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/core/defs.h

@@ -546,6 +546,7 @@ int             sockbind_in(struct socket*, uint addr, ushort port);
 int             sockconnect_in(struct socket*, uint addr, ushort port);
 int             sock_domain(struct socket*);
 int             sock_peercred(struct socket*, int*, uint*, uint*);
+int             sock_passcred(struct socket*);
 // Socket options. The syscall layer does the user-memory marshalling and these
 // do the work, because struct socket's fields live in kernel/net/unix.c and the
 // syscall layer deliberately cannot see them.
@@ -733,6 +734,7 @@ int             net_eth_detach(struct device *);
 int             net_detach(struct device *);
 int             net_attach_late(struct device *);
 int             net_eth_poll(void);
+void            net_eth_link_check(void);
 int             net_eth_count(void);
 void            net_eth_counts(int i, uint64 *rx, uint64 *tx);
 struct netif   *net_eth_netif(int i);
@@ -805,6 +807,8 @@ void            inotify_file(struct file *f, uint32 mask);
 uint32          inotify_cookie(void);
 int             ev_fionread(struct evobj *o);
 int             pipe_avail(struct pipe *p);
+int             vm_fault(addr_t va);
+pte_t*          walkpte(pml4e_t *pgdir, const void *va);
 int             path_identity(char *path, int follow, int onlydir, uint *dev, uint64 *inum);
 int             memfd_rw(int id, int user, uint64 buf, uint64 off, int n, int writing);
 void            shm_detach(int id);

include/dev/kbd.h

@@ -92,12 +92,10 @@
 // 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.
+// The default is Ctrl+Alt+F1..F12: the keys X switches with, so the console
+// and the desktop answer the same chord. It used to be AltGr+F-key, which
+// nothing else claims -- Right Alt being a separate modifier bit here is what
+// makes that expressible, and `chvt -c altgr+F` still sets it.
 #define KBD_VT_SWITCH   (KBD_SPECIAL + 0x20)
 
 // Previous / next terminal, on the same modifiers as the chord above. The

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.
 //

include/net/socket.h

@@ -349,6 +349,7 @@ struct socket {
   int   o_keepalive;
   int   o_broadcast;
   int   o_nodelay;
+  int   o_passcred;   // SO_PASSCRED: SCM_CREDENTIALS on every recvmsg
 
   // Descriptors sent to this socket and not yet received. They live on the
   // *receiving* side, next to the bytes they were sent with, because that is

include/uapi/posix.h

@@ -432,6 +432,7 @@ struct statfs {
 #define MAP_PRIVATE   0x02
 #define MAP_FIXED     0x10
 #define MAP_ANONYMOUS 0x20
+#define MAP_NORESERVE 0x4000
 
 // waitpid() options. The kernel tests `options & 1`; this is that bit, named.
 #define WNOHANG   0x001