WSLでEmacsのbattery.elを使えるようにする

背景

paypay20%キャンペーンと18,000円キャシュバックに惹かれて
Surface pro 6 を購入し、Emacs環境をWSLで新たに構築しました
その際に、タイトルバーに表示していたバッテリー残量が出ていませんでした
携帯機なのでバッテリー表示は必須と思い対策を調査しました

結論

下記コードで解決

battery-wsl.el

;; battery-modeの設定
(setq battery-status-function #'battery-linux-sysfs-wsl) ; バッテリー情報取得関数を独自のものに置き換える
;;(setq battery-update-interval 60) ; 必要があれば更新頻度設定[sec]
(display-battery-mode 1)
(setq battery-mode-line-format " %b%p%%")

;; タイトルバーに時計とバッテリー情報表示（こちらを使用するのであれば上記のbattery-modeの設定は不要）
(when (window-system)
  ;; display-timeより先にsetしておかないとdefaultの書式になる
  (setq display-time-string-forms
    '((format "%s/%s/%s" year month day)
      (format "(%s:%s)" 24-hours minutes)))
  ;;(setq display-time-interval 1)
  (display-time) ;; display-time-stringの有効化
  ;; タイトルバーの書式設定 global-mode-stringにdisplay-time-stringが入っている
  ;; バッファがファイルのときはフルパス、でなければバッファ名表示
  ;; if(buffer-file-name) の評価がsetq時で終わらないよう:eval
  (setq battery-status-function #'battery-linux-sysfs-wsl)
  ;;(setq battery-update-interval 1)
  (display-battery-mode 1)
  (setq battery-mode-line-format " %b%p%%")
  (setq frame-title-format '("" (:eval (if (buffer-file-name) " %f" " %b"))
                 " --- " global-mode-string) ) )

;; バッテリー取得関数本体（でかいのでinit-loaderで分割をオススメ）
(defun battery-linux-sysfs-wsl ()
  "Get ACPI status information from Linux kernel.
This function works only with the Windows Subsystem for Linux.

The following %-sequences are provided:
%c Current capacity (mAh)
%r Current rate
%B Battery status (verbose)
%b Battery status (charging:'+' discharging:'')
%d Temperature (in degrees Celsius)
%p Battery load percentage
%L AC line status (verbose)
%m Remaining time (to charge or discharge) in minutes
%h Remaining time (to charge or discharge) in hours
%t Remaining time (to charge or discharge) in the form `h:min'"
  (let (charging-state ac-state temperature hours
               energy-now energy-now-rate power-now current-now voltage-now
               (dir "/sys/class/power_supply/battery"))
    (with-temp-buffer
      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "capacity" dir)))
      (setq energy-now-rate (or (thing-at-point 'number) "N/A"))

      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "status" dir)))
      (setq charging-state (or (thing-at-point 'word) "N/A"))

      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "temp" dir)))
      (setq temperature (or (thing-at-point 'number) "N/A"))
      (setq temperature (if (numberp temperature) (* temperature 0.1)))

      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "charge_counter" dir)))
      (setq energy-now (or (thing-at-point 'number) "N/A"))

      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "current_now" dir)))
      (setq current-now (or (thing-at-point 'number) "N/A"))
      (unless (or   (stringp energy-now) (stringp current-now)
            (stringp energy-now-rate) (zerop current-now))
    (if (string= charging-state "Discharging")
        (setq hours (/ energy-now current-now))
      (setq hours (/ (* energy-now (- 100.0 energy-now-rate))
             energy-now-rate current-now ))))

      (erase-buffer)
      (ignore-errors (insert-file-contents
              (expand-file-name "voltage_now" dir)))
      (setq voltage-now (or (thing-at-point 'number) "N/A"))
      (setq power-now (if (and (numberp current-now) (numberp voltage-now))
              (* (/ current-now 1000.0) (/ voltage-now 1000000.0))))
      ;; current-now[mA]->[A] voltage-now[uV]->[V]

      (erase-buffer)
      (setq dir "/sys/class/power_supply/ac")
      (ignore-errors (insert-file-contents
              (expand-file-name "online" dir)))
      (setq ac-state (cond ((eq (thing-at-point 'number) 1) "AC")
               ((eq (thing-at-point 'number) 0) "BAT")
               (t "N/A")))
      )
    ;; set return value
    (list (cons ?c (number-to-string energy-now))
      (cons ?r (if hours (number-to-string power-now) "N/A"))
      (cons ?B charging-state)
      (cons ?b (if (string= charging-state "Charging") "+" ""))
      (cons ?d (number-to-string temperature))
      (cons ?p (number-to-string energy-now-rate))
      (cons ?L ac-state)
      (cons ?m (if hours (format "%d" (* hours 60)) "N/A"))
      (cons ?h (if hours (format "%d" hours) "N/A"))
      (cons ?t (if hours (format "%d:%02d" hours (* (- hours (floor hours)) 60)) "N/A")))
    )
)

一応、関数本体だけの.elをこちら#githubに用意しました

調査ログ

バッテリー情報取得関数を探す

モードラインへの表示を制御するのに以下ように設定していました
(setq battery-mode-line-format " %b%p%%")
このbattery-mode-line-formatをC-h vで変数の*Help*を見てみると

*Help*

battery-mode-line-format is a variable defined in ‘battery.el’.
Its value is " %b%p%%"
Original value was nil

Documentation:
Control string formatting the string to display in the mode line.
Ordinary characters in the control string are printed as-is, while
conversion specifications introduced by a ‘%’ character in the control
string are substituted as defined by the current value of the variable
‘battery-status-function’.  Here are the ones generally available:
%c Current capacity (mAh or mWh)
%r Current rate of charge or discharge
%B Battery status (verbose)
%b Battery status: empty means high, ‘-’ means low,
   ‘!’ means critical, and ‘+’ means charging
%d Temperature (in degrees Celsius)
%L AC line status (verbose)
%p Battery load percentage
%m Remaining time (to charge or discharge) in minutes
%h Remaining time (to charge or discharge) in hours
%t Remaining time (to charge or discharge) in the form ‘h:min’

You can customize this variable.

battery-status-function変数の値によって%*が差し替えられるとあります

というわけで、battery-status-function変数に入っている関数が
バッテリー情報を取得していると推測されます

現在の値は*Help*内のbattery-status-functionのリンクをRETすると

battery-status-function is a variable defined in ‘battery.el’.
Its value is nil

  This variable may be risky if used as a file-local variable.

Documentation:
Function for getting battery status information.
The function has to return an alist of conversion definitions.
Its cons cells are of the form

    (CONVERSION . REPLACEMENT-TEXT)

CONVERSION is the character code of a "conversion specification"
introduced by a ‘%’ character in a control string.

You can customize this variable.

nilとなっております
*Help*内のbattery.elのリンクからコードへジャンプすると

battery.el

(defcustom battery-status-function
  (cond ((and (eq system-type 'gnu/linux)
          (file-readable-p "/proc/apm"))
     #'battery-linux-proc-apm)
    ((and (eq system-type 'gnu/linux)
          (file-directory-p "/proc/acpi/battery"))
     #'battery-linux-proc-acpi)
    ((and (eq system-type 'gnu/linux)
          (file-directory-p "/sys/class/power_supply/")
          (directory-files "/sys/class/power_supply/" nil
                               battery--linux-sysfs-regexp))
     #'battery-linux-sysfs)
    ((and (eq system-type 'berkeley-unix)
          (file-executable-p "/usr/sbin/apm"))
     #'battery-bsd-apm)
    ((and (eq system-type 'darwin)
          (condition-case nil
          (with-temp-buffer
            (and (eq (call-process "pmset" nil t nil "-g" "ps") 0)
             (> (buffer-size) 0)))
        (error nil)))
     #'battery-pmset)
    ((fboundp 'w32-battery-status)
     #'w32-battery-status))
  "Function for getting battery status information.
The function has to return an alist of conversion definitions.
Its cons cells are of the form

    (CONVERSION . REPLACEMENT-TEXT)

CONVERSION is the character code of a \"conversion specification\"
introduced by a `%' character in a control string."
  :type '(choice (const nil) function)
  :group 'battery)

とあり、環境によって

• battery-linux-proc-apm
• battery-linux-proc-acpi
• battery-linux-sysfs
• battery-bsd-apm
• battery-pmset
• w32-battery-status

がセットされるようです

このなかでWSL環境に近いのは、Pathが"/sys/class/power_supply/"でセットされる
battery-linux-sysfsなのでこの関数が目的の関数となります

バッテリー情報が取れない原因

WSLでは一般のlinux環境とは異なるpathでバッテリー情報を提供しているためでした
battery-linux-sysfsでは"/sys/class/power_supply/bat0/"を期待しているのですが
WSL環境では、"/sys/class/power_supply/battery/"となっており、その配下のファイル構成も異なっております

shell.log

$ ls /sys/class/power_supply/
ac  battery  usb
$ ls /sys/class/power_supply/battery/
capacity  charge_counter  current_now  health  present  status  technology  temp  type  voltage_now
$ cat /sys/class/power_supply/battery/capacity
64 # 残量[%]
$ cat /sys/class/power_supply/battery/charge_counter 
3959 # 充電容量[mAh]
$ cat /sys/class/power_supply/battery/current_now 
705 # 電流[mA]
$ cat /sys/class/power_supply/battery/health 
Good # 劣化状態
$ cat /sys/class/power_supply/battery/present 
1 # 電力供給状態?
$ cat /sys/class/power_supply/battery/status 
Discharging # 充電状態(非充電中)
$ cat /sys/class/power_supply/battery/status 
Charging # 充電状態(充電中)
$ cat /sys/class/power_supply/battery/status 
Full # 充電状態(充電完了)
$ cat /sys/class/power_supply/battery/technology 
Li-ion # 製品仕様
$ cat /sys/class/power_supply/battery/temp
258 # 温度 摂氏x10 ?
$ cat /sys/class/power_supply/battery/type
Battery # 電力供給仕様
$ cat /sys/class/power_supply/battery/voltage_now 
8115000 # 電圧 [uV]　=> 8.115[V] ?

WSL用のバッテリー情報取得関数の設計

バッテリー情報取得関数が返す必要がある情報は
battery-linux-sysfsを参考にすると

*Help*

battery-linux-sysfs is a compiled Lisp function in ‘battery.el’.

(battery-linux-sysfs)

Get ACPI status information from Linux kernel.
This function works only with the new ‘/sys/class/power_supply/’
format introduced in Linux version 2.4.25.

The following %-sequences are provided:
%c Current capacity (mAh or mWh)
%r Current rate
%B Battery status (verbose)
%d Temperature (in degrees Celsius)
%p Battery load percentage
%L AC line status (verbose)
%m Remaining time (to charge or discharge) in minutes
%h Remaining time (to charge or discharge) in hours
%t Remaining time (to charge or discharge) in the form ‘h:min’

%c Current capacity (mAh or mWh)

charge_counterの値を返したら良さそう

%r Current rate

current_nowとvoltate_nowの積で電力[w]を計算したらいけそう

%B Battery status (verbose)

battery/statusの値を返したら良さそう

%d Temperature (in degrees Celsius)

tempの値を返したら良さそう

%p Battery load percentage

capacityの値を返したら良さそう

%L AC line status (verbose)

ac/statusの値を返したら良さそう

%m Remaining time (to charge or discharge) in minutes

%h Remaining time (to charge or discharge) in hours

%t Remaining time (to charge or discharge) in the form `h:min'"

2つのアルゴリズムが必要

残り稼働時間(非充電時)

残り稼働時間[h] = 電池残容量[Wh] / 消費電力[Wh] = 電池容量[Ah] / 消費電力[Ah]
電池容量[Ah] = charge_counter[mAh] * 1000
消費電力[Ah] = current_now[mA] * 1000 * 1[h]

残り充電時間(充電時)

残り充電時間[h] = (電池満容量[Wh] - 電池残容量[Wh]) / 供給電力[Wh]
電池満容量[Wh]が情報としてないので
電池満容量[Wh] * 電池残量[%] = 電池残容量[Wh]
電池満容量[Wh] = 電池残容量[Wh] / 電池残量[%]

(電池満容量[Wh] - 電池残容量[Wh]) = 電池残容量[Wh] / 電池残量[%] - 電池残量[%]
= 電池残容量[Wh] * (1 - 電池残量[%]) / 電池残量[%]
= V[V] * charge_counter[mAh] * 1000 * (1 - capacity) / capacity
残り充電時間[h] = V[V] * charge_counter[mAh] * 1000 * (1 - capacity) / capacity / (V[V] * current_now[mA] * 1000 * 1[h])
= charge_counter[mAh] * (1 - capacity) / capacity / current_now[mA]

WSL用のバッテリー情報取得関数の実装

前章で述べた情報を
(list (cons ?c val) (cons ?r val) ...)
の形で返す関数を実装します
lispなので最後に評価されたS式が戻り値となります

battery-wsl.el

(let (charging-state ac-state temperature hours
             energy-now energy-now-rate power-now current-now voltage-now
             (dir "/sys/class/power_supply/battery"))
  (with-temp-buffer ;; このブロック限りのバッファを生成しcurrent_bufferとする
    (erase-buffer) ;; バッファに読み込む前にバッファを空に
        (ignore-errors (insert-file-contents
            (expand-file-name "capacity" dir)))
    (setq energy-now-rate (or (thing-at-point 'number) "N/A"))

    (erase-buffer)
    (ignore-errors (insert-file-contents
            (expand-file-name "status" dir)))
    (setq charging-state (or (thing-at-point 'word) "N/A"))

    (erase-buffer)
    (ignore-errors (insert-file-contents
            (expand-file-name "temp" dir)))
    (setq temperature (or (thing-at-point 'number) "N/A"))
    (setq temperature (if (numberp temperature) (* temperature 0.1)))

    (erase-buffer)
    (ignore-errors (insert-file-contents
            (expand-file-name "charge_counter" dir)))
    (setq energy-now (or (thing-at-point 'number) "N/A"))

    (erase-buffer)
    (ignore-errors (insert-file-contents
            (expand-file-name "current_now" dir)))
    (setq current-now (or (thing-at-point 'number) "N/A"))
    (unless (or (stringp energy-now) (stringp current-now)
        (stringp energy-now-rate) (zerop current-now))
      ;; 変数がN/Aのときパス。充電完了となるとcurrent-now=0。zero-dev回避のため0のときパス
      (if (string= charging-state "Discharging")
          (setq hours (/ energy-now current-now))
        (setq hours (/ (* energy-now (- 100.0 energy-now-rate))
                   energy-now-rate current-now ))))

    (erase-buffer)
    (ignore-errors (insert-file-contents
            (expand-file-name "voltage_now" dir)))
    (setq voltage-now (or (thing-at-point 'number) "N/A"))
    (setq power-now (if (and (numberp current-now) (numberp voltage-now))
            (* (/ current-now 1000.0) (/ voltage-now 1000000.0))))
    ;; current-now[mA]->[A] voltage-now[uV]->[V]

    (erase-buffer)
    (setq dir "/sys/class/power_supply/ac") ;; acはpathが変わるので変更
    (ignore-errors (insert-file-contents
            (expand-file-name "online" dir)))
    (setq ac-state (cond ((eq (thing-at-point 'number) 1) "AC")
             ((eq (thing-at-point 'number) 0) "BAT")
             (t "N/A")))
    )
  ;; 戻り値(リスト型)を設定
  (list (cons ?c energy-now)
    (cons ?r (if hours power-now "N/A"))
    (cons ?B charging-state)
    (cons ?d temperature)
    (cons ?p energy-now-rate)
    (cons ?L ac-state)
    (cons ?m (if hours (format "%d" (* hours 60)) "N/A"))
    (cons ?h (if hours (format "%d" hours) "N/A"))
    (cons ?t (if hours (format "%d:%02d" hours (* (- hours (floor hours)) 60)) "N/A")))
  )

こいつをdefunで囲えば完成です

最後に

今回は、実装までの過程を詳細に書いてみました
Emacsにはeldocや*Help*が用意されている上に
ソースコードにも直接アクセスできるのですが
その活かし方がイマイチ広まってないと思います
*Help*が使いこなせるとEmacsの拡張がもっと楽しめるので
皆さん使って見ましょう

• C-h v 変数(variable)のhelp
• C-h f 関数(function)のhelp
• C-h b キーマップ(bind)のhelp