. new kernel call sysctl for generic unprivileged system operations;

now used for printing diagnostic messages through the kernel message
   buffer. this lets processes print diagnostics without sending messages
   to tty and log directly, simplifying the message protocol a lot and
   reducing difficulties with deadlocks and other situations in which
   diagnostics are blackholed (e.g. grants don't work). this makes
   DIAGNOSTICS(_S), ASYN_DIAGNOSTICS and DIAG_REPL obsolete, although tty
   and log still accept the codes for 'old' binaries. This also simplifies
   diagnostics in several servers and drivers - only tty needs its own
   kputc() now.
 . simplifications in vfs, and some effort to get the vnode references
   right (consistent) even during shutdown. m_mounted_on is now NULL
   for root filesystems (!) (the original and new root), a less awkward
   special case than 'm_mounted_on == m_root_node'. root now has exactly
   one reference, to root, if no files are open, just like all other
   filesystems. m_driver_e is unused.

kernel/system/Makefile

@@ -43,6 +43,7 @@ OBJECTS	= \
 	$(SYSTEM)(do_privctl.o) \
 	$(SYSTEM)(do_segctl.o) \
 	$(SYSTEM)(do_safecopy.o) \
+	$(SYSTEM)(do_sysctl.o) \
 	$(SYSTEM)(do_getksig.o) \
 	$(SYSTEM)(do_endksig.o) \
 	$(SYSTEM)(do_kill.o) \
@@ -151,6 +152,9 @@ $(SYSTEM)(do_privctl.o):	do_privctl.c
 $(SYSTEM)(do_safecopy.o):	do_safecopy.c
 	$(CC) do_safecopy.c
 
+$(SYSTEM)(do_sysctl.o):	do_sysctl.c
+	$(CC) do_sysctl.c
+
 $(SYSTEM)(do_segctl.o):	do_segctl.c
 	$(CC) do_segctl.c