Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

kernel/drivers/registry.c

@@ -0,0 +1,114 @@
+// The driver registry.
+//
+// One table, one line per driver. This is the same shape as
+// kernel/sys/table.inc and kernel/dev/cdev.c's devsw: a single place that
+// lists what exists, so a driver cannot be half-registered.
+//
+// It is a plain array rather than the linker-section trick a bigger kernel
+// would use (a __attribute__((section(".drivers"))) entry per driver, walked
+// between __start_ and __stop_ symbols). That approach lets a driver register
+// itself by existing, which is genuinely nicer -- but it also means the list
+// of what is in your kernel is not written down anywhere you can read, and
+// a driver silently dropped by the linker looks exactly like one that was
+// never written. At this size, being able to read the list wins.
+//
+// To add a driver: write kernel/drivers/<name>.c exporting a struct
+// pci_driver, declare it here, and add it to the array and to the Makefile's
+// KERN_DRIVERS.
+
+#include "types.h"
+#include "defs.h"
+#include "param.h"
+#include "spinlock.h"
+#include "sleeplock.h"
+#include "fs.h"
+#include "file.h"
+#include "pci.h"
+
+#include "usb.h"
+#include "device.h"
+
+extern const struct pci_driver vga_pci_driver;
+extern const struct pci_driver xhci_driver;
+extern const struct pci_driver virtio_gpu_driver;
+extern const struct pci_driver e1000_driver;
+
+// Order matters here in one respect: virtio-gpu is offered the bus before the
+// VBE framebuffer driver, so that on a machine with both, the device with real
+// mode setting and an explicit flush wins the display class. vga_pci still
+// claims the stdvga card underneath, which is what the boot splash and the
+// text console are drawn on.
+static const struct pci_driver *drivers[] = {
+    &virtio_gpu_driver,
+    &vga_pci_driver,
+    &e1000_driver,
+    &xhci_driver,
+};
+
+void
+pci_bind_all(void)
+{
+  for (unsigned i = 0; i < sizeof(drivers) / sizeof(drivers[0]); i++)
+    pci_bind(drivers[i]);
+}
+
+// USB class drivers, same arrangement and for the same reason. These are not
+// found on the PCI bus -- they are offered a device by the USB core once its
+// interface descriptor has been read -- but a driver you cannot find in a
+// list is a driver nobody knows is there, whichever bus it sits on.
+//
+// To add one: write kernel/drivers/usb_<name>.c exporting a struct
+// usb_driver, declare it here, add it to the array and to KERN_DRIVERS.
+
+extern const struct usb_driver usb_hid_driver;
+extern const struct usb_driver usb_storage_driver;
+extern const struct usb_driver usb_hub_driver;
+
+static const struct usb_driver *usb_drivers[] = {
+    &usb_hid_driver,
+    &usb_storage_driver,
+    &usb_hub_driver,
+};
+
+int usb_offer(const struct usb_driver *, struct usb_dev *);
+
+void
+usb_bind_all(struct usb_dev *dev)
+{
+  for (unsigned i = 0; i < sizeof(usb_drivers) / sizeof(usb_drivers[0]); i++)
+    if (usb_offer(usb_drivers[i], dev)) {
+      // Same as the PCI path: publish it in the bus-agnostic list so that
+      // "what is attached" has one answer covering every bus. Class comes from
+      // the driver that claimed it rather than the USB class code, because a
+      // driver knows what it made of the device and the descriptor only says
+      // what the device claims to be.
+      const char *n = usb_drivers[i]->name;
+      struct device *d = device_add(n, DEVBUS_USB, usb_drivers[i]->devclass, n);
+      if (d)
+        device_set_desc(d, usb_drivers[i]->name);
+      return;
+    }
+}
+
+// Devices that are not enumerated by any bus -- they are simply known to be
+// there on a PC, and the driver pokes fixed I/O ports to find out whether it
+// is right. Listing them matters because a device manager that shows the
+// graphics card but not the keyboard is not showing the machine.
+//
+// Registered here rather than inside each driver's init so that the whole set
+// is visible in one place, which is the same reasoning as the driver arrays
+// above.
+void
+platform_register_devices(void)
+{
+  struct device *d;
+
+  if ((d = device_add("kbd", DEVBUS_PLATFORM, DEVCLASS_INPUT, "ps2kbd")))
+    device_set_desc(d, "PS/2 keyboard");
+  if ((d = device_add("mouse", DEVBUS_PLATFORM, DEVCLASS_INPUT, "ps2mouse")))
+    device_set_desc(d, "PS/2 mouse");
+  if ((d = device_add("uart", DEVBUS_PLATFORM, DEVCLASS_OTHER, "uart8250")))
+    device_set_desc(d, "16550 serial port");
+  if ((d = device_add("ide", DEVBUS_PLATFORM, DEVCLASS_STORAGE, "ide")))
+    device_set_desc(d, "ATA disk controller");
+}