unix: add Illumos statvfs(2) syscall

Reference: https://www.illumos.org/man/2/statvfs

Change-Id: If7af43da35b3204f5069a48eb08426a145544008
Reviewed-on: https://go-review.googlesource.com/43490
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_solaris_test.go

@@ -0,0 +1,34 @@
+// 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.
+
+// +build solaris
+
+package unix_test
+
+import (
+	"os/exec"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestStatvfs(t *testing.T) {
+	if err := unix.Statvfs("", nil); err == nil {
+		t.Fatal(`Statvfs("") expected failure`)
+	}
+
+	statvfs := unix.Statvfs_t{}
+	if err := unix.Statvfs("/", &statvfs); err != nil {
+		t.Errorf(`Statvfs("/") failed: %v`, err)
+	}
+
+	if t.Failed() {
+		mount, err := exec.Command("mount").CombinedOutput()
+		if err != nil {
+			t.Logf("mount: %v\n%s", err, mount)
+		} else {
+			t.Logf("mount: %s", mount)
+		}
+	}
+}