Demand paging, the RTL8168H, links that come up late, and Ctrl+Alt+F1..F12

- Anonymous memory can be reserved without being backed: large mappings,
  MAP_NORESERVE and PROT_NONE are recorded and each page appears, zeroed,
  on first touch -- from trap() for the program, from uva2ka() for the
  kernel on its behalf. WebKit reserves 4 GB at start and touches a sliver;
  backing it all failed with ENOMEM and Epiphany aborted.
- r8169: the 8168G generation and later (the laptop's 8168H, XID 541) are
  taken from the firmware's out-of-band mode, get their PLL powered, the
  receive gate opened, and their PHY reached through the OCP window. The
  PHY's power-down bit is cleared; the old code kept it while restarting
  autonegotiation. Untested on the hardware so far.
- The network thread follows each device's link into lwIP. The link was
  read once at attach, 0.02 s into boot; real autonegotiation takes
  seconds, so on hardware the interface stayed down for good.
- Twelve terminals, switched with Ctrl+Alt+F1..F12 by default: the keys X
  uses, so the console and the desktop agree. AltGr+F-key is gone from
  the defaults (chvt -c altgr+F brings it back).
- SO_PASSCRED on Unix sockets, with SCM_CREDENTIALS delivered by recvmsg.
  WebKit sets it on its IPC sockets and aborted when refused.

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

docs/architecture/terminals.md

@@ -1,12 +1,13 @@
 <!-- SPDX-License-Identifier: GPL-2.0-or-later -->
 # Virtual terminals
 
-Six of them, `/dev/tty1` through `/dev/tty6`.
+Twelve of them, `/dev/tty1` through `/dev/tty12`, one per function key.
 
 | | |
 |---|---|
-| **AltGr+F1 .. F6** | go to that terminal |
-| **AltGr+-** / **AltGr+=** | previous / next terminal *in use* |
+| **Ctrl+Alt+F1 .. F12** | go to that terminal — on the console and under X alike |
+| **Alt+F1 .. F12** | the same, on the text console only (X keeps plain Alt) |
+| **Ctrl+Alt+-** / **Ctrl+Alt+=** | previous / next terminal *in use* |
 | `chvt N` | the same, from a script or a serial console |
 
 The chord is settable — `chvt -c` — for the reasons below. Each one is an independent terminal: its own screen, its own
@@ -14,8 +15,9 @@ cursor, its own line discipline, its own foreground process group and its own
 session. Two shells on two terminals are two unrelated processes that happen to
 share a keyboard and a screen.
 
-A seventh is deliberately not bound. That is where a display server goes,
-and it will claim switching with `VT_SETMODE` rather than a chord.
+A display server takes one of them with `VT_SETMODE` and does its own
+switching; X switches with Ctrl+Alt+F-key, which is why that is the default
+here too.
 
 ---
 
@@ -202,8 +204,9 @@ So the kernel ships a default and lets it be moved:
 
 ```sh
 chvt                        # report the active terminal and the current chord
-chvt -c altgr+F             # AltGr+F1..F6        (the default)
-chvt -c ctrl+shift+F        # Ctrl+Shift+F1..F6
+chvt -c ctrl+alt+F          # Ctrl+Alt+F1..F12    (the default)
+chvt -c altgr+F             # AltGr+F1..F12       (the default until 2026-10)
+chvt -c ctrl+shift+F        # Ctrl+Shift+F1..F12
 chvt -c alt+1               # Alt+1..6
 chvt -c off                 # no chord; chvt N is then the only way
 ```
@@ -211,23 +214,23 @@ chvt -c off                 # no chord; chvt N is then the only way
 `off` is a legitimate setting, not a failure mode. On a machine whose host
 grabs everything worth binding, `chvt N` from a shell is the honest answer.
 
-The default is **AltGr+F1..F6**, and the `AltGr+`letter row above needs reading
-carefully: what a Polish layout wants is AltGr with a **letter**. AltGr with a
-**function key** produces nothing on any layout, no window manager binds it,
-and no application asks for it. It is the one combination all three parties
-leave alone.
+The default is **Ctrl+Alt+F1..F12**. It was AltGr+F-key for a long time —
+AltGr with a **function key** produces nothing on any layout, no window manager
+binds it, and no application asks for it — but X owns the keyboard while it
+runs and switches only with Ctrl+Alt+F-key, so the console and the desktop
+answered different keys for the same thing. One chord everywhere wins. Inside
+a VM whose host grabs Ctrl+Alt+F-key, `chvt -c altgr+F` brings the old one
+back.
 
 That distinction is only expressible because Right Alt is tracked as its own
 modifier bit. It used to share `ALT`, which is harmless for typing — neither is
 used to look up a character — and made this impossible to say.
 
-Verified rather than argued: with the default set, `AltGr+F2` switches,
-`AltGr+F1` returns to a pixel-identical tty1, and `AltGr+a` still reaches the
-shell, so ą is untouched.
+AltGr+letter still reaches the shell untouched, so ą is unaffected either way.
 
 Whatever the modifiers are, they also bind **minus** and **equals** to the
 previous and next terminal. Those step only through terminals that are *in
-use* — the same `opened` count `VT_GETSTATE` reports — because six terminals
+use* — the same `opened` count `VT_GETSTATE` reports — because twelve terminals
 with two shells on them means four blank screens in between, and cycling past
 them is worse than not having the key.