun, "os", "Open") {
+			return
+		}
+		sel := call.Fun.(*ast.SelectorExpr)
+		args := call.Args
+		// os.Open(a, os.O_RDONLY, c) -> os.Open(a)
+		if isPkgDot(args[1], "os", "O_RDONLY") || isPkgDot(args[1], "syscall", "O_RDONLY") {
+			call.Args = call.Args[0:1]
+			fixed = true
+			return
+		}
+		// os.Open(a, createlike_flags, c) -> os.Create(a, c)
+		if isCreateFlag(args[1]) {
+			sel.Sel.Name = "Create"
+			if !isSimplePerm(args[2]) {
+				warn(sel.Pos(), "rewrote os.Open to os.Create with permission not 0666")
+			}
+			call.Args = args[0:1]
+			fixed = true
+			return
+		}
+		// Fallback: os.Open(a, b, c) -> os.OpenFile(a, b, c)
+		sel.Sel.Name = "OpenFile"
+		fixed = true
+	})
+	return fixed
+}
+
+func isCreateFlag(flag ast.Expr) bool {
+	foundCreate := false
+	foundTrunc := false
+	// OR'ing of flags: is O_CREATE on?  + or | would be fine; we just look for os.O_CREATE
+	// and don't worry about the actual opeator.
+	p := flag.Pos()
+	for {
+		lhs := flag
+		expr, isBinary := flag.(*ast.BinaryExpr)
+		if isBinary {
+			lhs = expr.Y
+		}
+		if isPkgDot(lhs, "os", "O_CREATE") {
+			foundCreate = true
+		}
+		if isPkgDot(lhs, "os", "O_TRUNC") {
+			foundTrunc = true
+		}
+		if !isBinary {
+			break
+		}
+		flag = expr.X
+	}
+	if foundCreate && !foundTrunc {
+		warn(p, "rewrote os.Open with O_CREATE but not O_TRUNC to os.Create")
+	}
+	return foundCreate
+}
+
+func isSimplePerm(perm ast.Expr) bool {
+	basicLit, ok := perm.(*ast.BasicLit)
+	if !ok {
+		return false
+	}
+	switch basicLit.Value {
+	case "0666":
+		return true
+	}
+	return false
+}

src/cmd/gofix/osopen_test.go

@@ -0,0 +1,53 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func init() {
+	addTestCases(osopenTests)
+}
+
+var osopenTests = []testCase{
+	{
+		Name: "osopen.0",
+		In: `package main
+
+import (
+	"os"
+)
+
+func f() {
+	os.OpenFile(a, b, c)
+	os.Open(a, os.O_RDONLY, 0)
+	os.Open(a, os.O_RDONLY, 0666)
+	os.Open(a, os.O_RDWR, 0)
+	os.Open(a, os.O_CREAT, 0666)
+	os.Open(a, os.O_CREAT|os.O_TRUNC, 0664)
+	os.Open(a, os.O_CREATE, 0666)
+	os.Open(a, os.O_CREATE|os.O_TRUNC, 0664)
+	os.Open(a, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+	_ = os.O_CREAT
+}
+`,
+		Out: `package main
+
+import (
+	"os"
+)
+
+func f() {
+	os.OpenFile(a, b, c)
+	os.Open(a)
+	os.Open(a)
+	os.OpenFile(a, os.O_RDWR, 0)
+	os.Create(a)
+	os.Create(a)
+	os.Create(a)
+	os.Create(a)
+	os.Create(a)
+	_ = os.O_CREATE
+}
+`,
+	},
+}

src/cmd/gofmt/gofmt.go

@@ -135,7 +135,7 @@ func processFile(f *os.File) os.Error {
 
 
 func processFileByName(filename string) os.Error {
-	file, err := os.Open(filename, os.O_RDONLY, 0)
+	file, err := os.Open(filename)
 	if err != nil {
 		return err
 	}
@@ -194,7 +194,7 @@ func gofmtMain() {
 	}
 
 	if *cpuprofile != "" {
-		f, err := os.Open(*cpuprofile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+		f, err := os.Create(*cpuprofile)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "creating cpu profile: %s\n", err)
 			exitCode = 2

src/cmd/goinstall/main.go

@@ -120,7 +120,7 @@ func logPackage(pkg string) {
 	if installedPkgs[pkg] {
 		return
 	}
-	fout, err := os.Open(logfile, os.O_WRONLY|os.O_APPEND|os.O_CREAT, 0644)
+	fout, err := os.Create(logfile)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s: %s\n", argv0, err)
 		return

src/cmd/goinstall/parse.go

@@ -39,7 +39,7 @@ type dirInfo struct {
 // The imports map keys are package paths imported by listed Go files,
 // and the values are the Go files importing the respective package paths.
 func scanDir(dir string, allowMain bool) (info *dirInfo, err os.Error) {
-	f, err := os.Open(dir, os.O_RDONLY, 0)
+	f, err := os.Open(dir)
 	if err != nil {
 		return nil, err
 	}

src/cmd/gotest/gotest.go

@@ -159,7 +159,7 @@ func getTestFileNames() {
 		}
 	}
 	for _, n := range names {
-		fd, err := os.Open(n, os.O_RDONLY, 0)
+		fd, err := os.Open(n)
 		if err != nil {
 			Fatalf("%s: %s", n, err)
 		}
@@ -313,7 +313,7 @@ func doRun(argv []string, returnStdout bool) string {
 
 // writeTestmainGo generates the test program to be compiled, "./_testmain.go".
 func writeTestmainGo() {
-	f, err := os.Open("_testmain.go", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+	f, err := os.Create("_testmain.go")
 	if err != nil {
 		Fatalf("can't create _testmain.go: %s", err)
 	}

src/cmd/gotype/gotype.go

@@ -130,7 +130,7 @@ func isGoFilename(filename string) bool {
 
 
 func processDirectory(dirname string) {
-	f, err := os.Open(dirname, os.O_RDONLY, 0)
+	f, err := os.Open(dirname)
 	if err != nil {
 		report(err)
 		return

src/cmd/goyacc/goyacc.go

@@ -1361,7 +1361,7 @@ func openup() {
 
 	foutput = nil
 	if vflag != "" {
-		foutput = create(vflag, 0666)
+		foutput = create(vflag)
 		if foutput == nil {
 			error("can't create file %v", vflag)
 		}
@@ -1371,7 +1371,7 @@ func openup() {
 	if oflag == "" {
 		oflag = "y.go"
 	}
-	ftable = create(oflag, 0666)
+	ftable = create(oflag)
 	if ftable == nil {
 		error("can't create file %v", oflag)
 	}
@@ -3036,7 +3036,7 @@ func write(f *bufio.Writer, b []byte, n int) int {
 }
 
 func open(s string) *bufio.Reader {
-	fi, err := os.Open(s, os.O_RDONLY, 0)
+	fi, err := os.Open(s)
 	if err != nil {
 		error("error opening %v: %v", s, err)
 	}
@@ -3044,12 +3044,12 @@ func open(s string) *bufio.Reader {
 	return bufio.NewReader(fi)
 }
 
-func create(s string, m uint32) *bufio.Writer {
-	fo, err := os.Open(s, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, m)
+func create(s string) *bufio.Writer {
+	fo, err := os.Create(s)
 	if err != nil {
-		error("error opening %v: %v", s, err)
+		error("error creating %v: %v", s, err)
 	}
-	//fmt.Printf("create %v mode %v\n", s, m);
+	//fmt.Printf("create %v mode %v\n", s);
 	return bufio.NewWriter(fo)
 }
 

src/cmd/goyacc/units.y

@@ -299,7 +299,7 @@ func main() {
 		file = flag.Arg(0)
 	}
 
-	f, err := os.Open(file, os.O_RDONLY, 0)
+	f, err := os.Open(file)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "error opening %v: %v\n", file, err)
 		os.Exit(1)

src/pkg/archive/tar/reader_test.go

@@ -113,7 +113,7 @@ var untarTests = []*untarTest{
 func TestReader(t *testing.T) {
 testLoop:
 	for i, test := range untarTests {
-		f, err := os.Open(test.file, os.O_RDONLY, 0444)
+		f, err := os.Open(test.file)
 		if err != nil {
 			t.Errorf("test %d: Unexpected error: %v", i, err)
 			continue
@@ -143,7 +143,7 @@ testLoop:
 }
 
 func TestPartialRead(t *testing.T) {
-	f, err := os.Open("testdata/gnu.tar", os.O_RDONLY, 0444)
+	f, err := os.Open("testdata/gnu.tar")
 	if err != nil {
 		t.Fatalf("Unexpected error: %v", err)
 	}
@@ -181,7 +181,7 @@ func TestPartialRead(t *testing.T) {
 
 func TestIncrementalRead(t *testing.T) {
 	test := gnuTarTest
-	f, err := os.Open(test.file, os.O_RDONLY, 0444)
+	f, err := os.Open(test.file)
 	if err != nil {
 		t.Fatalf("Unexpected error: %v", err)
 	}
@@ -235,7 +235,7 @@ func TestIncrementalRead(t *testing.T) {
 
 func TestNonSeekable(t *testing.T) {
 	test := gnuTarTest
-	f, err := os.Open(test.file, os.O_RDONLY, 0444)
+	f, err := os.Open(test.file)
 	if err != nil {
 		t.Fatalf("Unexpected error: %v", err)
 	}

src/pkg/archive/zip/reader.go

@@ -49,7 +49,7 @@ func (f *File) hasDataDescriptor() bool {
 
 // OpenReader will open the Zip file specified by name and return a Reader.
 func OpenReader(name string) (*Reader, os.Error) {
-	f, err := os.Open(name, os.O_RDONLY, 0644)
+	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}

src/pkg/compress/lzw/writer_test.go

@@ -21,7 +21,7 @@ var filenames = []string{
 // the given options yields equivalent bytes to the original file.
 func testFile(t *testing.T, fn string, order Order, litWidth int) {
 	// Read the file, as golden output.
-	golden, err := os.Open(fn, os.O_RDONLY, 0400)
+	golden, err := os.Open(fn)
 	if err != nil {
 		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err)
 		return
@@ -29,7 +29,7 @@ func testFile(t *testing.T, fn string, order Order, litWidth int) {
 	defer golden.Close()
 
 	// Read the file again, and push it through a pipe that compresses at the write end, and decompresses at the read end.
-	raw, err := os.Open(fn, os.O_RDONLY, 0400)
+	raw, err := os.Open(fn)
 	if err != nil {
 		t.Errorf("%s (order=%d litWidth=%d): %v", fn, order, litWidth, err)
 		return

src/pkg/compress/zlib/writer_test.go

@@ -20,7 +20,7 @@ var filenames = []string{
 // yields equivalent bytes to the original file.
 func testFileLevel(t *testing.T, fn string, level int) {
 	// Read the file, as golden output.
-	golden, err := os.Open(fn, os.O_RDONLY, 0444)
+	golden, err := os.Open(fn)
 	if err != nil {
 		t.Errorf("%s (level=%d): %v", fn, level, err)
 		return
@@ -28,7 +28,7 @@ func testFileLevel(t *testing.T, fn string, level int) {
 	defer golden.Close()
 
 	// Read the file again, and push it through a pipe that compresses at the write end, and decompresses at the read end.
-	raw, err := os.Open(fn, os.O_RDONLY, 0444)
+	raw, err := os.Open(fn)
 	if err != nil {
 		t.Errorf("%s (level=%d): %v", fn, level, err)
 		return

src/pkg/crypto/rand/rand_unix.go

@@ -32,7 +32,7 @@ func (r *devReader) Read(b []byte) (n int, err os.Error) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	if r.f == nil {
-		f, err := os.Open(r.name, os.O_RDONLY, 0)
+		f, err := os.Open(r.name)
 		if f == nil {
 			return 0, err
 		}

src/pkg/crypto/tls/generate_cert.go

@@ -50,7 +50,7 @@ func main() {
 		return
 	}
 
-	certOut, err := os.Open("cert.pem", os.O_WRONLY|os.O_CREAT, 0644)
+	certOut, err := os.Create("cert.pem")
 	if err != nil {
 		log.Fatalf("failed to open cert.pem for writing: %s", err)
 		return
@@ -59,7 +59,7 @@ func main() {
 	certOut.Close()
 	log.Print("written cert.pem\n")
 
-	keyOut, err := os.Open("key.pem", os.O_WRONLY|os.O_CREAT, 0600)
+	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREAT, 0600)
 	if err != nil {
 		log.Print("failed to open key.pem for writing:", err)
 		return

src/pkg/debug/elf/file.go

@@ -144,7 +144,7 @@ func (e *FormatError) String() string {
 
 // Open opens the named file using os.Open and prepares it for use as an ELF binary.
 func Open(name string) (*File, os.Error) {
-	f, err := os.Open(name, os.O_RDONLY, 0)
+	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}

src/pkg/debug/macho/file.go

@@ -159,7 +159,7 @@ func (e *FormatError) String() string {
 
 // Open opens the named file using os.Open and prepares it for use as a Mach-O binary.
 func Open(name string) (*File, os.Error) {
-	f, err := os.Open(name, os.O_RDONLY, 0)
+	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}

src/pkg/debug/pe/file.go

@@ -87,7 +87,7 @@ func (e *FormatError) String() string {
 
 // Open opens the named file using os.Open and prepares it for use as a PE binary.
 func Open(name string) (*File, os.Error) {
-	f, err := os.Open(name, os.O_RDONLY, 0)
+	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}

src/pkg/debug/proc/proc_linux.go

@@ -1184,7 +1184,7 @@ func (p *process) attachThread(tid int) (*thread, os.Error) {
 // attachAllThreads attaches to all threads in a process.
 func (p *process) attachAllThreads() os.Error {
 	taskPath := "/proc/" + strconv.Itoa(p.pid) + "/task"
-	taskDir, err := os.Open(taskPath, os.O_RDONLY, 0)
+	taskDir, err := os.Open(taskPath)
 	if err != nil {
 		return err
 	}

src/pkg/exec/exec.go

@@ -49,7 +49,7 @@ func modeToFiles(mode, fd int) (*os.File, *os.File, os.Error) {
 		if fd == 0 {
 			rw = os.O_RDONLY
 		}
-		f, err := os.Open(os.DevNull, rw, 0)
+		f, err := os.OpenFile(os.DevNull, rw, 0)
 		return f, nil, err
 	case PassThrough:
 		switch fd {

src/pkg/exp/draw/x11/auth.go

@@ -53,7 +53,7 @@ func readAuth(displayStr string) (name, data string, err os.Error) {
 		}
 		fn = home + "/.Xauthority"
 	}
-	r, err := os.Open(fn, os.O_RDONLY, 0444)
+	r, err := os.Open(fn)
 	if err != nil {
 		return
 	}

src/pkg/exp/ogle/cmd.go

@@ -170,7 +170,7 @@ func cmdLoad(args []byte) os.Error {
 	}
 
 	// Get symbols
-	f, err := os.Open(fname, os.O_RDONLY, 0)
+	f, err := os.Open(fname)
 	if err != nil {
 		tproc.Detach()
 		return err

src/pkg/go/parser/interface.go

@@ -183,7 +183,7 @@ func ParseFiles(fset *token.FileSet, filenames []string, mode uint) (pkgs map[st
 // error are returned.
 //
 func ParseDir(fset *token.FileSet, path string, filter func(*os.FileInfo) bool, mode uint) (map[string]*ast.Package, os.Error) {
-	fd, err := os.Open(path, os.O_RDONLY, 0)
+	fd, err := os.Open(path)
 	if err != nil {
 		return nil, err
 	}

src/pkg/gob/dump.go

@@ -12,7 +12,7 @@ func main() {
 	var err os.Error
 	file := os.Stdin
 	if len(os.Args) > 1 {
-		file, err = os.Open(os.Args[1], os.O_RDONLY, 0)
+		file, err = os.Open(os.Args[1])
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "dump: %s\n", err)
 			os.Exit(1)

src/pkg/html/parse_test.go

@@ -28,7 +28,7 @@ func pipeErr(err os.Error) io.Reader {
 }
 
 func readDat(filename string, c chan io.Reader) {
-	f, err := os.Open("testdata/webkit/"+filename, os.O_RDONLY, 0600)
+	f, err := os.Open("testdata/webkit/" + filename)
 	if err != nil {
 		c <- pipeErr(err)
 		return

src/pkg/http/fs.go

@@ -72,7 +72,7 @@ func serveFile(w ResponseWriter, r *Request, name string, redirect bool) {
 		return
 	}
 
-	f, err := os.Open(name, os.O_RDONLY, 0)
+	f, err := os.Open(name)
 	if err != nil {
 		// TODO expose actual error?
 		NotFound(w, r)
@@ -113,7 +113,7 @@ func serveFile(w ResponseWriter, r *Request, name string, redirect bool) {
 	// use contents of index.html for directory, if present
 	if d.IsDirectory() {
 		index := name + filepath.FromSlash(indexPage)
-		ff, err := os.Open(index, os.O_RDONLY, 0)
+		ff, err := os.Open(index)
 		if err == nil {
 			defer ff.Close()
 			dd, err := ff.Stat()

src/pkg/image/decode_test.go

@@ -34,7 +34,7 @@ var imageTests = []imageTest{
 }
 
 func decode(filename string) (image.Image, string, os.Error) {
-	f, err := os.Open(filename, os.O_RDONLY, 0400)
+	f, err := os.Open(filename)
 	if err != nil {
 		return nil, "", err
 	}

src/pkg/image/png/reader_test.go

@@ -41,7 +41,7 @@ var filenamesShort = []string{
 }
 
 func readPng(filename string) (image.Image, os.Error) {
-	f, err := os.Open(filename, os.O_RDONLY, 0444)
+	f, err := os.Open(filename)
 	if err != nil {
 		return nil, err
 	}
@@ -191,7 +191,7 @@ func TestReader(t *testing.T) {
 		defer piper.Close()
 
 		// Read the .sng file.
-		sf, err := os.Open("testdata/pngsuite/"+fn+".sng", os.O_RDONLY, 0444)
+		sf, err := os.Open("testdata/pngsuite/" + fn + ".sng")
 		if err != nil {
 			t.Error(fn, err)
 			continue

src/pkg/io/ioutil/ioutil.go

@@ -28,7 +28,7 @@ func ReadAll(r io.Reader) ([]byte, os.Error) {
 
 // ReadFile reads the file named by filename and returns the contents.
 func ReadFile(filename string) ([]byte, os.Error) {
-	f, err := os.Open(filename, os.O_RDONLY, 0)
+	f, err := os.Open(filename)
 	if err != nil {
 		return nil, err
 	}
@@ -52,7 +52,7 @@ func ReadFile(filename string) ([]byte, os.Error) {
 // If the file does not exist, WriteFile creates it with permissions perm;
 // otherwise WriteFile truncates it before writing.
 func WriteFile(filename string, data []byte, perm uint32) os.Error {
-	f, err := os.Open(filename, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, perm)
+	f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
 	if err != nil {
 		return err
 	}
@@ -74,7 +74,7 @@ func (f fileInfoList) Swap(i, j int)      { f[i], f[j] = f[j], f[i] }
 // ReadDir reads the directory named by dirname and returns
 // a list of sorted directory entries.
 func ReadDir(dirname string) ([]*os.FileInfo, os.Error) {
-	f, err := os.Open(dirname, os.O_RDONLY, 0)
+	f, err := os.Open(dirname)
 	if err != nil {
 		return nil, err
 	}

src/pkg/io/ioutil/tempfile.go

@@ -48,7 +48,7 @@ func TempFile(dir, prefix string) (f *os.File, err os.Error) {
 	nconflict := 0
 	for i := 0; i < 10000; i++ {
 		name := filepath.Join(dir, prefix+nextSuffix())
-		f, err = os.Open(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+		f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
 		if pe, ok := err.(*os.PathError); ok && pe.Error == os.EEXIST {
 			if nconflict++; nconflict > 10 {
 				rand = reseed()

src/pkg/mime/type.go

@@ -33,7 +33,7 @@ var mimeTypes = map[string]string{
 var mimeLock sync.RWMutex
 
 func loadMimeFile(filename string) {
-	f, err := os.Open(filename, os.O_RDONLY, 0666)
+	f, err := os.Open(filename)
 	if err != nil {
 		return
 	}

src/pkg/net/parse.go

@@ -63,7 +63,7 @@ func (f *file) readLine() (s string, ok bool) {
 }
 
 func open(name string) (*file, os.Error) {
-	fd, err := os.Open(name, os.O_RDONLY, 0)
+	fd, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}

src/pkg/net/parse_test.go

@@ -18,7 +18,7 @@ func TestReadLine(t *testing.T) {
 	}
 	filename := "/etc/services" // a nice big file
 
-	fd, err := os.Open(filename, os.O_RDONLY, 0)
+	fd, err := os.Open(filename)
 	if err != nil {
 		t.Fatalf("open %s: %v", filename, err)
 	}

src/pkg/os/env_plan9.go

@@ -17,7 +17,7 @@ func Getenverror(key string) (value string, err Error) {
 	if len(key) == 0 {
 		return "", EINVAL
 	}
-	f, e := Open("/env/"+key, O_RDONLY, 0)
+	f, e := Open("/env/" + key)
 	if iserror(e) {
 		return "", ENOENV
 	}
@@ -46,7 +46,7 @@ func Setenv(key, value string) Error {
 		return EINVAL
 	}
 
-	f, e := Open("/env/"+key, O_WRONLY|O_CREAT, 0666)
+	f, e := Create("/env/" + key)
 	if iserror(e) {
 		return e
 	}
@@ -66,7 +66,7 @@ func Clearenv() {
 func Environ() []string {
 	env := make([]string, 0, 100)
 
-	f, e := Open("/env", O_RDONLY, 0)
+	f, e := Open("/env")
 	if iserror(e) {
 		panic(e)
 	}

src/pkg/os/file.go

@@ -51,14 +51,13 @@ const (
 	O_RDWR     int = syscall.O_RDWR     // open the file read-write.
 	O_APPEND   int = syscall.O_APPEND   // append data to the file when writing.
 	O_ASYNC    int = syscall.O_ASYNC    // generate a signal when I/O is available.
-	O_CREAT    int = syscall.O_CREAT    // create a new file if none exists.
-	O_EXCL     int = syscall.O_EXCL     // used with O_CREAT, file must not exist
+	O_CREATE   int = syscall.O_CREAT    // create a new file if none exists.
+	O_EXCL     int = syscall.O_EXCL     // used with O_CREATE, file must not exist
 	O_NOCTTY   int = syscall.O_NOCTTY   // do not make file the controlling tty.
 	O_NONBLOCK int = syscall.O_NONBLOCK // open in non-blocking mode.
 	O_NDELAY   int = O_NONBLOCK         // synonym for O_NONBLOCK
 	O_SYNC     int = syscall.O_SYNC     // open for synchronous I/O.
 	O_TRUNC    int = syscall.O_TRUNC    // if possible, truncate file when opened.
-	O_CREATE   int = O_CREAT            // create a new file if none exists.
 )
 
 // Seek whence values.
@@ -215,3 +214,20 @@ func (f *File) Chdir() Error {
 	}
 	return nil
 }
+
+// Open opens the named file for reading.  If successful, methods on
+// the returned file can be used for reading; the associated file
+// descriptor has mode O_RDONLY.
+// It returns the File and an Error, if any.
+func Open(name string) (file *File, err Error) {
+	return OpenFile(name, O_RDONLY, 0)
+}
+
+// Create creates the named file mode 0666 (before umask), truncating
+// it if it already exists.  If successful, methods on the returned
+// File can be used for I/O; the associated file descriptor has mode
+// O_RDWR.
+// It returns the File and an Error, if any.
+func Create(name string) (file *File, err Error) {
+	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
+}

src/pkg/os/file_plan9.go

@@ -17,16 +17,18 @@ func epipecheck(file *File, e syscall.Error) {
 // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
 const DevNull = "/dev/null"
 
-// Open opens the named file with specified flag (O_RDONLY etc.) and perm.
-// If successful, methods on the returned File can be used for I/O.
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
 // It returns the File and an Error, if any.
-func Open(name string, flag int, perm uint32) (file *File, err Error) {
+func OpenFile(name string, flag int, perm uint32) (file *File, err Error) {
 	var fd int
 	var e syscall.Error
 
 	syscall.ForkLock.RLock()
-	if flag&O_CREAT == O_CREAT {
-		fd, e = syscall.Create(name, flag & ^O_CREAT, perm)
+	if flag&O_CREATE == O_CREATE {
+		fd, e = syscall.Create(name, flag & ^O_CREATE, perm)
 	} else {
 		fd, e = syscall.Open(name, flag)
 	}

src/pkg/os/file_unix.go

@@ -20,10 +20,12 @@ type dirInfo struct {
 // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
 const DevNull = "/dev/null"
 
-// Open opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.)
-// if applicable.  If successful, methods on the returned File can be used for I/O.
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
 // It returns the File and an Error, if any.
-func Open(name string, flag int, perm uint32) (file *File, err Error) {
+func OpenFile(name string, flag int, perm uint32) (file *File, err Error) {
 	r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, perm)
 	if e != 0 {
 		return nil, &PathError{"open", name, Errno(e)}

src/pkg/os/file_windows.go

@@ -46,10 +46,12 @@ func openDir(name string) (file *File, err Error) {
 	return f, nil
 }
 
-// Open opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.)
-// if applicable.  If successful, methods on the returned File can be used for I/O.
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
 // It returns the File and an Error, if any.
-func Open(name string, flag int, perm uint32) (file *File, err Error) {
+func OpenFile(name string, flag int, perm uint32) (file *File, err Error) {
 	// TODO(brainman): not sure about my logic of assuming it is dir first, then fall back to file
 	r, e := openDir(name)
 	if e == nil {
@@ -166,7 +168,7 @@ func (file *File) Readdir(count int) (fi []FileInfo, err Error) {
 // Truncate changes the size of the named file.
 // If the file is a symbolic link, it changes the size of the link's target.
 func Truncate(name string, size int64) Error {
-	f, e := Open(name, O_WRONLY|O_CREAT, 0666)
+	f, e := Open(name, O_WRONLY|O_CREATE, 0666)
 	if e != nil {
 		return e
 	}

src/pkg/os/getwd.go

@@ -54,7 +54,7 @@ func Getwd() (string, Error) {
 		if len(parent) >= 1024 { // Sanity check
 			return "", ENAMETOOLONG
 		}
-		fd, err := Open(parent, O_RDONLY, 0)
+		fd, err := Open(parent)
 		if err != nil {
 			return "", err
 		}

src/pkg/os/inotify/inotify_linux_test.go

@@ -51,7 +51,7 @@ func TestInotifyEvents(t *testing.T) {
 
 	// Create a file
 	// This should add at least one event to the inotify event queue
-	_, err = os.Open(testFile, os.O_WRONLY|os.O_CREAT, 0666)
+	_, err = os.OpenFile(testFile, os.O_WRONLY|os.O_CREATE, 0666)
 	if err != nil {
 		t.Fatalf("creating test file failed: %s", err)
 	}

src/pkg/os/os_test.go

@@ -60,7 +60,7 @@ var sysdir = func() (sd *sysDir) {
 }()
 
 func size(name string, t *testing.T) int64 {
-	file, err := Open(name, O_RDONLY, 0)
+	file, err := Open(name)
 	defer file.Close()
 	if err != nil {
 		t.Fatal("open failed:", err)
@@ -125,7 +125,7 @@ func TestStat(t *testing.T) {
 
 func TestFstat(t *testing.T) {
 	path := sfdir + "/" + sfname
-	file, err1 := Open(path, O_RDONLY, 0)
+	file, err1 := Open(path)
 	defer file.Close()
 	if err1 != nil {
 		t.Fatal("open failed:", err1)
@@ -159,7 +159,7 @@ func TestLstat(t *testing.T) {
 }
 
 func testReaddirnames(dir string, contents []string, t *testing.T) {
-	file, err := Open(dir, O_RDONLY, 0)
+	file, err := Open(dir)
 	defer file.Close()
 	if err != nil {
 		t.Fatalf("open %q failed: %v", dir, err)
@@ -188,7 +188,7 @@ func testReaddirnames(dir string, contents []string, t *testing.T) {
 }
 
 func testReaddir(dir string, contents []string, t *testing.T) {
-	file, err := Open(dir, O_RDONLY, 0)
+	file, err := Open(dir)
 	defer file.Close()
 	if err != nil {
 		t.Fatalf("open %q failed: %v", dir, err)
@@ -249,7 +249,7 @@ func TestReaddirnamesOneAtATime(t *testing.T) {
 	if syscall.OS == "windows" {
 		dir = Getenv("SystemRoot") + "\\system32"
 	}
-	file, err := Open(dir, O_RDONLY, 0)
+	file, err := Open(dir)
 	defer file.Close()
 	if err != nil {
 		t.Fatalf("open %q failed: %v", dir, err)
@@ -258,7 +258,7 @@ func TestReaddirnamesOneAtATime(t *testing.T) {
 	if err1 != nil {
 		t.Fatalf("readdirnames %q failed: %v", dir, err1)
 	}
-	file1, err2 := Open(dir, O_RDONLY, 0)
+	file1, err2 := Open(dir)
 	if err2 != nil {
 		t.Fatalf("open %q failed: %v", dir, err2)
 	}
@@ -277,7 +277,7 @@ func TestHardLink(t *testing.T) {
 	}
 	from, to := "hardlinktestfrom", "hardlinktestto"
 	Remove(from) // Just in case.
-	file, err := Open(to, O_CREAT|O_WRONLY, 0666)
+	file, err := Create(to)
 	if err != nil {
 		t.Fatalf("open %q failed: %v", to, err)
 	}
@@ -310,7 +310,7 @@ func TestSymLink(t *testing.T) {
 	}
 	from, to := "symlinktestfrom", "symlinktestto"
 	Remove(from) // Just in case.
-	file, err := Open(to, O_CREAT|O_WRONLY, 0666)
+	file, err := Create(to)
 	if err != nil {
 		t.Fatalf("open %q failed: %v", to, err)
 	}
@@ -358,7 +358,7 @@ func TestSymLink(t *testing.T) {
 	if s != to {
 		t.Fatalf("after symlink %q != %q", s, to)
 	}
-	file, err = Open(from, O_RDONLY, 0)
+	file, err = Open(from)
 	if err != nil {
 		t.Fatalf("open %q failed: %v", from, err)
 	}
@@ -392,7 +392,7 @@ func TestLongSymlink(t *testing.T) {
 func TestRename(t *testing.T) {
 	from, to := "renamefrom", "renameto"
 	Remove(to) // Just in case.
-	file, err := Open(from, O_CREAT|O_WRONLY, 0666)
+	file, err := Create(from)
 	if err != nil {
 		t.Fatalf("open %q failed: %v", to, err)
 	}
@@ -619,7 +619,7 @@ func TestChdirAndGetwd(t *testing.T) {
 	if syscall.OS == "windows" {
 		return
 	}
-	fd, err := Open(".", O_RDONLY, 0)
+	fd, err := Open(".")
 	if err != nil {
 		t.Fatalf("Open .: %s", err)
 	}
@@ -631,7 +631,7 @@ func TestChdirAndGetwd(t *testing.T) {
 			if mode == 0 {
 				err = Chdir(d)
 			} else {
-				fd1, err := Open(d, O_RDONLY, 0)
+				fd1, err := Open(d)
 				if err != nil {
 					t.Errorf("Open %s: %s", d, err)
 					continue
@@ -740,7 +740,7 @@ var openErrorTests = []openErrorTest{
 
 func TestOpenError(t *testing.T) {
 	for _, tt := range openErrorTests {
-		f, err := Open(tt.path, tt.mode, 0)
+		f, err := OpenFile(tt.path, tt.mode, 0)
 		if err == nil {
 			t.Errorf("Open(%q, %d) succeeded", tt.path, tt.mode)
 			f.Close()
@@ -846,7 +846,7 @@ func TestWriteAt(t *testing.T) {
 }
 
 func writeFile(t *testing.T, fname string, flag int, text string) string {
-	f, err := Open(fname, flag, 0666)
+	f, err := OpenFile(fname, flag, 0666)
 	if err != nil {
 		t.Fatalf("Open: %v", err)
 	}
@@ -865,7 +865,7 @@ func writeFile(t *testing.T, fname string, flag int, text string) string {
 func TestAppend(t *testing.T) {
 	const f = "append.txt"
 	defer Remove(f)
-	s := writeFile(t, f, O_CREAT|O_TRUNC|O_RDWR, "new")
+	s := writeFile(t, f, O_CREATE|O_TRUNC|O_RDWR, "new")
 	if s != "new" {
 		t.Fatalf("writeFile: have %q want %q", s, "new")
 	}

src/pkg/os/path.go

@@ -80,7 +80,7 @@ func RemoveAll(path string) Error {
 	}
 
 	// Directory.
-	fd, err := Open(path, O_RDONLY, 0)
+	fd, err := Open(path)
 	if err != nil {
 		return err
 	}

src/pkg/os/path_test.go

@@ -29,7 +29,7 @@ func TestMkdirAll(t *testing.T) {
 
 	// Make file.
 	fpath := path + "/file"
-	_, err = Open(fpath, O_WRONLY|O_CREAT, 0666)
+	_, err = Create(fpath)
 	if err != nil {
 		t.Fatalf("create %q: %s", fpath, err)
 	}
@@ -72,7 +72,7 @@ func TestRemoveAll(t *testing.T) {
 	if err := MkdirAll(path, 0777); err != nil {
 		t.Fatalf("MkdirAll %q: %s", path, err)
 	}
-	fd, err := Open(fpath, O_WRONLY|O_CREAT, 0666)
+	fd, err := Create(fpath)
 	if err != nil {
 		t.Fatalf("create %q: %s", fpath, err)
 	}
@@ -88,12 +88,12 @@ func TestRemoveAll(t *testing.T) {
 	if err = MkdirAll(dpath, 0777); err != nil {
 		t.Fatalf("MkdirAll %q: %s", dpath, err)
 	}
-	fd, err = Open(fpath, O_WRONLY|O_CREAT, 0666)
+	fd, err = Create(fpath)
 	if err != nil {
 		t.Fatalf("create %q: %s", fpath, err)
 	}
 	fd.Close()
-	fd, err = Open(dpath+"/file", O_WRONLY|O_CREAT, 0666)
+	fd, err = Create(dpath + "/file")
 	if err != nil {
 		t.Fatalf("create %q: %s", fpath, err)
 	}
@@ -121,7 +121,7 @@ func TestRemoveAll(t *testing.T) {
 		}
 
 		for _, s := range []string{fpath, dpath + "/file1", path + "/zzz"} {
-			fd, err = Open(s, O_WRONLY|O_CREAT, 0666)
+			fd, err = Create(s)
 			if err != nil {
 				t.Fatalf("create %q: %s", s, err)
 			}

src/pkg/os/sys_linux.go

@@ -9,7 +9,7 @@ package os
 
 // Hostname returns the host name reported by the kernel.
 func Hostname() (name string, err Error) {
-	f, err := Open("/proc/sys/kernel/hostname", O_RDONLY, 0)
+	f, err := Open("/proc/sys/kernel/hostname")
 	if err != nil {
 		return "", err
 	}

src/pkg/os/sys_plan9.go

@@ -8,7 +8,7 @@ package os
 
 
 func Hostname() (name string, err Error) {
-	f, err := Open("#c/sysname", O_RDONLY, 0)
+	f, err := Open("#c/sysname")
 	if err != nil {
 		return "", err
 	}

src/pkg/path/filepath/match.go

@@ -263,7 +263,7 @@ func glob(dir, pattern string, matches []string) (m []string, e os.Error) {
 	if !fi.IsDirectory() {
 		return
 	}
-	d, err := os.Open(dir, os.O_RDONLY, 0666)
+	d, err := os.Open(dir)
 	if err != nil {
 		return
 	}

src/pkg/path/filepath/path.go

@@ -280,7 +280,7 @@ func walk(path string, f *os.FileInfo, v Visitor, errors chan<- os.Error) {
 // a list of sorted directory entries.
 // Copied from io/ioutil to avoid the circular import.
 func readDir(dirname string) ([]*os.FileInfo, os.Error) {
-	f, err := os.Open(dirname, os.O_RDONLY, 0)
+	f, err := os.Open(dirname)
 	if err != nil {
 		return nil, err
 	}

src/pkg/path/filepath/path_test.go

@@ -249,7 +249,7 @@ func walkTree(n *Node, path string, f func(path string, n *Node)) {
 func makeTree(t *testing.T) {
 	walkTree(tree, tree.name, func(path string, n *Node) {
 		if n.entries == nil {
-			fd, err := os.Open(path, os.O_CREAT, 0660)
+			fd, err := os.Create(path)
 			if err != nil {
 				t.Errorf("makeTree: %v", err)
 			}

src/pkg/strconv/fp_test.go

@@ -94,7 +94,7 @@ func myatof32(s string) (f float32, ok bool) {
 }
 
 func TestFp(t *testing.T) {
-	f, err := os.Open("testfp.txt", os.O_RDONLY, 0)
+	f, err := os.Open("testfp.txt")
 	if err != nil {
 		t.Fatal("testfp: open testfp.txt:", err.String())
 	}

src/pkg/testing/testing.go

@@ -212,7 +212,7 @@ func before() {
 		runtime.MemProfileRate = *memProfileRate
 	}
 	if *cpuProfile != "" {
-		f, err := os.Open(*cpuProfile, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0666)
+		f, err := os.Create(*cpuProfile)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "testing: %s", err)
 			return
@@ -233,7 +233,7 @@ func after() {
 		pprof.StopCPUProfile() // flushes profile to disk
 	}
 	if *memProfile != "" {
-		f, err := os.Open(*memProfile, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0666)
+		f, err := os.Create(*memProfile)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "testing: %s", err)
 			return