buildlet: raise ulimit for NetBSD

The NetBSD 8 builders had a very low RLIMIT_DATA (even as root).
The builders don't run run.bash, which normally increases the ulimit.

So do it ourselves on start-up. Currently this is only on NetBSD.
Deployed and verified it works now.

Fixes golang/go#22871

Change-Id: I6ecb38b985ce27f0f29b36b55367eb1729be29c9
Reviewed-on: https://go-review.googlesource.com/79955
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

cmd/buildlet/buildlet.go

@@ -95,6 +95,7 @@ func defaultListenAddr() string {
 var (
 	osHalt                   func()
 	configureSerialLogOutput func()
+	setOSRlimit              func() error
 )
 
 func main() {
@@ -134,6 +135,13 @@ func main() {
 	case "openbsd", "freebsd", "netbsd":
 		makeBSDFilesystemFast()
 	}
+	if setOSRlimit != nil {
+		err := setOSRlimit()
+		if err != nil {
+			log.Fatalf("setOSRLimit: %v", err)
+		}
+		log.Printf("set OS rlimits.")
+	}
 
 	if *reverse != "" && *reverseType != "" {
 		log.Fatalf("can't specify both --reverse and --reverse-type")

cmd/buildlet/buildlet_netbsd.go

@@ -0,0 +1,27 @@
+// 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 main
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func init() {
+	setOSRlimit = setNetBSDRlimit
+}
+
+// See https://github.com/golang/go/issues/22871#issuecomment-346888363
+func setNetBSDRlimit() error {
+	limit := unix.Rlimit{
+		Cur: unix.RLIM_INFINITY,
+		Max: unix.RLIM_INFINITY,
+	}
+	if err := unix.Setrlimit(unix.RLIMIT_DATA, &limit); err != nil && os.Getuid() == 0 {
+		return err
+	}
+	return nil
+}