/* vi: set sw=4 ts=4: */
/*
- * Licensed under GPLv2
- *
* Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
*/
#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 the "can't
+//config: access tty; job control turned off" error message, which typically
+//config: appears when one tries to use a shell with stdin/stdout on
+//config: /dev/console.
+//config: This device is special - it cannot be a controlling tty.
+//config:
+//config: The proper solution is to use the correct device instead of
+//config: /dev/console.
+//config:
+//config: cttyhack provides a "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: On Linux it also checks sysfs for a pointer to the active console.
+//config: If cttyhack is able to find the real console device, it closes
+//config: stdin/out/err and reopens that device.
+//config: Then it executes the 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:
+//config: Starting getty on a controlling tty from a shell script:
+//config:
+//config: # getty 115200 $(cttyhack)
+
+//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"
+
+#if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
+# warning cttyhack will not be able to detect a controlling tty on this system
+#endif
+
/* From <linux/vt.h> */
struct vt_stat {
unsigned short v_active; /* active vt */
};
int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int cttyhack_main(int argc ATTRIBUTE_UNUSED, char **argv)
+int cttyhack_main(int argc UNUSED_PARAM, char **argv)
{
int fd;
char console[sizeof(int)*3 + 16];
char paranoia[sizeof(struct serial_struct) * 3];
} u;
- if (!*++argv) {
- bb_show_usage();
- }
-
strcpy(console, "/dev/tty");
- if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
- /* this is a serial console */
- sprintf(console + 8, "S%d", u.sr.line);
- } else if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
- /* this is linux virtual tty */
- sprintf(console + 8, "S%d" + 1, u.vt.v_active);
+ fd = open(console, O_RDWR);
+ if (fd < 0) {
+ /* We don't have ctty (or don't have "/dev/tty" node...) */
+ do {
+#ifdef __linux__
+ /* Note that this method does not use _stdin_.
+ * Thus, "cttyhack </dev/something" can't be used.
+ * However, this method is more reliable than
+ * TIOCGSERIAL check, which assumes that all
+ * serial lines follow /dev/ttySn convention -
+ * which is not always the case.
+ * Therefore, we use this method first:
+ */
+ int s = open_read_close("/sys/class/tty/console/active",
+ console + 5, sizeof(console) - 5);
+ if (s > 0) {
+ char *last;
+ /* Found active console via sysfs (Linux 2.6.38+).
+ * It looks like "[tty0 ]ttyS0\n" so zap the newline:
+ */
+ console[4 + s] = '\0';
+ /* If there are multiple consoles,
+ * take the last one:
+ */
+ last = strrchr(console + 5, ' ');
+ if (last)
+ overlapping_strcpy(console + 5, last + 1);
+ break;
+ }
+
+ if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
+ /* this is linux virtual tty */
+ sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active);
+ break;
+ }
+#endif
+#ifdef TIOCGSERIAL
+ if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
+ /* this is a serial console; assuming it is named /dev/ttySn */
+ sprintf(console + 8, "S%u", (int)u.sr.line);
+ break;
+ }
+#endif
+ /* nope, could not find it */
+ console[0] = '\0';
+ } while (0);
}
- if (console[8]) {
- fd = xopen(console, O_RDWR);
- //bb_error_msg("switching to '%s'", console);
- dup2(fd, 0);
- dup2(fd, 1);
- dup2(fd, 2);
- while (fd > 2) close(fd--);
- /* Some other session may have it as ctty. Steal it from them */
- ioctl(0, TIOCSCTTY, 1);
+ argv++;
+ if (!argv[0]) {
+ if (!console[0])
+ return EXIT_FAILURE;
+ puts(console);
+ return EXIT_SUCCESS;
}
- BB_EXECVP(argv[0], argv);
- bb_perror_msg_and_die("cannot exec '%s'", argv[0]);
+ if (fd < 0) {
+ fd = open_or_warn(console, O_RDWR);
+ if (fd < 0)
+ goto ret;
+ }
+ //bb_error_msg("switching to '%s'", console);
+ dup2(fd, 0);
+ dup2(fd, 1);
+ dup2(fd, 2);
+ while (fd > 2)
+ close(fd--);
+ /* Some other session may have it as ctty,
+ * try to steal it from them:
+ */
+ ioctl(0, TIOCSCTTY, 1);
+ ret:
+ BB_EXECVP_or_die(argv);
}
projects / oweals / busybox.git / blobdiff