include: one folder per subsystem, and includes that name it

Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".

Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

include/dev/kbd.h

@@ -0,0 +1,115 @@
+// PC keyboard interface constants
+//
+// The scancode tables themselves are no longer here. They moved to
+// kernel/dev/keymap.c when there became more than one of them -- a header
+// full of `static` arrays gives every file that includes it its own private
+// copy, which was harmless while exactly one file did.
+
+#ifndef KBD_H
+#define KBD_H
+
+#define KBSTATP         0x64    // kbd controller status port(I)
+#define KBS_DIB         0x01    // kbd data in buffer
+#define KBDATAP         0x60    // kbd data port(I)
+
+#define NO              0
+
+#define SHIFT           (1<<0)
+#define CTL             (1<<1)
+#define ALT             (1<<2)
+
+#define CAPSLOCK        (1<<3)
+#define NUMLOCK         (1<<4)
+#define SCROLLLOCK      (1<<5)
+
+#define E0ESC           (1<<6)
+
+// Right Alt, tracked apart from left Alt.
+//
+// They used to be the same bit, which is fine for typing -- neither is used to
+// look up a character -- and wrong for chords. On a Polish layout AltGr is how
+// you type a c e l n o s x z with their diacritics, and it is held constantly.
+// Nothing the kernel binds may involve it.
+#define RALT            (1<<7)
+
+// Special keycodes.
+//
+// **Above every Unicode codepoint, deliberately**, and they did not use to be:
+// KBD_UP was 0xE2 and its neighbours filled 0xE0..0xE9. Those are exactly the
+// UTF-8 lead bytes for three-byte characters, so typing any of U+0800..U+FFFF
+// -- which is most punctuation, every arrow, every maths symbol, and the whole
+// of CJK -- produced a keycode the console read as an arrow key and turned
+// into `ESC [ A`. `∞`, `→`, `≤` and `'` all vanished from the input line while
+// `ą` and `ę` came through, because those are two-byte sequences whose lead
+// byte is 0xC4 and nothing claimed 0xC4.
+//
+// The chord codes below already knew this rule and said so; the navigation
+// keys predate them and were never brought in line. The rule, stated once: a
+// value that a key produces is either a Unicode codepoint or it is above
+// 0x10FFFF, and nothing in between means anything.
+#define KBD_SPECIAL     0x110000
+
+#define KBD_HOME        (KBD_SPECIAL + 0x00)
+#define KBD_END         (KBD_SPECIAL + 0x01)
+#define KBD_UP          (KBD_SPECIAL + 0x02)
+#define KBD_DN          (KBD_SPECIAL + 0x03)
+#define KBD_LF          (KBD_SPECIAL + 0x04)
+#define KBD_RT          (KBD_SPECIAL + 0x05)
+#define KBD_PGUP        (KBD_SPECIAL + 0x06)
+#define KBD_PGDN        (KBD_SPECIAL + 0x07)
+#define KBD_INS         (KBD_SPECIAL + 0x08)
+#define KBD_DEL         (KBD_SPECIAL + 0x09)
+
+// Switch virtual terminal.
+//
+// *Which* chord is a runtime setting, not a constant here, and that is the
+// interesting part. Three separate parties have a claim on every candidate:
+//
+//   the HOST, which sees the keystroke first and may never pass it on
+//     Alt+F4, Alt+F2            window manager
+//     Ctrl+Alt+F1..F6           display manager, and it matches loosely --
+//                               adding Shift does not get past it
+//     Ctrl+Alt+<digit>          QEMU's own console tabs
+//
+//   APPLICATIONS, which lose the key permanently if the kernel eats it
+//     Alt+<anything>            Meta. zsh binds Meta-digit as digit-argument
+//     Ctrl+<letter>             control characters
+//     Ctrl+Shift+<digit>        types a character -- Ctrl+Shift+2 is ^@
+//     F1..F6 alone              help, and full-screen programs
+//
+//   the KEYBOARD LAYOUT
+//     AltGr+<letter>            Polish diacritics, and on some setups AltGr
+//                               arrives as Ctrl+Alt
+//
+// There is no combination that is free for everyone on every host, and the
+// guest cannot find out what its host grabs -- the keystroke simply never
+// arrives, which is indistinguishable from a chord nobody pressed. So the
+// kernel ships a default and lets it be changed: VT_SETCHORD, and `chvt -c`
+// in userspace. Setting it to no modifiers disables the chord entirely and
+// leaves `chvt N` as the only way to switch, which is a legitimate choice on
+// a machine whose host takes everything.
+//
+// The default is AltGr+F1..F6, and the "AltGr wants it" line above needs
+// reading carefully: what a Polish layout wants is AltGr+*letter*. AltGr with
+// a function key produces nothing on any layout, no window manager binds it,
+// and no application asks for it. Right Alt being a separate modifier bit
+// here is what makes the distinction expressible at all -- it used to share
+// ALT, which is harmless for typing and useless for this.
+#define KBD_VT_SWITCH   (KBD_SPECIAL + 0x20)
+
+// Previous / next terminal, on the same modifiers as the chord above. The
+// minus and equals keys, which sit together and read as - and + -- a relative
+// move for when you have two terminals and do not care which number they are.
+#define KBD_VT_PREV     (KBD_SPECIAL + 0x30)
+#define KBD_VT_NEXT     (KBD_SPECIAL + 0x31)
+
+#define SCAN_MINUS      0x0C      // - / _
+#define SCAN_EQUALS     0x0D      // = / +
+
+#define SCAN_F1         0x3B      // F1..F6 are scancodes 0x3B..0x40
+#define SCAN_1          0x02      // 1..6 are scancodes 0x02..0x07
+
+// C('A') == Control-A
+#define C(x) (x - '@')
+
+#endif /* KBD_H */