write some starting code to get basic option functionality

src/main.c

@@ -0,0 +1,77 @@
+#include <getopt.h>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdnoreturn.h>
+#include <sys/sysinfo.h>
+#include <unistd.h>
+
+enum opt {
+	OPT_LIST_CORES = 1, // option that lists the total amount of cores that are set
+	OPT_SET_ALL = 2,    // option to set all cores, regardless of their assumed state
+	OPT_VERBOSE = 4,    // print which cores are disabled/enabled
+	OPT_INVERT = 8,     // 'num' now represents the amount of cores to disable
+};
+
+noreturn void fatal(char const* fmt, ...) {
+	char buf[128];
+	va_list args;
+	va_start(args, fmt);
+	vsnprintf(buf, 128, fmt, args);
+	va_end(args);
+
+	fprintf(stderr, "\033[91mE: %s\033[0m\n", buf);
+	exit(1);
+}
+
+uint8_t getoptions(int32_t argc, char* const* argv, int32_t* ncpus) {
+	uint8_t opts = 0;
+	char opt;
+
+	char const* const msg = "-%c has already been set";
+	while ((opt = getopt(argc, argv, "lavi")) != -1) {
+		switch (opt) {
+		case 'l':
+			if (opts & OPT_LIST_CORES) fatal(msg, 'l');
+			opts |= OPT_LIST_CORES;
+			break;
+		case 'a':
+			if (opts & OPT_SET_ALL) fatal(msg, 'a');
+			opts |= OPT_SET_ALL;
+			break;
+		case 'v':
+			if (opts & OPT_VERBOSE) fatal(msg, 'v');
+			opts |= OPT_VERBOSE;
+			break;
+		case 'i':
+			if (opts & OPT_INVERT) fatal(msg, 'i');
+			opts |= OPT_INVERT;
+			break;
+		case '?':
+			fatal("usage: %s [number] [-l] [-a] [-v] [-i]", argv[0]);
+		}
+	}
+
+	if (optind < argc) {
+		char* num = argv[optind];
+		*ncpus = atoi(num);
+	} else fatal("you must provide a number!");
+
+	return opts;
+}
+
+int32_t main(int32_t argc, char** argv) {
+	if (geteuid() != 0) fatal("must be executed as the root user!");
+
+	int32_t ncpus;                                 // the number of CPUs to activate
+	uint8_t opts = getoptions(argc, argv, &ncpus); // the options to use
+	int32_t mcpus = get_nprocs_conf();             // the max number of CPUs that are available
+
+	if (opts & OPT_INVERT)
+		ncpus = mcpus - ncpus;
+
+	if (ncpus > mcpus) fatal("%i exeeds the maximum numbers of cpus available (%i)", ncpus, mcpus);
+	if (ncpus < 1) fatal("may not keep less than 1 cpu enabled, requested to enable %i", ncpus);
+	return 0;
+}