add makefile, fix annoying errors

include/utils.h

@@ -1,8 +1,7 @@
 #ifndef LINUXSMARTIE_UTILS_H
 #define LINUXSMARTIE_UTILS_H
 
-#include <stddef.h>
-#include <time.h>
+#include <sys/types.h>
 
 #if __STDC_VERSION__ >= 202000L
 #define C_STD "C23"
@@ -22,11 +21,11 @@
 #define P_BYTES(bytes, start) pretty_bytes((bytes), (start), (char[16]){0}, 16)
 #define P_NUM(num) pretty_num((num), (char[16]){0}, 16)
 
-int get_instance_lock(void);
+int get_instance_lock();
 
 void timespec_add_ms(struct timespec *ts, uint16_t ms);
 
-uint64_t timespec_diff_us(const struct timespec *a, const struct timespec *b);
+int64_t timespec_diff_us(const struct timespec *a, const struct timespec *b);
 
 char *pretty_num(double num, char *buf, size_t bufsz);
 
@@ -34,7 +33,7 @@ char *pretty_bytes(uint64_t bytes, int8_t start_suffix, char *buf, size_t bufsz)
 
 int get_hwmon_dir(char *path, size_t bufsz);
 
-size_t read_file(const char *dir, const char *file, char *buffer, size_t n);
+ssize_t read_file(const char *dir, const char *file, char *buffer, size_t n);
 
 void fast_read_num_u64(const char *dir, const char *file, char *buf, uint64_t *result, uint32_t divider);