Revert "[utils] GetNumOfPossibleCpus: switch from custom, file based implementation to get_nprocs()"

This reverts commit 54e362e.

Author: belyalov

itest/utils_test.go

@@ -12,6 +12,7 @@ import (
 )
 
 func TestGetNumOfPossibleCpus(t *testing.T) {
-	cpus := goebpf.GetNumOfPossibleCpus()
+	cpus, err := goebpf.GetNumOfPossibleCpus()
+	assert.NoError(t, err)
 	assert.True(t, cpus > 0)
 }

map.go

@@ -422,7 +422,11 @@ func (m *EbpfMap) Create() error {
 
 	// Per-CPU maps require extra space to store values from ALL possible CPUs
 	if m.isPerCpu() {
-		m.valueRealSize = m.ValueSize * GetNumOfPossibleCpus()
+		numCpus, err := GetNumOfPossibleCpus()
+		if err != nil {
+			return err
+		}
+		m.valueRealSize = m.ValueSize * numCpus
 	} else {
 		m.valueRealSize = m.ValueSize
 	}

utils.go

@@ -13,18 +13,6 @@ package goebpf
 #include "bpf.h"
 #include "bpf_helpers.h"
 
-
-// Mac does not have "sys/sysinfo.h" header, so making dummy here
-#ifdef __APPLE__
-static int get_nprocs(void)
-{
-	return 0;
-}
-#else
-#include "sys/sysinfo.h"
-#endif
-
-
 static int ebpf_obj_pin(__u32 fd, const char *pathname,
 		void *log_buf, size_t log_size)
 {
@@ -117,7 +105,9 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"net"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -294,16 +284,49 @@ func closeFd(fd int) error {
 	return nil
 }
 
+// Helper to get number of possible system CPUs from string
+func parseNumOfPossibleCpus(data string) (int, error) {
+	eInvalid := errors.New("Unable to get # of possible CPUs: invalid file format")
+	// VM support: when machine has only one CPU input is "0"
+	if strings.TrimSpace(data) == "0" {
+		return 1, nil
+	}
+	// Otherwise input looks like:
+	// 0-14
+	// where 0 is first possible CPU and 14 is the last
+	items := strings.Split(strings.TrimSpace(data), "-")
+	if len(items) != 2 {
+		return 0, eInvalid
+	}
+	first, err := strconv.Atoi(items[0])
+	if err != nil || first != 0 {
+		return 0, eInvalid
+	}
+	second, err := strconv.Atoi(items[1])
+	if err != nil {
+		return 0, eInvalid
+	}
+
+	return second + 1, nil
+}
+
 // GetNumOfPossibleCpus returns number of CPU available to eBPF program
 // NOTE: this is not the same as runtime.NumCPU()
-func GetNumOfPossibleCpus() int {
+func GetNumOfPossibleCpus() (int, error) {
+	// Idea taken from
+	// https://elixir.bootlin.com/linux/latest/source/tools/testing/selftests/bpf/bpf_util.h#L10
+	// P.S. runtime.NumCPU() cannot be used since it returns number of logical CPUs
+	var err error
 
-	// Do syscall only once
 	getPossibleCpusOnce.Do(func() {
-		numPossibleCpus = int(C.get_nprocs())
+		var data []byte
+		data, err = ioutil.ReadFile("/sys/devices/system/cpu/possible")
+		if err == nil {
+			numPossibleCpus, err = parseNumOfPossibleCpus(string(data))
+		}
 	})
 
-	return numPossibleCpus
+	return numPossibleCpus, err
 }
 
 // ParseFlexibleIntegerLittleEndian converts flexible amount of bytes

utils_test.go

@@ -9,6 +9,38 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestParseNumOfPossibleCpus(t *testing.T) {
+	runs := map[string]int{
+		"0":       1,
+		"0-0":     1,
+		"0-1":     2,
+		"0-14":    15,
+		"0-1\r\n": 2,
+	}
+
+	for str, numExpected := range runs {
+		num, err := parseNumOfPossibleCpus(str)
+		assert.NoError(t, err)
+		assert.Equal(t, numExpected, num)
+	}
+
+	// Negative runs
+	runsNegative := []string{
+		"",
+		"1",
+		"1-1",
+		"1-",
+		"-1",
+		"\r\n",
+	}
+
+	for _, str := range runsNegative {
+		num, err := parseNumOfPossibleCpus(str)
+		assert.Error(t, err)
+		assert.Equal(t, 0, num)
+	}
+}
+
 // Negative test for closeFd()
 func TestCloseFd(t *testing.T) {
 	err := closeFd(1111) // Some non-existing fd