[2725] | 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
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[1765] | 4 | *
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[2725] | 5 | * Licensed under GPLv2, see file LICENSE in this source tree.
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[1765] | 6 | */
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| 7 | #include "libbb.h"
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| 8 |
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[3232] | 9 | //applet:IF_CTTYHACK(APPLET(cttyhack, BB_DIR_BIN, BB_SUID_DROP))
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[2725] | 10 |
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| 11 | //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
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| 12 |
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| 13 | //config:config CTTYHACK
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| 14 | //config: bool "cttyhack"
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| 15 | //config: default y
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| 16 | //config: help
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[3232] | 17 | //config: One common problem reported on the mailing list is the "can't
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| 18 | //config: access tty; job control turned off" error message, which typically
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| 19 | //config: appears when one tries to use a shell with stdin/stdout on
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| 20 | //config: /dev/console.
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[2725] | 21 | //config: This device is special - it cannot be a controlling tty.
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| 22 | //config:
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[3232] | 23 | //config: The proper solution is to use the correct device instead of
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| 24 | //config: /dev/console.
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[2725] | 25 | //config:
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[3232] | 26 | //config: cttyhack provides a "quick and dirty" solution to this problem.
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[2725] | 27 | //config: It analyzes stdin with various ioctls, trying to determine whether
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| 28 | //config: it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
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[3232] | 29 | //config: On Linux it also checks sysfs for a pointer to the active console.
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| 30 | //config: If cttyhack is able to find the real console device, it closes
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| 31 | //config: stdin/out/err and reopens that device.
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| 32 | //config: Then it executes the given program. Opening the device will make
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[2725] | 33 | //config: that device a controlling tty. This may require cttyhack
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| 34 | //config: to be a session leader.
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| 35 | //config:
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| 36 | //config: Example for /etc/inittab (for busybox init):
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| 37 | //config:
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| 38 | //config: ::respawn:/bin/cttyhack /bin/sh
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| 39 | //config:
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| 40 | //config: Starting an interactive shell from boot shell script:
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| 41 | //config:
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| 42 | //config: setsid cttyhack sh
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| 43 | //config:
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| 44 | //config: Giving controlling tty to shell running with PID 1:
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| 45 | //config:
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| 46 | //config: # exec cttyhack sh
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| 47 | //config:
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| 48 | //config: Without cttyhack, you need to know exact tty name,
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| 49 | //config: and do something like this:
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| 50 | //config:
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| 51 | //config: # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
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| 52 | //config:
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[3232] | 53 | //config: Starting getty on a controlling tty from a shell script:
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| 54 | //config:
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| 55 | //config: # getty 115200 $(cttyhack)
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[2725] | 56 |
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| 57 | //usage:#define cttyhack_trivial_usage
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[3232] | 58 | //usage: "[PROG ARGS]"
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[2725] | 59 | //usage:#define cttyhack_full_usage "\n\n"
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| 60 | //usage: "Give PROG a controlling tty if possible."
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| 61 | //usage: "\nExample for /etc/inittab (for busybox init):"
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| 62 | //usage: "\n ::respawn:/bin/cttyhack /bin/sh"
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| 63 | //usage: "\nGiving controlling tty to shell running with PID 1:"
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| 64 | //usage: "\n $ exec cttyhack sh"
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| 65 | //usage: "\nStarting interactive shell from boot shell script:"
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| 66 | //usage: "\n setsid cttyhack sh"
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| 67 |
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| 68 | #if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
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| 69 | # warning cttyhack will not be able to detect a controlling tty on this system
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| 70 | #endif
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| 71 |
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[1765] | 72 | /* From <linux/vt.h> */
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| 73 | struct vt_stat {
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[2725] | 74 | unsigned short v_active; /* active vt */
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| 75 | unsigned short v_signal; /* signal to send */
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| 76 | unsigned short v_state; /* vt bitmask */
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[1765] | 77 | };
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[2725] | 78 | enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
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[1765] | 79 |
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| 80 | /* From <linux/serial.h> */
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| 81 | struct serial_struct {
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| 82 | int type;
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| 83 | int line;
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| 84 | unsigned int port;
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| 85 | int irq;
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| 86 | int flags;
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| 87 | int xmit_fifo_size;
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| 88 | int custom_divisor;
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| 89 | int baud_base;
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| 90 | unsigned short close_delay;
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| 91 | char io_type;
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| 92 | char reserved_char[1];
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| 93 | int hub6;
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[2725] | 94 | unsigned short closing_wait; /* time to wait before closing */
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| 95 | unsigned short closing_wait2; /* no longer used... */
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[1765] | 96 | unsigned char *iomem_base;
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| 97 | unsigned short iomem_reg_shift;
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| 98 | unsigned int port_high;
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| 99 | unsigned long iomap_base; /* cookie passed into ioremap */
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| 100 | int reserved[1];
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| 101 | };
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| 102 |
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[2725] | 103 | int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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| 104 | int cttyhack_main(int argc UNUSED_PARAM, char **argv)
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[1765] | 105 | {
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| 106 | int fd;
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| 107 | char console[sizeof(int)*3 + 16];
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| 108 | union {
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| 109 | struct vt_stat vt;
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| 110 | struct serial_struct sr;
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| 111 | char paranoia[sizeof(struct serial_struct) * 3];
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| 112 | } u;
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| 113 |
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| 114 | strcpy(console, "/dev/tty");
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[2725] | 115 | fd = open(console, O_RDWR);
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[3232] | 116 | if (fd < 0) {
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[2725] | 117 | /* We don't have ctty (or don't have "/dev/tty" node...) */
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[3232] | 118 | do {
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| 119 | #ifdef __linux__
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| 120 | /* Note that this method does not use _stdin_.
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| 121 | * Thus, "cttyhack </dev/something" can't be used.
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| 122 | * However, this method is more reliable than
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| 123 | * TIOCGSERIAL check, which assumes that all
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| 124 | * serial lines follow /dev/ttySn convention -
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| 125 | * which is not always the case.
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| 126 | * Therefore, we use this method first:
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| 127 | */
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| 128 | int s = open_read_close("/sys/class/tty/console/active",
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| 129 | console + 5, sizeof(console) - 5);
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| 130 | if (s > 0) {
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| 131 | char *last;
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| 132 | /* Found active console via sysfs (Linux 2.6.38+).
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| 133 | * It looks like "[tty0 ]ttyS0\n" so zap the newline:
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| 134 | */
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| 135 | console[4 + s] = '\0';
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| 136 | /* If there are multiple consoles,
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| 137 | * take the last one:
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| 138 | */
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| 139 | last = strrchr(console + 5, ' ');
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| 140 | if (last)
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| 141 | overlapping_strcpy(console + 5, last + 1);
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| 142 | break;
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| 143 | }
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| 144 |
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| 145 | if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
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| 146 | /* this is linux virtual tty */
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| 147 | sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active);
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| 148 | break;
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| 149 | }
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| 150 | #endif
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[2725] | 151 | #ifdef TIOCGSERIAL
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[3232] | 152 | if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
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| 153 | /* this is a serial console; assuming it is named /dev/ttySn */
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| 154 | sprintf(console + 8, "S%u", (int)u.sr.line);
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| 155 | break;
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| 156 | }
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[2725] | 157 | #endif
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[3232] | 158 | /* nope, could not find it */
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| 159 | console[0] = '\0';
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| 160 | } while (0);
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[1765] | 161 | }
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| 162 |
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[3232] | 163 | argv++;
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| 164 | if (!argv[0]) {
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| 165 | if (!console[0])
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| 166 | return EXIT_FAILURE;
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| 167 | puts(console);
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| 168 | return EXIT_SUCCESS;
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| 169 | }
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| 170 |
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| 171 | if (fd < 0) {
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| 172 | fd = open_or_warn(console, O_RDWR);
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| 173 | if (fd < 0)
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| 174 | goto ret;
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| 175 | }
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| 176 | //bb_error_msg("switching to '%s'", console);
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| 177 | dup2(fd, 0);
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| 178 | dup2(fd, 1);
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| 179 | dup2(fd, 2);
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| 180 | while (fd > 2)
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| 181 | close(fd--);
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| 182 | /* Some other session may have it as ctty,
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| 183 | * try to steal it from them:
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| 184 | */
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| 185 | ioctl(0, TIOCSCTTY, 1);
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| 186 | ret:
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[2725] | 187 | BB_EXECVP_or_die(argv);
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[1765] | 188 | }
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