print: Allow for more than one output for console messages

include/print.h

@@ -21,7 +21,9 @@
 #ifndef PRINT_H
 #define PRINT_H
 
-void print_init(int (*putc)(char));
+int print_register_func_early(int (*putc)(char));
+int print_register_func(int (*putc)(char));
+int print_unregister_func(int (*putc)(char));
 int print(char *fmt, ...);
 int print_func(int (putcf)(char), char *fmt, ...);
 

kernel/print.c

@@ -18,20 +18,72 @@
     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include <init.h>
+#include <list.h>
+#include <kmalloc.h>
 #include <print.h>
 #include <vargs.h>
 
-/* This function exists solely so crashes don't happen if putc() gets
- * called before it is initialized. */
-int putc_initial(char c) {
-	(void)c;
+struct dlist_node print_funcs_list;
+
+struct print_func {
+	int (*putc)(char);
+	struct dlist_node list;
+};
+
+/*
+ * On startup, we'd like to have print capabilities before kmalloc is
+ * initialized, so statically allocate one struct print_func to allow for the
+ * registration of one print 'sink' before kmalloc is initialized.
+ */
+struct print_func print_func_early;
+int print_register_func_early(int (*putc)(char)) {
+	if (list_empty(&print_funcs_list)) {
+		print_func_early.putc = putc;
+		insert_before(&print_funcs_list, &print_func_early.list);
 		return 0;
 	}
-int (*print_putc)(char) = &putc_initial;
+	return -1;
+}
 
-void print_init(int (*putcfn)(char)) {
-	if (putcfn)
-		print_putc = putcfn;
+int print_register_func(int (*putc)(char)) {
+	struct print_func *pf;
+	if (!(pf = kmalloc(sizeof(struct print_func))))
+		return -1;
+
+	pf->putc = putc;
+	insert_before(&print_funcs_list, &pf->list);
+	return 0;
+}
+
+int print_unregister_func(int (*putc)(char)) {
+	struct print_func *it;
+
+	if (list_empty(&print_funcs_list))
+		return -1;
+
+	for_each_list(it, &print_funcs_list, struct print_func, list) {
+		if (it->putc == putc) {
+			remove(&it->list);
+
+			//only kfree if it was kmalloced
+			if (it != &print_func_early)
+				kfree(it);
+			return 0;
+		}
+	}
+	return -1;
+}
+
+int print_putc(char c) {
+	struct print_func *it;
+
+	if (list_empty(&print_funcs_list))
+		return -1;
+
+	for_each_list(it, &print_funcs_list, struct print_func, list)
+		it->putc(c);
+	return 0;
 }
 
 void puts(int (*putc)(char), const char *s)
@@ -132,7 +184,7 @@ int print(char *fmt, ...) {
 	va_list arg;
 
 	va_start(arg, fmt);
-	ret = _print(print_putc, fmt, arg);
+	ret = _print(&print_putc, fmt, arg);
 	va_end(arg);
 
 	return ret;
@@ -149,3 +201,9 @@ int print_func(int (*putc)(char), char *fmt, ...) {
 
 	return ret;
 }
+
+void print_init() {
+	init_list(&print_funcs_list);
+}
+
+early_initcall(print_init);

kernel/start_kernel.c

@@ -59,6 +59,7 @@ void video_console_init(void) {
 	if ((console_init(&console_fb)))
 		return;
 
+	print_register_func(&console_putc);
 	print_console_logo();
 
 	print_func(&console_putc, "Successfully initialized video console on %s.\n", fbdev->name);
@@ -70,7 +71,7 @@ void serial_console_init() {
 	if (!sdev)
 		return;
 
-	print_init(sdev->putc);
+	print_register_func_early(sdev->putc);
 	print("Successfully initialized serial console on %s\n", sdev->name);
 }