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Sometimes there's a need to figure out the controlling tty from a shell script, for example, to obtain a line for getty. In this case it's easier to call cttyhack than trying to repeat some of the cttyhack's logic. function old new delta cttyhack_main 283 327 +44 packed_usage 28911 28915 +4 Signed-off-by: Alexander Shishkin <virtuoso@slind.org> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
177 lines
5.1 KiB
C
177 lines
5.1 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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#include "libbb.h"
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//applet:IF_CTTYHACK(APPLET(cttyhack, BB_DIR_BIN, BB_SUID_DROP))
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//kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
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//config:config CTTYHACK
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//config: bool "cttyhack"
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//config: default y
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//config: help
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//config: One common problem reported on the mailing list is the "can't
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//config: access tty; job control turned off" error message, which typically
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//config: appears when one tries to use a shell with stdin/stdout on
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//config: /dev/console.
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//config: This device is special - it cannot be a controlling tty.
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//config:
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//config: The proper solution is to use the correct device instead of
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//config: /dev/console.
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//config:
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//config: cttyhack provides a "quick and dirty" solution to this problem.
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//config: It analyzes stdin with various ioctls, trying to determine whether
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//config: it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
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//config: On Linux it also checks sysfs for a pointer to the active console.
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//config: If cttyhack is able to find the real console device, it closes
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//config: stdin/out/err and reopens that device.
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//config: Then it executes the given program. Opening the device will make
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//config: that device a controlling tty. This may require cttyhack
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//config: to be a session leader.
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//config:
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//config: Example for /etc/inittab (for busybox init):
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//config:
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//config: ::respawn:/bin/cttyhack /bin/sh
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//config:
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//config: Starting an interactive shell from boot shell script:
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//config:
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//config: setsid cttyhack sh
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//config:
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//config: Giving controlling tty to shell running with PID 1:
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//config:
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//config: # exec cttyhack sh
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//config:
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//config: Without cttyhack, you need to know exact tty name,
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//config: and do something like this:
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//config:
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//config: # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
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//config:
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//config: Starting getty on a controlling tty from a shell script:
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//config:
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//config: # getty 115200 $(cttyhack)
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//usage:#define cttyhack_trivial_usage
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//usage: "[PROG ARGS]"
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//usage:#define cttyhack_full_usage "\n\n"
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//usage: "Give PROG a controlling tty if possible."
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//usage: "\nExample for /etc/inittab (for busybox init):"
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//usage: "\n ::respawn:/bin/cttyhack /bin/sh"
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//usage: "\nGiving controlling tty to shell running with PID 1:"
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//usage: "\n $ exec cttyhack sh"
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//usage: "\nStarting interactive shell from boot shell script:"
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//usage: "\n setsid cttyhack sh"
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#if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
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# warning cttyhack will not be able to detect a controlling tty on this system
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#endif
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/* From <linux/vt.h> */
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struct vt_stat {
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unsigned short v_active; /* active vt */
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unsigned short v_signal; /* signal to send */
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unsigned short v_state; /* vt bitmask */
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};
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enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
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/* From <linux/serial.h> */
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struct serial_struct {
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int type;
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int line;
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unsigned int port;
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int irq;
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int flags;
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int xmit_fifo_size;
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int custom_divisor;
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int baud_base;
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unsigned short close_delay;
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char io_type;
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char reserved_char[1];
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int hub6;
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unsigned short closing_wait; /* time to wait before closing */
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unsigned short closing_wait2; /* no longer used... */
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unsigned char *iomem_base;
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unsigned short iomem_reg_shift;
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unsigned int port_high;
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unsigned long iomap_base; /* cookie passed into ioremap */
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int reserved[1];
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};
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int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int cttyhack_main(int argc UNUSED_PARAM, char **argv)
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{
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int fd;
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char console[sizeof(int)*3 + 16];
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union {
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struct vt_stat vt;
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struct serial_struct sr;
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char paranoia[sizeof(struct serial_struct) * 3];
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} u;
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strcpy(console, "/dev/tty");
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fd = open(console, O_RDWR);
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if (fd < 0) {
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/* We don't have ctty (or don't have "/dev/tty" node...) */
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do {
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#ifdef __linux__
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int s;
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if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
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/* this is linux virtual tty */
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sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active);
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break;
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}
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#endif
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#ifdef TIOCGSERIAL
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if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
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/* this is a serial console; assuming it is named /dev/ttySn */
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sprintf(console + 8, "S%u", (int)u.sr.line);
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break;
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}
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#endif
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#ifdef __linux__
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/* Note that this method is not related to _stdin_ */
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s = open_read_close("/sys/class/tty/console/active",
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console + 5, sizeof(console) - 5);
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if (s > 0) {
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/* found active console via sysfs (Linux 2.6.38+)
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* sysfs string looks like "ttyS0\n" so zap the newline:
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*/
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console[4 + s] = '\0';
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break;
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}
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#endif
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/* nope, could not find it */
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console[0] = '\0';
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} while (0);
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}
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argv++;
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if (!argv[0]) {
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if (!console[0])
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return EXIT_FAILURE;
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puts(console);
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return EXIT_SUCCESS;
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}
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if (fd < 0) {
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fd = open_or_warn(console, O_RDWR);
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if (fd < 0)
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goto ret;
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}
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//bb_error_msg("switching to '%s'", console);
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dup2(fd, 0);
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dup2(fd, 1);
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dup2(fd, 2);
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while (fd > 2)
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close(fd--);
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/* Some other session may have it as ctty,
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* try to steal it from them:
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*/
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ioctl(0, TIOCSCTTY, 1);
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ret:
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BB_EXECVP_or_die(argv);
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}
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