annotate toys/other/oneit.c @ 1776:7bf68329eb3b draft default tip

Repository switched to git at https://github.com/landley/toybox
author Rob Landley <rob@landley.net>
date Thu, 09 Apr 2015 02:28:32 -0500
parents b2b2d214727a
children
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1 /* oneit.c - tiny init replacement to launch a single child process.
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2 *
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3 * Copyright 2005, 2007 by Rob Landley <rob@landley.net>.
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4
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5 USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN))
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6
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7 config ONEIT
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8 bool "oneit"
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9 default y
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10 help
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11 usage: oneit [-p] [-c /dev/tty0] command [...]
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13 Simple init program that runs a single supplied command line with a
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14 controlling tty (so CTRL-C can kill it).
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16 -c Which console device to use (/dev/console doesn't do CTRL-C, etc).
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17 -p Power off instead of rebooting when command exits.
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18 -r Restart child when it exits.
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19 -3 Write 32 bit PID of each exiting reparented process to fd 3 of child.
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20 (Blocking writes, child must read to avoid eventual deadlock.)
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22 Spawns a single child process (because PID 1 has signals blocked)
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23 in its own session, reaps zombies until the child exits, then
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24 reboots the system (or powers off with -p, or restarts the child with -r).
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25 */
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27 #define FOR_oneit
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28 #include "toys.h"
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29 #include <sys/reboot.h>
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31 GLOBALS(
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32 char *console;
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33 )
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34
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35 // The minimum amount of work necessary to get ctrl-c and such to work is:
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36 //
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37 // - Fork a child (PID 1 is special: can't exit, has various signals blocked).
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38 // - Do a setsid() (so we have our own session).
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39 // - In the child, attach stdio to /dev/tty0 (/dev/console is special)
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40 // - Exec the rest of the command line.
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41 //
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42 // PID 1 then reaps zombies until the child process it spawned exits, at which
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43 // point it calls sync() and reboot(). I could stick a kill -1 in there.
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45 // Perform actions in response to signals. (Only root can send us signals.)
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46 static void oneit_signaled(int signal)
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47 {
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48 int action = RB_AUTOBOOT;
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50 toys.signal = signal;
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51 if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
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52 if (signal == SIGUSR2) action = RB_POWER_OFF;
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54 // PID 1 can't call reboot() because it kills the task that calls it,
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55 // which causes the kernel to panic before the actual reboot happens.
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56 sync();
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57 if (!vfork()) reboot(action);
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58 }
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60 void oneit_main(void)
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61 {
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62 int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
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64 if (FLAG_3) {
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65 // Ensure next available filehandle is #3
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66 while (open("/", 0) < 3);
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67 close(3);
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68 close(4);
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69 if (pipe(pipes)) perror_exit("pipe");
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70 fcntl(4, F_SETFD, FD_CLOEXEC);
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71 }
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73 // Setup signal handlers for signals of interest
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74 for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
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76 while (!toys.signal) {
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78 // Create a new child process.
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79 pid = vfork();
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80 if (pid) {
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81
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82 // pid 1 reaps zombies until it gets its child, then halts system.
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83 // We ignore the return value of write (what would we do with it?)
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84 // but save it in a variable we never read to make fortify shut up.
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85 // (Real problem is if pid2 never reads, write() fills pipe and blocks.)
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86 while (pid != wait(&i)) if (FLAG_3) i = write(4, &pid, 4);
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87 if (toys.optflags & FLAG_n) continue;
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88
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89 oneit_signaled((toys.optflags & FLAG_p) ? SIGUSR2 : SIGTERM);
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90 } else {
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91 // Redirect stdio to /dev/tty0, with new session ID, so ctrl-c works.
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92 setsid();
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93 for (i=0; i<3; i++) {
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94 close(i);
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95 // Remember, O_CLOEXEC is backwards for xopen()
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96 xopen(TT.console ? TT.console : "/dev/tty0", O_RDWR|O_CLOEXEC);
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97 }
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98
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99 // Can't xexec() here, we vforked so we don't want to error_exit().
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100 toy_exec(toys.optargs);
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101 execvp(*toys.optargs, toys.optargs);
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102 perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
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103
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104 break;
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105 }
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106 }
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108 // Give reboot() time to kick in, or avoid rapid spinning if exec failed
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109 sleep(5);
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110 _exit(127);
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111 }