From 38c589042815e09ce3bda631f3e244f952ed1721 Mon Sep 17 00:00:00 2001
From: Dominik Honnef <dominik@honnef.co>
Date: Sat, 31 Dec 2016 07:23:55 +0100
Subject: [PATCH] Reuse devinfo struct

The devstat API expects us to reuse one devinfo for many invocations of
devstat_getstats. In particular, it allocates and resizes memory
referenced by devinfo.
---
 collector/devstat_freebsd.c  |  5 ++---
 collector/devstat_freebsd.go | 10 +++++++++-
 collector/devstat_freebsd.h  |  2 +-
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/collector/devstat_freebsd.c b/collector/devstat_freebsd.c
index 80a24e41..c3352e2c 100644
--- a/collector/devstat_freebsd.c
+++ b/collector/devstat_freebsd.c
@@ -10,10 +10,9 @@
 #include <devstat_freebsd.h>
 
 
-int _get_stats(Stats **stats) {
+int _get_stats(struct devinfo *info, Stats **stats) {
 	struct statinfo current;
-	struct devinfo info = {};
-	current.dinfo = &info;
+	current.dinfo = info;
 
 	if (devstat_getdevs(NULL, &current) == -1) {
 		return -1;
diff --git a/collector/devstat_freebsd.go b/collector/devstat_freebsd.go
index 34bc53c8..79176026 100644
--- a/collector/devstat_freebsd.go
+++ b/collector/devstat_freebsd.go
@@ -18,6 +18,7 @@ package collector
 import (
 	"errors"
 	"fmt"
+	"sync"
 	"unsafe"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -32,6 +33,9 @@ const (
 )
 
 type devstatCollector struct {
+	mu      sync.Mutex
+	devinfo *C.struct_devinfo
+
 	bytes       typedDesc
 	bytes_total typedDesc
 	transfers   typedDesc
@@ -48,6 +52,7 @@ func init() {
 // Device stats.
 func NewDevstatCollector() (Collector, error) {
 	return &devstatCollector{
+		devinfo: &C.struct_devinfo{},
 		bytes: typedDesc{prometheus.NewDesc(
 			prometheus.BuildFQName(Namespace, devstatSubsystem, "bytes_total"),
 			"The total number of bytes in transactions.",
@@ -77,8 +82,11 @@ func NewDevstatCollector() (Collector, error) {
 }
 
 func (c *devstatCollector) Update(ch chan<- prometheus.Metric) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	var stats *C.Stats
-	n := C._get_stats(&stats)
+	n := C._get_stats(c.devinfo, &stats)
 	if n == -1 {
 		return errors.New("devstat_getdevs failed")
 	}
diff --git a/collector/devstat_freebsd.h b/collector/devstat_freebsd.h
index 87f09f0b..4ee1c62d 100644
--- a/collector/devstat_freebsd.h
+++ b/collector/devstat_freebsd.h
@@ -38,4 +38,4 @@ typedef struct {
 
 
 int _get_ndevs();
-int _get_stats(Stats **stats);
+int _get_stats(struct devinfo *info, Stats **stats);