kernel: add e9 device for debugging

kernel-src/arch/x86-64/e9.c

@@ -1,4 +1,6 @@
 #include <arch/io.h>
+#include <kernel/devfs.h>
+#include <logging.h>
 
 void arch_e9_putc(char c) {
 #ifdef X86_64_ENABLE_E9
@@ -13,3 +15,23 @@ void arch_e9_puts(char *c) {
 	}
 #endif
 }
+
+static int devwrite(int minor, void *bufferp, size_t count, uintmax_t offset, int flags, size_t *wcount) {
+	uint8_t *buffer = bufferp;
+
+	for (uintmax_t i = 0; i < count; ++i)
+		outb(0xe9, buffer[i]);
+
+	*wcount = count;
+	return 0;
+}
+
+static devops_t devops = {
+	.write = devwrite
+};
+
+void arch_e9_initdev() {
+#ifdef X86_64_ENABLE_E9
+	__assert(devfs_register(&devops, "e9", V_TYPE_CHDEV, DEV_MAJOR_E9, 0, 0644) == 0);
+#endif
+}

kernel-src/arch/x86-64/main.c

@@ -63,6 +63,7 @@ void kernel_entry() {
 
 	block_init();
 	pseudodevices_init();
+	arch_e9_initdev();
 	pci_init();
 	keyboard_init();
 	arch_ps2_init();

kernel-src/include/kernel/devfs.h

@@ -12,6 +12,7 @@
 #define DEV_MAJOR_FB 5
 #define DEV_MAJOR_KEYBOARD 6
 #define DEV_MAJOR_BLOCK 7
+#define DEV_MAJOR_E9 8
 
 typedef struct {
 	int (*open)(int minor, int flags);

kernel-src/include/x86-64/arch/e9.h

@@ -3,5 +3,6 @@
 
 void arch_e9_putc(char);
 void arch_e9_puts(char *);
+void arch_e9_initdev();
 
 #endif