Organize system calls

* syscalls should all return j6_status_t now
* syscalls are grouped by category in name as well as in files

src/drivers/nulldrv/main.cpp

@@ -1,12 +1,15 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include "j6/types.h"
+#include "j6/errors.h"
+
 extern "C" {
-	int32_t getpid();
-	int32_t fork();
-	void sleep(uint64_t til);
-	void debug();
-	void message(const char *msg);
+	j6_status_t getpid(uint64_t *);
+	j6_status_t fork(uint64_t *);
+	j6_status_t sleep(uint64_t til);
+	j6_status_t debug();
+	j6_status_t message(const char *msg);
 
 	int main(int, const char **);
 }
@@ -15,10 +18,21 @@ extern "C" {
 int
 main(int argc, const char **argv)
 {
-	int32_t pid = getpid();
-	int32_t child = fork();
+	uint64_t pid = 0;
+	uint64_t child = 0;
+
+	j6_status_t result = fork(&child);
+	if (result != j6_status_ok)
+		return result;
+
 	message("hello from nulldrv!");
+
+	result = getpid(&pid);
+	if (result != j6_status_ok)
+		return result;
+
 	for (int i = 1; i < 5; ++i)
 		sleep(i*10);
-	return 0;
+
+	return pid;
 }