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

include/dev/vt.h

@@ -26,10 +26,10 @@
 #include "core/param.h"
 #include "uapi/posix.h"
 
-// Six, and Linux's numbering: /dev/tty1 through /dev/tty6, reached with
-// Alt+1..Alt+6. A seventh is deliberately not bound -- that is where a
-// display server goes, and Schcom will want it.
-#define NVT 6
+// Twelve, one per function key, and Linux's numbering: /dev/tty1 through
+// /dev/tty12, reached with Ctrl+Alt+F1..F12 (and plain Alt on the text
+// console). The key codes leave room for sixteen; see KBD_VT_SWITCH.
+#define NVT 12
 
 // A cell.
 //