udevcheck.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"reflect"
	"sort"
	"strings"
	"time"
)

const baseDevPath = "/sys/devices"

//Device type for devices
// contains a, "obj" which is the path to the kernel file and "env" which is a
// mapping that contains information about the device
type Device struct {
	obj string
	env map[string]string
}

//RunWaitUdev wait on changes to devices (every 5 seconds)
func RunWaitUdev(changed chan<- bool) {
	devices, err := ExistingDevices("usb")
	if err != nil {
		fmt.Println(err)
	}
	for {
		time.Sleep(time.Second * 5)
		ndevices, err := ExistingDevices("usb")
		if err != nil {
			fmt.Println(err)
		}
		if !reflect.DeepEqual(devices, ndevices) {
			devchanged := len(devices) - len(ndevices)
			if devchanged > 0 {
				warnLog.Printf("%d devices removed\n", devchanged)
			} else {
				warnLog.Printf("%d devices added\n", devchanged*-1)
			}

			select {
			case changed <- true:
			default:
			}
			devices = ndevices
		}
	}
}

//ExistingDevices return all plugged devices matched by the matcher
// All uevent files inside /sys/devices is crawled to match right env values
func ExistingDevices(subsystem string) ([]Device, error) {
	devices := make([]Device, 0)
	err := filepath.Walk(baseDevPath, func(path string, info os.FileInfo, err error) error {

		if err != nil {
			return err
		}

		if info.IsDir() || info.Name() != "uevent" {
			return nil
		}

		env, err := getEventFromUEventFile(path)
		if err != nil {
			return err
		}

		kernelObject := filepath.Dir(path)

		// Append to env subsystem if existing
		subsys := filepath.Join(kernelObject, "subsystem")
		if link, err := os.Readlink(subsys); err == nil {
			if ss := filepath.Base(link); strings.Contains(ss, subsystem) {
				env["SUBSYSTEM"] = ss
			} else {
				return nil
			}

		}

		// get human readable product name.
		product := filepath.Join(kernelObject, "product")
		if _, err := os.Stat(product); err == nil {
			b, err := ioutil.ReadFile(product)
			if err != nil {
				return err
			}
			env["PRODUCTNAME"] = string(b)
		}

		if len(env) < 1 {
			return nil
		}

		if env["DRIVER"] != "usb" {
			return nil
		}
		devices = append(devices,
			Device{
				obj: kernelObject,
				env: env,
			})

		return nil
	})

	sort.Slice(devices, func(i, j int) bool {
		return devices[i].obj > devices[j].obj
	})

	return devices, err
}

// getEventFromUEventFile return all env var define in file
// syntax: name=value for each line
// Function use for /sys/.../uevent files
func getEventFromUEventFile(path string) (rv map[string]string, err error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}

	defer f.Close()

	data, err := ioutil.ReadAll(f)
	if err != nil {
		return nil, err
	}

	rv = make(map[string]string)
	buf := bufio.NewScanner(bytes.NewBuffer(data))

	var line string
	for buf.Scan() {
		line = buf.Text()
		field := strings.SplitN(line, "=", 2)
		if len(field) != 2 {
			return
		}
		rv[field[0]] = field[1]
	}

	return
}