cttyhack: move build system bits into cttyhack.c, no code changes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/cttyhack.c

@@ -6,6 +6,58 @@
  */
 #include "libbb.h"
 
+//applet:IF_CTTYHACK(APPLET(cttyhack, _BB_DIR_BIN, _BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
+
+//config:config CTTYHACK
+//config:	bool "cttyhack"
+//config:	default y
+//config:	help
+//config:	  One common problem reported on the mailing list is "can't access tty;
+//config:	  job control turned off" error message which typically appears when
+//config:	  one tries to use shell with stdin/stdout opened to /dev/console.
+//config:	  This device is special - it cannot be a controlling tty.
+//config:
+//config:	  Proper solution is to use correct device instead of /dev/console.
+//config:
+//config:	  cttyhack provides "quick and dirty" solution to this problem.
+//config:	  It analyzes stdin with various ioctls, trying to determine whether
+//config:	  it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
+//config:	  If it detects one, it closes stdin/out/err and reopens that device.
+//config:	  Then it executes given program. Opening the device will make
+//config:	  that device a controlling tty. This may require cttyhack
+//config:	  to be a session leader.
+//config:
+//config:	  Example for /etc/inittab (for busybox init):
+//config:
+//config:	  ::respawn:/bin/cttyhack /bin/sh
+//config:
+//config:	  Starting an interactive shell from boot shell script:
+//config:
+//config:	  setsid cttyhack sh
+//config:
+//config:	  Giving controlling tty to shell running with PID 1:
+//config:
+//config:	  # exec cttyhack sh
+//config:
+//config:	  Without cttyhack, you need to know exact tty name,
+//config:	  and do something like this:
+//config:
+//config:	  # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
+//config:
+
+//usage:#define cttyhack_trivial_usage
+//usage:       "PROG ARGS"
+//usage:#define cttyhack_full_usage "\n\n"
+//usage:       "Give PROG a controlling tty if possible."
+//usage:     "\nExample for /etc/inittab (for busybox init):"
+//usage:     "\n	::respawn:/bin/cttyhack /bin/sh"
+//usage:     "\nGiving controlling tty to shell running with PID 1:"
+//usage:     "\n	$ exec cttyhack sh"
+//usage:     "\nStarting interactive shell from boot shell script:"
+//usage:     "\n	setsid cttyhack sh"
+
 /* From <linux/vt.h> */
 struct vt_stat {
 	unsigned short v_active;        /* active vt */