From d0247218a8d1130b29028bc6413f51eb01c71740 Mon Sep 17 00:00:00 2001
From: Stefan Huber <shuber@sthu.org>
Date: Mon, 2 Dec 2024 20:24:27 +0100
Subject: [PATCH] linux: Support power_now in sysfs for
 get_battery_power_draw()

Not all systems report current_now through the power supply sysfs
interface, but some do report power_now instead. Add support for these,
too.

The new implementation first tries power_now and then falls back to
computing power as the product of current and voltage. The new
implementation also reduces memory footprint on the stack by some 512k.
Also the old implementation potentially left files open under some
circumstances.
---
 src/linux.cc | 61 +++++++++++++++++++++++++++++++---------------------
 1 file changed, 37 insertions(+), 24 deletions(-)

diff --git a/src/linux.cc b/src/linux.cc
index 6ba8da44..4bf689a1 100644
--- a/src/linux.cc
+++ b/src/linux.cc
@@ -2360,35 +2360,48 @@ void get_battery_short_status(char *buffer, unsigned int n, const char *bat) {
 }
 
 void get_battery_power_draw(char *buffer, unsigned int n, const char *bat) {
-  static int reported = 0;
-  char current_now_path[256], voltage_now_path[256], current_now_val[256],
-      voltage_now_val[256];
-  char *ptr;
-  long current_now, voltage_now;
-  FILE *current_now_file;
-  FILE *voltage_now_file;
-  double result;
+  static int reported_power = 0;
+  static int reported_other = 0;
+  char path[256];
+  char value[256];
+  FILE *fp;
+  char *ret;
 
-  snprintf(current_now_path, 255, SYSFS_BATTERY_BASE_PATH "/%s/current_now",
-           bat);
-  snprintf(voltage_now_path, 255, SYSFS_BATTERY_BASE_PATH "/%s/voltage_now",
-           bat);
+  snprintf(path, 255, SYSFS_BATTERY_BASE_PATH "/%s/power_now", bat);
+  fp = open_file(path, &reported_power);
+  if (fp != nullptr) {
+    ret = fgets(value, 256, fp);
+    fclose(fp);
 
-  current_now_file = open_file(current_now_path, &reported);
-  voltage_now_file = open_file(voltage_now_path, &reported);
-
-  if (current_now_file != nullptr && voltage_now_file != nullptr) {
-    if (fgets(current_now_val, 256, current_now_file) &&
-        fgets(voltage_now_val, 256, voltage_now_file)) {
-      current_now = strtol(current_now_val, &ptr, 10);
-      voltage_now = strtol(voltage_now_val, &ptr, 10);
-
-      result = current_now * (voltage_now / 1e12);
+    if (ret != nullptr) {
+      double result = strtol(value, NULL, 10) * 1e-6;
       snprintf(buffer, n, "%.1f", result);
+      return;
     }
-    fclose(current_now_file);
-    fclose(voltage_now_file);
   }
+
+  snprintf(path, 255, SYSFS_BATTERY_BASE_PATH "/%s/current_now", bat);
+  fp = open_file(path, &reported_other);
+  if (fp == nullptr)
+    return;
+  ret = fgets(value, 256, fp);
+  fclose(fp);
+
+  if (ret == nullptr)
+    return;
+  double result = strtol(value, NULL, 10) * 1e-6;
+
+  snprintf(path, 255, SYSFS_BATTERY_BASE_PATH "/%s/voltage_now", bat);
+  fp = open_file(path, &reported_other);
+  if (fp == nullptr)
+    return;
+  ret = fgets(value, 256, fp);
+  fclose(fp);
+
+  if (fp == nullptr)
+    return;
+  result *= strtol(value, NULL, 10) * 1e-6;
+  snprintf(buffer, n, "%.1f", result);
 }
 
 int _get_battery_perct(const char *bat) {