os: add ModeCharDevice

This should make conversion from Unix mode
to os.FileMode and back not lossy.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/5531052

src/pkg/os/stat_darwin.go

@@ -24,8 +24,10 @@ func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
 	}
 	fs.mode = FileMode(st.Mode & 0777)
 	switch st.Mode & syscall.S_IFMT {
-	case syscall.S_IFBLK, syscall.S_IFCHR, syscall.S_IFWHT:
+	case syscall.S_IFBLK, syscall.S_IFWHT:
 		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
 	case syscall.S_IFDIR:
 		fs.mode |= ModeDir
 	case syscall.S_IFIFO:

src/pkg/os/stat_freebsd.go

@@ -24,8 +24,10 @@ func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
 	}
 	fs.mode = FileMode(st.Mode & 0777)
 	switch st.Mode & syscall.S_IFMT {
-	case syscall.S_IFBLK, syscall.S_IFCHR:
+	case syscall.S_IFBLK:
 		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
 	case syscall.S_IFDIR:
 		fs.mode |= ModeDir
 	case syscall.S_IFIFO:

src/pkg/os/stat_linux.go

@@ -24,8 +24,10 @@ func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
 	}
 	fs.mode = FileMode(st.Mode & 0777)
 	switch st.Mode & syscall.S_IFMT {
-	case syscall.S_IFBLK, syscall.S_IFCHR:
+	case syscall.S_IFBLK:
 		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
 	case syscall.S_IFDIR:
 		fs.mode |= ModeDir
 	case syscall.S_IFIFO:

src/pkg/os/stat_netbsd.go

@@ -24,8 +24,10 @@ func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
 	}
 	fs.mode = FileMode(st.Mode & 0777)
 	switch st.Mode & syscall.S_IFMT {
-	case syscall.S_IFBLK, syscall.S_IFCHR:
+	case syscall.S_IFBLK:
 		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
 	case syscall.S_IFDIR:
 		fs.mode |= ModeDir
 	case syscall.S_IFIFO:

src/pkg/os/stat_openbsd.go

@@ -24,8 +24,10 @@ func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
 	}
 	fs.mode = FileMode(st.Mode & 0777)
 	switch st.Mode & syscall.S_IFMT {
-	case syscall.S_IFBLK, syscall.S_IFCHR:
+	case syscall.S_IFBLK:
 		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
 	case syscall.S_IFDIR:
 		fs.mode |= ModeDir
 	case syscall.S_IFIFO:

src/pkg/os/types.go

@@ -30,19 +30,23 @@ type FileMode uint32
 
 // The defined file mode bits are the most significant bits of the FileMode.
 // The nine least-significant bits are the standard Unix rwxrwxrwx permissions.
+// The values of these bits should be considered part of the public API and
+// may be used in wire protocols or disk representations: they must not be
+// changed, although new bits might be added.
 const (
 	// The single letters are the abbreviations
 	// used by the String method's formatting.
-	ModeDir       FileMode = 1 << (32 - 1 - iota) // d: is a directory
-	ModeAppend                                    // a: append-only
-	ModeExclusive                                 // l: exclusive use
-	ModeTemporary                                 // t: temporary file (not backed up)
-	ModeSymlink                                   // L: symbolic link
-	ModeDevice                                    // D: device file
-	ModeNamedPipe                                 // p: named pipe (FIFO)
-	ModeSocket                                    // S: Unix domain socket
-	ModeSetuid                                    // u: setuid
-	ModeSetgid                                    // g: setgid
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // t: temporary file (not backed up)
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
 
 	// Mask for the type bits. For regular files, none will be set.
 	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice
@@ -51,7 +55,7 @@ const (
 )
 
 func (m FileMode) String() string {
-	const str = "daltLDpSug"
+	const str = "daltLDpSugc"
 	var buf [20]byte
 	w := 0
 	for i, c := range str {