os: new FileInfo, FileMode types + update tree

R=golang-dev, r, r, gri, bradfitz, iant, iant, nigeltao, n13m3y3r
CC=golang-dev
https://golang.org/cl/5416060
diff --git a/src/pkg/os/os_unix_test.go b/src/pkg/os/os_unix_test.go
new file mode 100644
index 0000000..3109a81
--- /dev/null
+++ b/src/pkg/os/os_unix_test.go
@@ -0,0 +1,75 @@
+// Copyright 2009 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.
+
+// +build darwin freebsd linux openbsd
+
+package os_test
+
+import (
+	. "os"
+	"syscall"
+	"testing"
+)
+
+func checkUidGid(t *testing.T, path string, uid, gid int) {
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for uid/gid %d/%d): %s", path, uid, gid, err)
+	}
+	sys := dir.(*FileStat).Sys.(*syscall.Stat_t)
+	if int(sys.Uid) != uid {
+		t.Errorf("Stat %q: uid %d want %d", path, sys.Uid, uid)
+	}
+	if int(sys.Gid) != gid {
+		t.Errorf("Stat %q: gid %d want %d", path, sys.Gid, gid)
+	}
+}
+
+func TestChown(t *testing.T) {
+	// Chown is not supported under windows or Plan 9.
+	// Plan9 provides a native ChownPlan9 version instead.
+	if syscall.OS == "windows" || syscall.OS == "plan9" {
+		return
+	}
+	// Use TempDir() to make sure we're on a local file system,
+	// so that the group ids returned by Getgroups will be allowed
+	// on the file.  On NFS, the Getgroups groups are
+	// basically useless.
+	f := newFile("TestChown", t)
+	defer Remove(f.Name())
+	defer f.Close()
+	dir, err := f.Stat()
+	if err != nil {
+		t.Fatalf("stat %s: %s", f.Name(), err)
+	}
+
+	// Can't change uid unless root, but can try
+	// changing the group id.  First try our current group.
+	gid := Getgid()
+	t.Log("gid:", gid)
+	if err = Chown(f.Name(), -1, gid); err != nil {
+		t.Fatalf("chown %s -1 %d: %s", f.Name(), gid, err)
+	}
+	sys := dir.(*FileStat).Sys.(*syscall.Stat_t)
+	checkUidGid(t, f.Name(), int(sys.Uid), gid)
+
+	// Then try all the auxiliary groups.
+	groups, err := Getgroups()
+	if err != nil {
+		t.Fatalf("getgroups: %s", err)
+	}
+	t.Log("groups: ", groups)
+	for _, g := range groups {
+		if err = Chown(f.Name(), -1, g); err != nil {
+			t.Fatalf("chown %s -1 %d: %s", f.Name(), g, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), g)
+
+		// change back to gid to test fd.Chown
+		if err = f.Chown(-1, gid); err != nil {
+			t.Fatalf("fchown %s -1 %d: %s", f.Name(), gid, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), gid)
+	}
+}