unix: add support for zos/s390x

This adds sys/unix support for zos/s390x.
These changes should not affect other platforms.

Fixes golang/go#43230

Change-Id: If1c1d9df134fbc44f95ca1b214e836508696da93
Reviewed-on: https://go-review.googlesource.com/c/sys/+/275992
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/fstatfs_zos_test.go

@@ -0,0 +1,73 @@
+// Copyright 2020 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.
+
+//go:build zos && s390x
+// +build zos,s390x
+
+package unix_test
+
+import (
+	"os"
+	"testing"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestFstatfs(t *testing.T) {
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	file, err := os.Open(wd)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	//Query Statfs_t and Statvfs_t from wd, check content
+	var stat unix.Statfs_t
+	err = unix.Fstatfs(int(file.Fd()), &stat)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var stat_v unix.Statvfs_t
+	err = unix.Fstatvfs(int(file.Fd()), &stat_v)
+	if stat.Bsize != stat_v.Bsize ||
+		stat.Blocks != stat_v.Blocks ||
+		stat.Bfree != stat_v.Bfree ||
+		stat.Bavail != stat_v.Bavail ||
+		stat.Files != stat_v.Files ||
+		stat.Ffree != stat_v.Ffree ||
+		stat.Fsid != stat_v.Fsid ||
+		stat.Namelen != stat_v.Namemax ||
+		stat.Frsize != stat_v.Frsize ||
+		stat.Flags != stat_v.Flag {
+		t.Errorf("Mismatching fields in Statfs_t and Statvfs_t.\nStatfs_t = %+v\nStatvfs_t = %+v", stat, stat_v)
+	}
+
+	//Initialize W_Mntent, find corresponding device and check filesystem type
+	var mnt_ent_buffer struct {
+		header       unix.W_Mnth
+		filesys_info [128]unix.W_Mntent
+	}
+	var buffer_size int = int(unsafe.Sizeof(mnt_ent_buffer))
+	var fs_count int = -1
+	for fs_count < 0 {
+		fs_count, err = unix.W_Getmntent((*byte)(unsafe.Pointer(&mnt_ent_buffer)), buffer_size)
+		if err != nil {
+			t.Fatal(err)
+		}
+		for i := 0; i < fs_count; i++ {
+			if stat.Fsid == uint64(mnt_ent_buffer.filesys_info[i].Dev) {
+				correct_type := uint32(mnt_ent_buffer.filesys_info[i].Fstname[0])
+				if stat.Type != correct_type {
+					t.Errorf("File system type is 0x%x. Should be 0x%x instead", stat.Type, correct_type)
+				}
+				return
+			}
+		}
+	}
+
+}