proc.go

// Copyright (c) 2018, Sylabs Inc. All rights reserved.
// This software is licensed under a 3-clause BSD license. Please consult the
// LICENSE.md file distributed with the sources of this project regarding your
// rights to use or distribute this software.

package proc

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

// HasFilesystem returns whether kernel support filesystem or not
func HasFilesystem(fs string) (bool, error) {
	p, err := os.Open("/proc/filesystems")
	if err != nil {
		return false, fmt.Errorf("can't open /proc/filesystems: %s", err)
	}
	defer p.Close()

	suffix := "\t" + fs
	scanner := bufio.NewScanner(p)
	for scanner.Scan() {
		if strings.HasSuffix(scanner.Text(), suffix) {
			return true, nil
		}
	}
	return false, nil
}

// ParseMountInfo parses mountinfo pointing to path and returns a map
// of parent mount points with associated child mount points
func ParseMountInfo(path string) (map[string][]string, error) {
	mp := make(map[string][]string)
	mountlist := make(map[string][]string)

	p, err := os.Open(path)
	if err != nil {
		return mp, fmt.Errorf("can't open %s: %s", path, err)
	}
	defer p.Close()

	scanner := bufio.NewScanner(p)
	for scanner.Scan() {
		fields := strings.Fields(scanner.Text())
		mountlist[fields[0]] = fields
	}
	for k := range mountlist {
		if i, ok := mountlist[mountlist[k][1]]; ok {
			if mountlist[k][4] != i[4] {
				mp[i[4]] = append(mp[i[4]], mountlist[k][4])
			}
		}
	}
	return mp, nil
}

// ExtractPid returns a pid extracted from path of type "/proc/1"
func ExtractPid(path string) (pid uint, err error) {
	n, err := fmt.Sscanf(path, "/proc/%d", &pid)
	if n != 1 {
		return 0, fmt.Errorf("can't extract PID from %s: %s", path, err)
	}
	return
}

// CountChilds returns the number of child processes for a given process id
func CountChilds(pid int) (int, error) {
	childs := 0

	parentProc := fmt.Sprintf("/proc/%d", pid)
	if _, err := os.Stat(parentProc); os.IsNotExist(err) {
		return 0, fmt.Errorf("pid %d doesn't exists", pid)
	}

	parentLine := fmt.Sprintf("PPid:\t%d", pid)
	pattern := filepath.Join("/proc", "[0-9]*")

	matches, _ := filepath.Glob(pattern)
	for _, path := range matches {
		r, err := os.Open(filepath.Join(path, "status"))
		if err != nil {
			continue
		}
		scanner := bufio.NewScanner(r)
		for scanner.Scan() {
			if scanner.Text() == parentLine {
				childs++
				break
			}
		}
		r.Close()
	}
	return childs, nil
}

// ReadIDMap reads uid_map or gid_map and returns both container ID
// and host ID
func ReadIDMap(path string) (uint32, uint32, error) {
	r, err := os.Open(path)
	if err != nil {
		return 0, 0, err
	}
	defer r.Close()

	scanner := bufio.NewScanner(r)
	scanner.Scan()
	fields := strings.Fields(scanner.Text())

	containerID, err := strconv.ParseUint(fields[0], 10, 32)
	if err != nil {
		return 0, 0, err
	}
	hostID, err := strconv.ParseUint(fields[1], 10, 32)
	if err != nil {
		return 0, 0, err
	}

	return uint32(containerID), uint32(hostID), nil
}