commit fc4b14bc2856fc43c1b6393acbfd045f7f3dd5fa
Author: Mika <kontakt@donau2space.de>
Date:   Thu Dec 4 15:57:39 2025 +0000

    Add main.c

diff --git a/main.c b/main.c
new file mode 100644
index 0000000..7f31a09
--- /dev/null
+++ b/main.c
@@ -0,0 +1,124 @@
+/*
+ * cpu_governor_monitor - Simple CLI tool to sample the current CPU governor
+ * and log it together with a caller-supplied C-state indicator.
+ */
+
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define GOVERNOR_PATH "/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor"
+
+struct cpu_log_entry {
+    char governor[30];
+    int c_state;
+    time_t timestamp;
+};
+
+static void trim_newline(char *str)
+{
+    if (!str) {
+        return;
+    }
+    size_t len = strcspn(str, "\r\n");
+    str[len] = '\0';
+}
+
+const char *get_current_governor(void)
+{
+    static char governor_buf[30] = "unknown";
+    FILE *file = fopen(GOVERNOR_PATH, "r");
+
+    if (!file) {
+        perror("fopen scaling_governor");
+        return governor_buf;
+    }
+
+    if (!fgets(governor_buf, sizeof(governor_buf), file)) {
+        perror("fgets scaling_governor");
+        snprintf(governor_buf, sizeof(governor_buf), "unknown");
+        fclose(file);
+        return governor_buf;
+    }
+
+    fclose(file);
+    trim_newline(governor_buf);
+    return governor_buf;
+}
+
+void log_cpu_state(const char *governor, int c_state)
+{
+    struct cpu_log_entry entry;
+    memset(&entry, 0, sizeof(entry));
+
+    if (governor) {
+        strncpy(entry.governor, governor, sizeof(entry.governor) - 1);
+    } else {
+        strncpy(entry.governor, "unknown", sizeof(entry.governor) - 1);
+    }
+
+    entry.c_state = c_state;
+    entry.timestamp = time(NULL);
+
+    char ts_buf[32];
+    struct tm tm_info;
+
+    if (localtime_r(&entry.timestamp, &tm_info) != NULL) {
+        strftime(ts_buf, sizeof(ts_buf), "%Y-%m-%d %H:%M:%S", &tm_info);
+    } else {
+        snprintf(ts_buf, sizeof(ts_buf), "unknown_time");
+    }
+
+    printf("timestamp=%s (epoch=%ld) governor=%s c_state=%d\n",
+           ts_buf,
+           (long)entry.timestamp,
+           entry.governor,
+           entry.c_state);
+}
+
+static void print_usage(const char *prog)
+{
+    fprintf(stderr, "Usage: %s [c_state]\n", prog);
+    fprintf(stderr, "If c_state is omitted, -1 is logged to indicate unknown.\n");
+}
+
+static int parse_c_state(const char *arg, int *c_state)
+{
+    char *endptr = NULL;
+    long value = strtol(arg, &endptr, 10);
+
+    if (endptr == arg || *endptr != '\0') {
+        return -1;
+    }
+
+    if (value < INT_MIN || value > INT_MAX) {
+        return -1;
+    }
+
+    *c_state = (int)value;
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    int c_state = -1;
+
+    if (argc > 2) {
+        print_usage(argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    if (argc == 2) {
+        if (parse_c_state(argv[1], &c_state) != 0) {
+            fprintf(stderr, "Invalid c_state value: %s\n", argv[1]);
+            return EXIT_FAILURE;
+        }
+    }
+
+    const char *governor = get_current_governor();
+    log_cpu_state(governor, c_state);
+    return EXIT_SUCCESS;
+}