add cpu handling functions

add the functions which handle the /sys/devices/cpu/cpuX/online files

src/main.c

@@ -1,5 +1,6 @@
 #include <getopt.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -14,6 +15,8 @@ enum opt {
 	OPT_INVERT = 8,     // 'num' now represents the amount of cores to disable
 };
 
+char const* const cpu_path = "/sys/devices/system/cpu/cpu%i/online";
+
 noreturn void fatal(char const* fmt, ...) {
 	char buf[128];
 	va_list args;
@@ -61,6 +64,37 @@ uint8_t getoptions(int32_t argc, char* const* argv, int32_t* ncpus) {
 	return opts;
 }
 
+bool getcore(uint32_t id) {
+	// get the file path
+	char path[64];                    // contains the file path (max length is 64 due to the path and a bunch of extra wiggle room)
+	snprintf(path, 64, cpu_path, id); // writes the path using the id
+
+	// if the file doesn't exist; return true
+	if (access(path, R_OK) != 0)
+		return true;
+
+	// read a character from the file, store in state
+	char state = '\0';
+	FILE* f = fopen(path, "r");
+	fread(&state, 1, 1, f);
+	fclose(f);
+
+	// return whether state is truthy
+	return !!state;
+}
+
+void setcore(uint32_t id, bool state) {
+	char path[64];
+	snprintf(path, 64, cpu_path, id);
+
+	char s = 0x30 + (char)state; // convert the state to a character
+
+	// write the state to the file (creates file if it doesn't exist)
+	FILE* f = fopen(path, "w");
+	fwrite(&s, 1, 1, f);
+	fclose(f);
+}
+
 int32_t main(int32_t argc, char** argv) {
 	if (geteuid() != 0) fatal("must be executed as the root user!");