init.c

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/* This process is the father (mother) of all Minix user processes.  When
 * Minix comes up, this is process number 2, and has a pid of 1.  It
 * executes the /etc/rc shell file, and then reads the /etc/ttytab file to
 * determine which terminals need a login process.
 *
 * If the files /usr/adm/wtmp and /etc/utmp exist and are writable, init
 * (with help from login) will maintain login accounting.  Sending a
 * signal 1 (SIGHUP) to init will cause it to rescan /etc/ttytab and start
 * up new shell processes if necessary.  It will not, however, kill off
 * login processes for lines that have been turned off; do this manually.
 * Signal 15 (SIGTERM) makes init stop spawning new processes, this is
 * used by shutdown and friends when they are about to close the system
 * down.
 */

#include <minix/type.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/svrctl.h>
#include <ttyent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <string.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <utmp.h>

/* Command to execute as a response to the three finger salute. */
char *REBOOT_CMD[] =    { "shutdown", "now", "CTRL-ALT-DEL", NULL };

/* Associated fake ttytab entry. */
struct ttyent TT_REBOOT = { "console", "-", REBOOT_CMD, NULL };

char PATH_UTMP[] = "/etc/utmp";         /* current logins */
char PATH_WTMP[] = "/usr/adm/wtmp";     /* login/logout history */

#define PIDSLOTS        32              /* first this many ttys can be on */

struct slotent {
  int errct;                    /* error count */
  pid_t pid;                    /* pid of login process for this tty line */
};

#define ERRCT_DISABLE   10      /* disable after this many errors */
#define NO_PID  0               /* pid value indicating no process */

struct slotent slots[PIDSLOTS]; /* init table of ttys and pids */

int gothup = 0;                 /* flag, showing signal 1 was received */
int gotabrt = 0;                /* flag, showing signal 6 was received */
int spawn = 1;                  /* flag, spawn processes only when set */

void tell(int fd, char *s);
void report(int fd, char *label);
void wtmp(int type, int linenr, char *line, pid_t pid);
void startup(int linenr, struct ttyent *ttyp);
int execute(char **cmd);
void onhup(int sig);
void onterm(int sig);
void onabrt(int sig);

int main(void)
{
  pid_t pid;                    /* pid of child process */
  int fd;                       /* generally useful */
  int linenr;                   /* loop variable */
  int check;                    /* check if a new process must be spawned */
  struct slotent *slotp;        /* slots[] pointer */
  struct ttyent *ttyp;          /* ttytab entry */
  struct sigaction sa;
  struct stat stb;

  if (fstat(0, &stb) < 0) {
        /* Open standard input, output & error. */
        (void) open("/dev/null", O_RDONLY);
        (void) open("/dev/log", O_WRONLY);
        dup(1);
  }

  sigemptyset(&sa.sa_mask);
  sa.sa_flags = 0;

  /* Hangup: Reexamine /etc/ttytab for newly enabled terminal lines. */
  sa.sa_handler = onhup;
  sigaction(SIGHUP, &sa, NULL);

  /* Terminate: Stop spawning login processes, shutdown is near. */
  sa.sa_handler = onterm;
  sigaction(SIGTERM, &sa, NULL);

  /* Abort: Sent by the kernel on CTRL-ALT-DEL; shut the system down. */
  sa.sa_handler = onabrt;
  sigaction(SIGABRT, &sa, NULL);

  /* Execute the /etc/rc file. */
  if ((pid = fork()) != 0) {
        /* Parent just waits. */
        while (wait(NULL) != pid) {
                if (gotabrt) reboot(RBT_HALT);
        }
  } else {
#if ! SYS_GETKENV
        struct sysgetenv sysgetenv;
#endif
        char bootopts[16];
        static char *rc_command[] = { "sh", "/etc/rc", NULL, NULL, NULL };
        char **rcp = rc_command + 2;

        /* Get the boot options from the boot environment. */
        sysgetenv.key = "bootopts";
        sysgetenv.keylen = 8+1;
        sysgetenv.val = bootopts;
        sysgetenv.vallen = sizeof(bootopts);
        if (svrctl(MMGETPARAM, &sysgetenv) == 0) *rcp++ = bootopts;
        *rcp = "start";

        execute(rc_command);
        report(2, "sh /etc/rc");
        _exit(1);       /* impossible, we hope */
  }

  /* Clear /etc/utmp if it exists. */
  if ((fd = open(PATH_UTMP, O_WRONLY | O_TRUNC)) >= 0) close(fd);

  /* Log system reboot. */
  wtmp(BOOT_TIME, 0, NULL, 0);

  /* Main loop. If login processes have already been started up, wait for one
   * to terminate, or for a HUP signal to arrive. Start up new login processes
   * for all ttys which don't have them. Note that wait() also returns when
   * somebody's orphan dies, in which case ignore it.  If the TERM signal is
   * sent then stop spawning processes, shutdown time is near.
   */

  check = 1;
  while (1) {
        while ((pid = waitpid(-1, NULL, check ? WNOHANG : 0)) > 0) {
                /* Search to see which line terminated. */
                for (linenr = 0; linenr < PIDSLOTS; linenr++) {
                        slotp = &slots[linenr];
                        if (slotp->pid == pid) {
                                /* Record process exiting. */
                                wtmp(DEAD_PROCESS, linenr, NULL, pid);
                                slotp->pid = NO_PID;
                                check = 1;
                        }
                }
        }

        /* If a signal 1 (SIGHUP) is received, simply reset error counts. */
        if (gothup) {
                gothup = 0;
                for (linenr = 0; linenr < PIDSLOTS; linenr++) {
                        slots[linenr].errct = 0;
                }
                check = 1;
        }

        /* Shut down on signal 6 (SIGABRT). */
        if (gotabrt) {
                gotabrt = 0;
                startup(0, &TT_REBOOT);
        }

        if (spawn && check) {
                /* See which lines need a login process started up. */
                for (linenr = 0; linenr < PIDSLOTS; linenr++) {
                        slotp = &slots[linenr];
                        if ((ttyp = getttyent()) == NULL) break;

                        if (ttyp->ty_getty != NULL
                                && ttyp->ty_getty[0] != NULL
                                && slotp->pid == NO_PID
                                && slotp->errct < ERRCT_DISABLE)
                        {
                                startup(linenr, ttyp);
                        }
                }
                endttyent();
        }
        check = 0;
  }
}

void onhup(int sig)
{
  gothup = 1;
  spawn = 1;
}

void onterm(int sig)
{
  spawn = 0;
}

void onabrt(int sig)
{
  static int count;

  if (++count == 2) reboot(RBT_HALT);
  gotabrt = 1;
}

void startup(int linenr, struct ttyent *ttyp)
{
  /* Fork off a process for the indicated line. */

  struct slotent *slotp;                /* pointer to ttyslot */
  pid_t pid;                            /* new pid */
  int err[2];                           /* error reporting pipe */
  char line[32];                        /* tty device name */
  int status;

  slotp = &slots[linenr];

  /* Error channel for between fork and exec. */
  if (pipe(err) < 0) err[0] = err[1] = -1;

  if ((pid = fork()) == -1 ) {
        report(2, "fork()");
        sleep(10);
        return;
  }

  if (pid == 0) {
        /* Child */
        close(err[0]);
        fcntl(err[1], F_SETFD, fcntl(err[1], F_GETFD) | FD_CLOEXEC);

        /* A new session. */
        setsid();

        /* Construct device name. */
        strcpy(line, "/dev/");
        strncat(line, ttyp->ty_name, sizeof(line) - 6);

        /* Open the line for standard input and output. */
        close(0);
        close(1);
        if (open(line, O_RDWR) < 0 || dup(0) < 0) {
                write(err[1], &errno, sizeof(errno));
                _exit(1);
        }

        if (ttyp->ty_init != NULL && ttyp->ty_init[0] != NULL) {
                /* Execute a command to initialize the terminal line. */

                if ((pid = fork()) == -1) {
                        report(2, "fork()");
                        errno= 0;
                        write(err[1], &errno, sizeof(errno));
                        _exit(1);
                }

                if (pid == 0) {
                        alarm(10);
                        execute(ttyp->ty_init);
                        report(2, ttyp->ty_init[0]);
                        _exit(1);
                }

                while (waitpid(pid, &status, 0) != pid) {}
                if (status != 0) {
                        tell(2, "init: ");
                        tell(2, ttyp->ty_name);
                        tell(2, ": ");
                        tell(2, ttyp->ty_init[0]);
                        tell(2, ": bad exit status\n");
                        errno = 0;
                        write(err[1], &errno, sizeof(errno));
                        _exit(1);
                }
        }

        /* Redirect standard error too. */
        dup2(0, 2);

        /* Execute the getty process. */
        execute(ttyp->ty_getty);

        /* Oops, disaster strikes. */
        fcntl(2, F_SETFL, fcntl(2, F_GETFL) | O_NONBLOCK);
        if (linenr != 0) report(2, ttyp->ty_getty[0]);
        write(err[1], &errno, sizeof(errno));
        _exit(1);
  }

  /* Parent */
  if (ttyp != &TT_REBOOT) slotp->pid = pid;

  close(err[1]);
  if (read(err[0], &errno, sizeof(errno)) != 0) {
        /* If an errno value goes down the error pipe: Problems. */

        switch (errno) {
        case ENOENT:
        case ENODEV:
        case ENXIO:
                /* Device nonexistent, no driver, or no minor device. */
                slotp->errct = ERRCT_DISABLE;
                close(err[0]);
                return;
        case 0:
                /* Error already reported. */
                break;
        default:
                /* Any other error on the line. */
                report(2, ttyp->ty_name);
        }
        close(err[0]);

        if (++slotp->errct >= ERRCT_DISABLE) {
                tell(2, "init: ");
                tell(2, ttyp->ty_name);
                tell(2, ": excessive errors, shutting down\n");
        } else {
                sleep(5);
        }
        return;
  }
  close(err[0]);

  if (ttyp != &TT_REBOOT) wtmp(LOGIN_PROCESS, linenr, ttyp->ty_name, pid);
  slotp->errct = 0;
}

int execute(char **cmd)
{
  /* Execute a command with a path search along /sbin:/bin:/usr/sbin:/usr/bin.
   */
  static char *nullenv[] = { NULL };
  char command[128];
  char *path[] = { "/sbin", "/bin", "/usr/sbin", "/usr/bin" };
  int i;

  if (cmd[0][0] == '/') {
        /* A full path. */
        return execve(cmd[0], cmd, nullenv);
  }

  /* Path search. */
  for (i = 0; i < 4; i++) {
        if (strlen(path[i]) + 1 + strlen(cmd[0]) + 1 > sizeof(command)) {
                errno= ENAMETOOLONG;
                return -1;
        }
        strcpy(command, path[i]);
        strcat(command, "/");
        strcat(command, cmd[0]);
        execve(command, cmd, nullenv);
        if (errno != ENOENT) break;
  }
  return -1;
}

void wtmp(type, linenr, line, pid)
int type;                       /* type of entry */
int linenr;                     /* line number in ttytab */
char *line;                     /* tty name (only good on login) */
pid_t pid;                      /* pid of process */
{
/* Log an event into the UTMP and WTMP files. */

  struct utmp utmp;             /* UTMP/WTMP User Accounting */
  int fd;

  /* Clear the utmp record. */
  memset((void *) &utmp, 0, sizeof(utmp));

  /* Fill in utmp. */
  switch (type) {
  case BOOT_TIME:
        /* Make a special reboot record. */
        strcpy(utmp.ut_name, "reboot");
        strcpy(utmp.ut_line, "~");
        break;

  case LOGIN_PROCESS:
        /* A new login, fill in line name. */
        strncpy(utmp.ut_line, line, sizeof(utmp.ut_line));
        break;

  case DEAD_PROCESS:
        /* A logout.  Use the current utmp entry, but make sure it is a
         * user process exiting, and not getty or login giving up.
         */
        if ((fd = open(PATH_UTMP, O_RDONLY)) < 0) {
                if (errno != ENOENT) report(2, PATH_UTMP);
                return;
        }
        if (lseek(fd, (off_t) (linenr+1) * sizeof(utmp), SEEK_SET) == -1
                || read(fd, &utmp, sizeof(utmp)) == -1
        ) {
                report(2, PATH_UTMP);
                close(fd);
                return;
        }
        close(fd);
        if (utmp.ut_type != USER_PROCESS) return;
        strncpy(utmp.ut_name, "", sizeof(utmp.ut_name));
        break;
  }

  /* Finish new utmp entry. */
  utmp.ut_pid = pid;
  utmp.ut_type = type;
  utmp.ut_time = time((time_t *) 0);

  switch (type) {
  case LOGIN_PROCESS:
  case DEAD_PROCESS:
        /* Write new entry to utmp. */
        if ((fd = open(PATH_UTMP, O_WRONLY)) < 0
                || lseek(fd, (off_t) (linenr+1) * sizeof(utmp), SEEK_SET) == -1
                || write(fd, &utmp, sizeof(utmp)) == -1
        ) {
                if (errno != ENOENT) report(2, PATH_UTMP);
        }
        if (fd != -1) close(fd);
        break;
  }

  switch (type) {
  case BOOT_TIME:
  case DEAD_PROCESS:
        /* Add new wtmp entry. */
        if ((fd = open(PATH_WTMP, O_WRONLY | O_APPEND)) < 0
                  || write(fd, &utmp, sizeof(utmp)) == -1
        ) {
                if (errno != ENOENT) report(2, PATH_WTMP);
        }
        if (fd != -1) close(fd);
        break;
  }
}

void tell(fd, s)
int fd;
char *s;
{
        write(fd, s, strlen(s));
}

void report(fd, label)
int fd;
char *label;
{
        int err = errno;

        tell(fd, "init: ");
        tell(fd, label);
        tell(fd, ": ");
        tell(fd, strerror(err));
        tell(fd, "\n");
        errno= err;
}

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