Kernel: Serial: Add serial_printf function

This function can output with decorators (like printf from stdio)

kernel/kernel/kernel.c

@@ -7,12 +7,12 @@
 
 void kernel_main(void) {
 	terminal_initialize();
+	init_serial();
 	printf("Hello from OrionOS!\n");
 	printf("Testing serial\n");
-	init_serial();
-	serial_print("Test is success!\n");
-	serial_print("Newline test\n");
-	serial_print("No newline test ");
-	serial_print("No newline test");
+	serial_printf("Test is success!\n");
+	serial_printf("Newline test\n");
+	char * test_string = "test";
+	serial_printf("This is string from variable: %s", test_string);
 	printf("Test finished success!\n");
 }

kernel/kernel/serial.h

@@ -1,5 +1,8 @@
 #include <stdint.h>
 #include <string.h>
+#include <stdarg.h>
+#include <limits.h>
+#include <stdbool.h>
 
 #define PORT 0x3f8          // COM1
  
@@ -38,23 +41,91 @@ char read_serial() {
 int is_transmit_empty() {
    return inb(PORT + 5) & 0x20;
 }
- 
+
 void write_serial(char a) {
    while (is_transmit_empty() == 0);
    
    outb(PORT, a);
 }
 
-void serial_print(const char* str, ...) {
-  size_t len = strlen(str);
-  for (size_t i=0; i < len; i++) {
-    if (str[i] == '\n') {
-	write_serial('\r');
-	write_serial('\n');
-    } else {
-      write_serial(str[i]);
-    }
-  }
+static bool print(const char* data, size_t length) {
+	const unsigned char* bytes = (const unsigned char*) data;
+	for (size_t i = 0; i < length; i++) {
+	  if (bytes[i] == '\n') {
+	    write_serial('\r');
+	    write_serial('\n');
+	  } else {
+	    write_serial(bytes[i]);
+	  }
+	}
+	return true;
+}
+
+int serial_printf(const char* restrict format, ...) {
+	va_list parameters;
+	va_start(parameters, format);
+
+	int written = 0;
+
+	while (*format != '\0') {
+		size_t maxrem = INT_MAX - written;
+
+		if (format[0] != '%' || format[1] == '%') {
+			if (format[0] == '%')
+				format++;
+			size_t amount = 1;
+			while (format[amount] && format[amount] != '%')
+				amount++;
+			if (maxrem < amount) {
+				// TODO: Set errno to EOVERFLOW.
+				return -1;
+			}
+			if (!print(format, amount))
+				return -1;
+			format += amount;
+			written += amount;
+			continue;
+		}
+
+		const char* format_begun_at = format++;
+
+		if (*format == 'c') {
+			format++;
+			char c = (char) va_arg(parameters, int /* char promotes to int */);
+			if (!maxrem) {
+				// TODO: Set errno to EOVERFLOW.
+				return -1;
+			}
+			if (!print(&c, sizeof(c)))
+				return -1;
+			written++;
+		} else if (*format == 's') {
+			format++;
+			const char* str = va_arg(parameters, const char*);
+			size_t len = strlen(str);
+			if (maxrem < len) {
+				// TODO: Set errno to EOVERFLOW.
+				return -1;
+			}
+			if (!print(str, len))
+				return -1;
+			written += len;
+		} else {
+			format = format_begun_at;
+			size_t len = strlen(format);
+			if (maxrem < len) {
+				// TODO: Set errno to EOVERFLOW.
+				return -1;
+			}
+			if (!print(format, len))
+				return -1;
+			written += len;
+			format += len;
+		}
+	}
+
+	va_end(parameters);
+	return written;
 }
 
 inline void outb(uint16_t port, uint8_t val)