unix: use sort.Search for sysctl lookup on OpenBSD

Use sort.Search to look up sysctl mib values from names instead of using
a hand-crafted binary search.

Also add a simple test to verify sysctl is still working after the
change.

Change-Id: I844840ac434a704b14c3166c3730daffabd2f347
Reviewed-on: https://go-review.googlesource.com/76930
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_bsd_test.go

@@ -60,3 +60,11 @@ func TestSysctlRaw(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestSysctlUint32(t *testing.T) {
+	maxproc, err := unix.SysctlUint32("kern.maxproc")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("kern.maxproc: %v", maxproc)
+}

unix/syscall_openbsd.go

@@ -13,6 +13,7 @@
 package unix
 
 import (
+	"sort"
 	"syscall"
 	"unsafe"
 )
@@ -32,22 +33,11 @@ type SockaddrDatalink struct {
 func Syscall9(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
 func nametomib(name string) (mib []_C_int, err error) {
-	// Perform lookup via a binary search
-	left := 0
-	right := len(sysctlMib) - 1
-	for {
-		idx := left + (right-left)/2
-		switch {
-		case name == sysctlMib[idx].ctlname:
-			return sysctlMib[idx].ctloid, nil
-		case name > sysctlMib[idx].ctlname:
-			left = idx + 1
-		default:
-			right = idx - 1
-		}
-		if left > right {
-			break
-		}
+	i := sort.Search(len(sysctlMib), func(i int) bool {
+		return sysctlMib[i].ctlname >= name
+	})
+	if i < len(sysctlMib) && sysctlMib[i].ctlname == name {
+		return sysctlMib[i].ctloid, nil
 	}
 	return nil, EINVAL
 }