cleanup: move pkg/ to internal/

The internal/ directory in Go has a special meaning, and indicates that
those packages are not meant for external consumption. Ceph-CSI does
provide public APIs for other projects to consume. There is no plan to
keep the API of the internally used packages stable.

Closes: #903
Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/util/pidlimit.go

@@ -0,0 +1,121 @@
+/*
+Copyright 2019 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	procCgroup    = "/proc/self/cgroup"
+	sysPidsMaxFmt = "/sys/fs/cgroup/pids%s/pids.max"
+)
+
+// return the cgouprs "pids.max" file of the current process
+//
+// find the line containing the pids group from the /proc/self/cgroup file
+// $ grep 'pids' /proc/self/cgroup
+// 7:pids:/kubepods.slice/kubepods-besteffort.slice/....scope
+// $ cat /sys/fs/cgroup/pids + *.scope + /pids.max
+func getCgroupPidsFile() (string, error) {
+	cgroup, err := os.Open(procCgroup)
+	if err != nil {
+		return "", err
+	}
+	defer cgroup.Close()
+
+	scanner := bufio.NewScanner(cgroup)
+	var slice string
+	for scanner.Scan() {
+		parts := strings.Split(scanner.Text(), ":")
+		if parts == nil || len(parts) < 3 {
+			continue
+		}
+		if parts[1] == "pids" {
+			slice = parts[2]
+			break
+		}
+	}
+	if slice == "" {
+		return "", fmt.Errorf("could not find a cgroup for 'pids'")
+	}
+
+	pidsMax := fmt.Sprintf(sysPidsMaxFmt, slice)
+	return pidsMax, nil
+}
+
+// GetPIDLimit returns the current PID limit, or an error. A value of -1
+// translates to "max".
+func GetPIDLimit() (int, error) {
+	pidsMax, err := getCgroupPidsFile()
+	if err != nil {
+		return 0, err
+	}
+
+	f, err := os.Open(pidsMax) // #nosec - intended reading from /sys/...
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+
+	maxPidsStr, err := bufio.NewReader(f).ReadString('\n')
+	if err != nil && err != io.EOF {
+		return 0, err
+	}
+	maxPidsStr = strings.TrimRight(maxPidsStr, "\n")
+
+	maxPids := -1
+	if maxPidsStr != "max" {
+		maxPids, err = strconv.Atoi(maxPidsStr)
+		if err != nil {
+			return 0, err
+		}
+	}
+	return maxPids, nil
+}
+
+// SetPIDLimit configures the given PID limit for the current process. A value
+// of -1 translates to "max".
+func SetPIDLimit(limit int) error {
+	limitStr := "max"
+	if limit != -1 {
+		limitStr = fmt.Sprintf("%d", limit)
+	}
+
+	pidsMax, err := getCgroupPidsFile()
+	if err != nil {
+		return err
+	}
+
+	f, err := os.Create(pidsMax)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = f.WriteString(limitStr)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}