[project] Clean up src/ tree

A long overdue cleanup of the src/ tree.

- Moved src/drivers to src/user because it contains more than drivers
- Removed src/drivers/ahci because it's unused - will restore it when I
  make a real AHCI driver
- Removed unused src/tools
- Moved kernel.ld (the only used file under src/arch) to src/kernel for
  now, if/when there's a multi-platform effort that should be figured
  out as part of it
- Removed the rest of the unused src/arch
- Renamed 'fb' to 'drv.uefi_fb' and 'nulldrv' to 'testapp'

src/user/drv.uefi_fb/main.cpp

@@ -0,0 +1,139 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "j6/init.h"
+#include "j6/errors.h"
+#include "j6/flags.h"
+#include "j6/signals.h"
+#include "j6/syscalls.h"
+#include "j6/types.h"
+
+#include "font.h"
+#include "screen.h"
+#include "scrollback.h"
+
+extern "C" {
+	int main(int, const char **);
+	void _get_init(size_t *initc, struct j6_init_value **initv);
+}
+
+extern j6_handle_t __handle_sys;
+extern j6_handle_t __handle_self;
+
+struct entry
+{
+	uint8_t bytes;
+	uint8_t area;
+	uint8_t severity;
+	uint8_t sequence;
+	char message[0];
+};
+
+int
+main(int argc, const char **argv)
+{
+	j6_system_log("fb driver starting");
+
+	size_t initc = 0;
+	j6_init_value *initv = nullptr;
+	_get_init(&initc, &initv);
+
+	j6_init_framebuffer *fb = nullptr;
+	for (unsigned i = 0; i < initc; ++i) {
+		if (initv[i].type == j6_init_desc_framebuffer) {
+			fb = reinterpret_cast<j6_init_framebuffer*>(initv[i].data);
+			break;
+		}
+	}
+
+	if (!fb || fb->addr == 0) {
+		j6_system_log("fb driver didn't find a framebuffer, exiting");
+		return 1;
+	}
+
+	j6_handle_t fb_handle = j6_handle_invalid;
+	uint32_t flags =
+		j6_vm_flag_write |
+		j6_vm_flag_write_combine;
+	j6_status_t s = j6_system_map_mmio(__handle_sys, &fb_handle, fb->addr, fb->size, flags);
+	if (s != j6_status_ok) {
+		return s;
+	}
+
+	s = j6_vma_map(fb_handle, __handle_self, fb->addr);
+	if (s != j6_status_ok) {
+		return s;
+	}
+
+	const screen::pixel_order order = (fb->flags & 1) ?
+		screen::pixel_order::bgr8 : screen::pixel_order::rgb8;
+
+	screen scr(
+		reinterpret_cast<void*>(fb->addr),
+		fb->horizontal,
+		fb->vertical,
+		fb->scanline,
+		order);
+
+	font fnt;
+
+	screen::pixel_t fg = scr.color(0xb0, 0xb0, 0xb0);
+	screen::pixel_t bg = scr.color(49, 79, 128);
+	scr.fill(bg);
+	scr.update();
+
+	constexpr int margin = 2;
+	const unsigned xstride = (margin + fnt.width());
+	const unsigned ystride = (margin + fnt.height());
+	const unsigned rows = (scr.height() - margin) / ystride;
+	const unsigned cols = (scr.width() - margin) / xstride;
+
+	scrollback scroll(rows, cols);
+
+	int pending = 0;
+	constexpr int pending_threshold = 5;
+
+	j6_handle_t sys = __handle_sys;
+	size_t buffer_size = 0;
+	void *message_buffer = nullptr;
+
+	while (true) {
+		size_t size = buffer_size;
+		j6_status_t s = j6_system_get_log(sys, message_buffer, &size);
+
+		if (s == j6_err_insufficient) {
+			free(message_buffer);
+			message_buffer = malloc(size * 2);
+			buffer_size = size;
+			continue;
+		} else if (s != j6_status_ok) {
+			j6_system_log("fb driver got error from get_log, quitting");
+			return s;
+		}
+
+		if (size > 0) {
+			entry *e = reinterpret_cast<entry*>(message_buffer);
+
+			size_t eom = e->bytes - sizeof(entry);
+			e->message[eom] = 0;
+
+			scroll.add_line(e->message, eom);
+			if (++pending > pending_threshold) {
+				scroll.render(scr, fnt);
+				scr.update();
+				pending = 0;
+			}
+		} else {
+			if (pending) {
+				scroll.render(scr, fnt);
+				scr.update();
+				pending = 0;
+			}
+		}
+	}
+
+	j6_system_log("fb driver done, exiting");
+	return 0;
+}
+