unix: add Major, Minor and Mkdev functions on Dragonfly

Add Major, Minor and Mkdev functions for converting devices numbers to
their major/minor components and vice versa.

The functions follow the behavior of the macros defined in DragonFlyBSD's
sys/types.h header. However, the parameter and return types are changed
to match the existing implementations of these functions.

Test the conversion macros with some well-known device numbers.

Updates golang/go#8106

Change-Id: I84c128dff3108821caaa75dcec620cf5bdb1f32d
Reviewed-on: https://go-review.googlesource.com/61630Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/dev_dragonfly.go

+// Copyright 2017 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.
+
+// Functions to access/create device major and minor numbers matching the
+// encoding used in Dragonfly's sys/types.h header.
+//
+// The information below is extracted and adapted from sys/types.h:
+//
+// Minor gives a cookie instead of an index since in order to avoid changing the
+// meanings of bits 0-15 or wasting time and space shifting bits 16-31 for
+// devices that don't use them.
+
+package unix
+
+// Major returns the major component of a DragonFlyBSD device number.
+func Major(dev uint64) uint32 {
+	return uint32((dev >> 8) & 0xff)
+}
+
+// Minor returns the minor component of a DragonFlyBSD device number.
+func Minor(dev uint64) uint32 {
+	return uint32(dev & 0xffff00ff)
+}
+
+// Mkdev returns a DragonFlyBSD device number generated from the given major and
+// minor components.
+func Mkdev(major, minor uint32) uint64 {
+	return uint64((major << 8) | minor)
+}

unix/dev_dragonfly_test.go

+// Copyright 2017 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 unix_test
+
+import (
+	"fmt"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestDevices(t *testing.T) {
+	testCases := []struct {
+		path  string
+		major uint32
+		minor uint32
+	}{
+		// Minor is a cookie instead of an index on DragonFlyBSD
+		{"/dev/null", 10, 0x00000002},
+		{"/dev/random", 10, 0x00000003},
+		{"/dev/urandom", 10, 0x00000004},
+		{"/dev/zero", 10, 0x0000000c},
+		{"/dev/bpf", 15, 0xffff00ff},
+	}
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("%s %v:%v", tc.path, tc.major, tc.minor), func(t *testing.T) {
+			var stat unix.Stat_t
+			err := unix.Stat(tc.path, &stat)
+			if err != nil {
+				t.Errorf("failed to stat device: %v", err)
+				return
+			}
+
+			dev := uint64(stat.Rdev)
+			if unix.Major(dev) != tc.major {
+				t.Errorf("for %s Major(%#x) == %d, want %d", tc.path, dev, unix.Major(dev), tc.major)
+			}
+			if unix.Minor(dev) != tc.minor {
+				t.Errorf("for %s Minor(%#x) == %d, want %d", tc.path, dev, unix.Minor(dev), tc.minor)
+			}
+			if unix.Mkdev(tc.major, tc.minor) != dev {
+				t.Errorf("for %s Mkdev(%d, %d) == %#x, want %#x", tc.path, tc.major, tc.minor, unix.Mkdev(tc.major, tc.minor), dev)
+			}
+		})
+	}
+}