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

cmd/chvt/main.c

@@ -19,13 +19,14 @@
 // guest cannot detect this: a key the host swallowed is indistinguishable from
 // a key nobody pressed. So it is a setting.
 //
-//   chvt -c altgr+F           AltGr+F1..F6        (the default)
-//   chvt -c ctrl+shift+F      Ctrl+Shift+F1..F6
-//   chvt -c alt+1             Alt+1..6
+//   chvt -c ctrl+alt+F        Ctrl+Alt+F1..F12    (the default)
+//   chvt -c altgr+F           AltGr+F1..F12
+//   chvt -c ctrl+shift+F      Ctrl+Shift+F1..F12
+//   chvt -c alt+1             Alt+1..9
 //   chvt -c off               no chord at all
 //
 // Whatever the modifiers are, they also bind minus and equals to the previous
-// and next terminal in use -- AltGr+- and AltGr+= by default.
+// and next terminal in use -- Ctrl+Alt+- and Ctrl+Alt+= by default.
 
 #include "core/types.h"
 #include "uapi/user.h"