Source: mountinfo.go in package github.com/prometheus/procfs

Copyright 2019 The Prometheus 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 procfs

import (
	"bufio"
	"bytes"
	"fmt"
	"strconv"
	"strings"

	"github.com/prometheus/procfs/internal/util"
)

A MountInfo is a type that describes the details, options for each mount, parsed from /proc/self/mountinfo. The fields described in each entry of /proc/self/mountinfo is described in the following man page. http://man7.org/linux/man-pages/man5/proc.5.html

Unique Id for the mount

The Id of the parent mount

The value of `st_dev` for the files on this FS

The pathname of the directory in the FS that forms the root for this mount

The pathname of the mount point relative to the root

Mount options

Zero or more optional fields

The Filesystem type

FS specific information or "none"

Superblock options

	SuperOptions map[string]string
}

Reads each line of the mountinfo file, and returns a list of formatted MountInfo structs.

func parseMountInfo(info []byte) ([]*MountInfo, error) {
	mounts := []*MountInfo{}
	scanner := bufio.NewScanner(bytes.NewReader(info))
	for scanner.Scan() {
		mountString := scanner.Text()
		parsedMounts, err := parseMountInfoString(mountString)
		if err != nil {
			return nil, err
		}
		mounts = append(mounts, parsedMounts)
	}

	err := scanner.Err()
	return mounts, err
}

Parses a mountinfo file line, and converts it to a MountInfo struct. An important check here is to see if the hyphen separator, as if it does not exist, it means that the line is malformed.

func parseMountInfoString(mountString string) (*MountInfo, error) {
	var err error

	mountInfo := strings.Split(mountString, " ")
	mountInfoLength := len(mountInfo)
	if mountInfoLength < 11 {
		return nil, fmt.Errorf("couldn't find enough fields in mount string: %s", mountString)
	}

	if mountInfo[mountInfoLength-4] != "-" {
		return nil, fmt.Errorf("couldn't find separator in expected field: %s", mountInfo[mountInfoLength-4])
	}

	mount := &MountInfo{
		MajorMinorVer:  mountInfo[2],
		Root:           mountInfo[3],
		MountPoint:     mountInfo[4],
		Options:        mountOptionsParser(mountInfo[5]),
		OptionalFields: nil,
		FSType:         mountInfo[mountInfoLength-3],
		Source:         mountInfo[mountInfoLength-2],
		SuperOptions:   mountOptionsParser(mountInfo[mountInfoLength-1]),
	}

	mount.MountId, err = strconv.Atoi(mountInfo[0])
	if err != nil {
		return nil, fmt.Errorf("failed to parse mount ID")
	}
	mount.ParentId, err = strconv.Atoi(mountInfo[1])
	if err != nil {
		return nil, fmt.Errorf("failed to parse parent ID")

Has optional fields, which is a space separated list of values. Example: shared:2 master:7

	if mountInfo[6] != "" {
		mount.OptionalFields, err = mountOptionsParseOptionalFields(mountInfo[6 : mountInfoLength-4])
		if err != nil {
			return nil, err
		}
	}
	return mount, nil
}

mountOptionsIsValidField checks a string against a valid list of optional fields keys.

func mountOptionsIsValidField(s string) bool {
	switch s {
	case
		"shared",
		"master",
		"propagate_from",
		"unbindable":
		return true
	}
	return false
}

mountOptionsParseOptionalFields parses a list of optional fields strings into a double map of strings.

func mountOptionsParseOptionalFields(o []string) (map[string]string, error) {
	optionalFields := make(map[string]string)
	for _, field := range o {
		optionSplit := strings.SplitN(field, ":", 2)
		value := ""
		if len(optionSplit) == 2 {
			value = optionSplit[1]
		}
		if mountOptionsIsValidField(optionSplit[0]) {
			optionalFields[optionSplit[0]] = value
		}
	}
	return optionalFields, nil
}

Parses the mount options, superblock options.

func mountOptionsParser(mountOptions string) map[string]string {
	opts := make(map[string]string)
	options := strings.Split(mountOptions, ",")
	for _, opt := range options {
		splitOption := strings.Split(opt, "=")
		if len(splitOption) < 2 {
			key := splitOption[0]
			opts[key] = ""
		} else {
			key, value := splitOption[0], splitOption[1]
			opts[key] = value
		}
	}
	return opts
}

Retrieves mountinfo information from `/proc/self/mountinfo`.

func GetMounts() ([]*MountInfo, error) {
	data, err := util.ReadFileNoStat("/proc/self/mountinfo")
	if err != nil {
		return nil, err
	}
	return parseMountInfo(data)
}

Retrieves mountinfo information from a processes' `/proc/<pid>/mountinfo`.

func GetProcMounts(pid int) ([]*MountInfo, error) {
	data, err := util.ReadFileNoStat(fmt.Sprintf("/proc/%d/mountinfo", pid))
	if err != nil {
		return nil, err
	}
	return parseMountInfo(data)