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

kernel/core/console.c

@@ -336,7 +336,7 @@ static struct spinlock input_lock;
 //    1        /dev/console   the active terminal, so kernel messages and a
 //                            shell started on the console both follow a switch
 //    10       /dev/tty       the caller's controlling terminal
-//    11..16   /dev/tty1..6   that terminal, whether or not it is on screen
+//    11..22   /dev/tty1..12  that terminal, whether or not it is on screen
 //
 // Anything else is the console, which is what an unrecognised minor meant
 // before there was more than one terminal to get wrong.
@@ -461,7 +461,7 @@ erase_one(struct vt *v)
 // Keyboard input
 // ---------------------------------------------------------------------------
 
-// Alt+F1..F6, Ctrl+Alt+F1..F6 and the settable chord (AltGr+F1..F6 by
+// Alt+F-key, Ctrl+Alt+F-key and the settable chord (Ctrl+Alt+F1..F12 by
 // default) switch terminals. kbd.c reports them as
 // KBD_VT_SWITCH+n so that the
 // decision of what a chord *means* is made here, where the terminals are,