sys: add support for NetBSD getvfsstat

NetBSD replaced the getfsstat interface with getvfsstat in NetBSD 3.0.

Add a test for it.

With help from Benny Siegert and Ian Lance Taylor.

Change-Id: I115ae48c287cc32181006e9e8f7c15851e7e36c0
Reviewed-on: https://go-review.googlesource.com/c/sys/+/550476
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Benny Siegert <bsiegert@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

unix/getvfsstat_test.go

diff --git a/unix/getvfsstat_test.go b/unix/getvfsstat_test.go
new file mode 100644
index 0000000..30c963a
--- /dev/null
+++ b/unix/getvfsstat_test.go
@@ -0,0 +1,47 @@
+// Copyright 2023 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 netbsd
+
+package unix_test
+
+import (
+	"os/exec"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestGetvfsstat(t *testing.T) {
+	n, err := unix.Getvfsstat(nil, unix.MNT_NOWAIT)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	data := make([]unix.Statvfs_t, n)
+	n2, err := unix.Getvfsstat(data, unix.MNT_NOWAIT)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != n2 {
+		t.Errorf("Getvfsstat(nil) = %d, but subsequent Getvfsstat(slice) = %d", n, n2)
+	}
+	for i, stat := range data {
+		if stat == (unix.Statvfs_t{}) {
+			t.Errorf("index %v is an empty Statvfs_t struct", i)
+		}
+		t.Logf("%s on %s", unix.ByteSliceToString(stat.Mntfromname[:]), unix.ByteSliceToString(stat.Mntonname[:]))
+	}
+	if t.Failed() {
+		for i, stat := range data[:n2] {
+			t.Logf("data[%v] = %+v", i, stat)
+		}
+		mount, err := exec.Command("mount").CombinedOutput()
+		if err != nil {
+			t.Logf("mount: %v\n%s", err, mount)
+		} else {
+			t.Logf("mount: %s", mount)
+		}
+	}
+}

unix/syscall_netbsd.go

diff --git a/unix/syscall_netbsd.go b/unix/syscall_netbsd.go
index 8816209..34a4676 100644
--- a/unix/syscall_netbsd.go
+++ b/unix/syscall_netbsd.go
@@ -248,6 +248,23 @@
 	return Statvfs1(path, buf, ST_WAIT)
 }
 
+func Getvfsstat(buf []Statvfs_t, flags int) (n int, err error) {
+	var (
+		_p0     unsafe.Pointer
+		bufsize uintptr
+	)
+	if len(buf) > 0 {
+		_p0 = unsafe.Pointer(&buf[0])
+		bufsize = unsafe.Sizeof(Statvfs_t{}) * uintptr(len(buf))
+	}
+	r0, _, e1 := Syscall(SYS_GETVFSSTAT, uintptr(_p0), bufsize, uintptr(flags))
+	n = int(r0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
 /*
  * Exposed directly
  */