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.

include/input.h

@@ -0,0 +1,93 @@
+#pragma once
+
+#include "types.h"
+
+// Raw input events -- Linux's evdev interface.
+//
+// The console gives characters. That is the right thing for a shell and the
+// wrong thing for everything else: a character stream has no key *releases*,
+// no way to tell left shift from right, no notion of a key being held, and no
+// mouse at all. A game holding W to walk forward, or a compositor deciding
+// which window a click landed in, needs the events underneath the characters.
+//
+// The layout is Linux's, deliberately. It is what every program that reads input
+// already speaks -- SDL, X, libinput, every game engine -- so a program that
+// runs on Linux reads input here without a porting layer. It costs nothing to
+// match: the struct is four fields.
+//
+// Nodes are /dev/input/event0 (keyboard) and /dev/input/event1 (mouse).
+
+struct input_timeval {
+  int64 tv_sec;
+  int64 tv_usec;
+};
+
+struct input_event {
+  struct input_timeval time;
+  uint16 type;
+  uint16 code;
+  int32  value;
+};
+
+// Event types.
+#define EV_SYN          0x00
+#define EV_KEY          0x01
+#define EV_REL          0x02
+#define EV_ABS          0x03
+#define EV_MSC          0x04
+
+#define SYN_REPORT      0
+
+// Relative axes.
+#define REL_X           0x00
+#define REL_Y           0x01
+#define REL_WHEEL       0x08
+
+// Buttons live in the EV_KEY code space alongside keys, which is why the
+// keyboard's codes stop well below 0x100.
+#define BTN_LEFT        0x110
+#define BTN_RIGHT       0x111
+#define BTN_MIDDLE      0x112
+
+// Key codes worth naming. The rest are the AT scancode-set-1 numbers, which
+// Linux's keycodes were derived from and still match for everything below
+// 0x54 -- that is not a coincidence and it is why the PS/2 path needs no
+// translation table for unprefixed bytes.
+#define KEY_RESERVED    0
+#define KEY_ESC         1
+#define KEY_ENTER       28
+#define KEY_LEFTCTRL    29
+#define KEY_LEFTSHIFT   42
+#define KEY_RIGHTSHIFT  54
+#define KEY_LEFTALT     56
+#define KEY_SPACE       57
+#define KEY_RIGHTCTRL   97
+#define KEY_RIGHTALT    100
+#define KEY_HOME        102
+#define KEY_UP          103
+#define KEY_PAGEUP      104
+#define KEY_LEFT        105
+#define KEY_RIGHT       106
+#define KEY_END         107
+#define KEY_DOWN        108
+#define KEY_PAGEDOWN    109
+#define KEY_INSERT      110
+#define KEY_DELETE      111
+#define KEY_LEFTMETA    125
+#define KEY_RIGHTMETA   126
+
+#define KEY_MAX         255
+
+// EVIOCGRAB -- take/release exclusive access to a device.
+//
+// Linux's _IOW('E', 0x90, int). Spelled as the resulting constant rather than
+// built from an _IOW macro because Schunix has no ioctl-encoding macros and
+// inventing a set just for this would be a bigger change than the feature.
+// A non-zero argument grabs, zero releases; the argument is passed by value.
+#define EVIOCGRAB       0x40044590
+
+// Which device an event came from. Both are minor numbers under the input
+// major, and both are the index into the driver's array.
+#define INPUT_KBD       0
+#define INPUT_MOUSE     1
+#define NINPUTDEV       2