Ich weis schon, warum man fork()/setsid()/fork() in einem daemon macht. Wir sind hier aber in pid1. sysvinit. Deshalb frag ich. Wenn ich allen Subprozessen die Möglichkeit nehme ein Terminal zu bekommen, kann ein weiterer Subprozess ja auch kein Terminal mehr bekommen. Wie bekommt dann bsp. ein getty ein Controlling terminal?
Code: Alles auswählen
/*
* Fork and execute.
*
* This function is too long and indents too deep.
*
*/
static
pid_t spawn(CHILD *ch, int *res)
{
char *args[16]; /* Argv array */
char buf[136]; /* Line buffer */
int f, st; /* Scratch variables */
char *ptr; /* Ditto */
time_t t; /* System time */
int oldAlarm; /* Previous alarm value */
char *proc = ch->process; /* Command line */
pid_t pid, pgrp; /* child, console process group. */
sigset_t nmask, omask; /* For blocking SIGCHLD */
struct sigaction sa;
*res = -1;
buf[sizeof(buf) - 1] = 0;
/* Skip '+' if it's there */
if (proc[0] == '+') proc++;
ch->flags |= XECUTED;
if (ch->action == RESPAWN || ch->action == ONDEMAND) {
/* Is the date stamp from less than 2 minutes ago? */
time(&t);
if (ch->tm + TESTTIME > t) {
ch->count++;
} else {
ch->count = 0;
ch->tm = t;
}
/* Do we try to respawn too fast? */
if (ch->count >= MAXSPAWN) {
initlog(L_VB,
"Id \"%s\" respawning too fast: disabled for %d minutes",
ch->id, SLEEPTIME / 60);
ch->flags &= ~RUNNING;
ch->flags |= FAILING;
/* Remember the time we stopped */
ch->tm = t;
/* Try again in 5 minutes */
oldAlarm = alarm(0);
if (oldAlarm > SLEEPTIME || oldAlarm <= 0) oldAlarm = SLEEPTIME;
alarm(oldAlarm);
return(-1);
}
}
/* See if there is an "initscript" (except in single user mode). */
if (access(INITSCRIPT, R_OK) == 0 && runlevel != 'S') {
/* Build command line using "initscript" */
args[1] = SHELL;
args[2] = INITSCRIPT;
args[3] = ch->id;
args[4] = ch->rlevel;
args[5] = "unknown";
for(f = 0; actions[f].name; f++) {
if (ch->action == actions[f].act) {
args[5] = actions[f].name;
break;
}
}
args[6] = proc;
args[7] = NULL;
} else if (strpbrk(proc, "~`!$^&*()=|\\{}[];\"'<>?")) {
/* See if we need to fire off a shell for this command */
/* Give command line to shell */
args[1] = SHELL;
args[2] = "-c";
strcpy(buf, "exec ");
strncat(buf, proc, sizeof(buf) - strlen(buf) - 1);
args[3] = buf;
args[4] = NULL;
} else {
/* Split up command line arguments */
buf[0] = 0;
strncat(buf, proc, sizeof(buf) - 1);
ptr = buf;
for(f = 1; f < 15; f++) {
/* Skip white space */
while(*ptr == ' ' || *ptr == '\t') ptr++;
args[f] = ptr;
/* May be trailing space.. */
if (*ptr == 0) break;
/* Skip this `word' */
while(*ptr && *ptr != ' ' && *ptr != '\t' && *ptr != '#')
ptr++;
/* If end-of-line, break */
if (*ptr == '#' || *ptr == 0) {
f++;
*ptr = 0;
break;
}
/* End word with \0 and continue */
*ptr++ = 0;
}
args[f] = NULL;
}
args[0] = args[1];
while(1) {
/*
* Block sigchild while forking.
*/
sigemptyset(&nmask);
sigaddset(&nmask, SIGCHLD);
sigprocmask(SIG_BLOCK, &nmask, &omask);
if ((pid = fork()) == 0) {
close(0);
close(1);
close(2);
if (pipe_fd >= 0) close(pipe_fd);
sigprocmask(SIG_SETMASK, &omask, NULL);
/*
* In sysinit, boot, bootwait or single user mode:
* for any wait-type subprocess we _force_ the console
* to be its controlling tty.
*/
if (strchr("*#sS", runlevel) && ch->flags & WAITING) {
/*
* We fork once extra. This is so that we can
* wait and change the process group and session
* of the console after exit of the leader.
*/
setsid();
if ((f = console_open(O_RDWR|O_NOCTTY)) >= 0) {
/* Take over controlling tty by force */
(void)ioctl(f, TIOCSCTTY, 1);
dup(f);
dup(f);
}
/*
* 4 Sep 2001, Andrea Arcangeli:
* Fix a race in spawn() that is used to deadlock init in a
* waitpid() loop: must set the childhandler as default before forking
* off the child or the chld_handler could run before the waitpid loop
* has a chance to find its zombie-child.
*/
SETSIG(sa, SIGCHLD, SIG_DFL, SA_RESTART);
if ((pid = fork()) < 0) {
initlog(L_VB, "cannot fork: %s",
strerror(errno));
exit(1);
}
if (pid > 0) {
pid_t rc;
/*
* Ignore keyboard signals etc.
* Then wait for child to exit.
*/
SETSIG(sa, SIGINT, SIG_IGN, SA_RESTART);
SETSIG(sa, SIGTSTP, SIG_IGN, SA_RESTART);
SETSIG(sa, SIGQUIT, SIG_IGN, SA_RESTART);
while ((rc = waitpid(pid, &st, 0)) != pid) // <<< warum hier ein waitpid?
if (rc < 0 && errno == ECHILD)
break;
/*
* Small optimization. See if stealing
* controlling tty back is needed.
*/
pgrp = tcgetpgrp(f);
if (pgrp != getpid())
exit(0);
/*
* Steal controlling tty away. We do
* this with a temporary process.
*/
if ((pid = fork()) < 0) {
initlog(L_VB, "cannot fork: %s",
strerror(errno));
exit(1);
}
if (pid == 0) {
setsid();
(void)ioctl(f, TIOCSCTTY, 1);
exit(0);
}
while((rc = waitpid(pid, &st, 0)) != pid)
if (rc < 0 && errno == ECHILD)
break;
exit(0);
}
/* Set ioctl settings to default ones */
console_stty();
} else {
setsid();
if ((f = console_open(O_RDWR|O_NOCTTY)) < 0) {
initlog(L_VB, "open(%s): %s", console_dev,
strerror(errno));
f = open("/dev/null", O_RDWR);
}
dup(f);
dup(f);
}
/*
* Update utmp/wtmp file prior to starting
* any child. This MUST be done right here in
* the child process in order to prevent a race
* condition that occurs when the child
* process' time slice executes before the
* parent (can and does happen in a uniprocessor
* environment). If the child is a getty and
* the race condition happens, then init's utmp
* update will happen AFTER the getty runs
* and expects utmp to be updated already!
*
* Do NOT log if process field starts with '+'
* FIXME: that's for compatibility with *very*
* old getties - probably it can be taken out.
*/
if (ch->process[0] != '+')
write_utmp_wtmp("", ch->id, getpid(), INIT_PROCESS, "");
/* Reset all the signals, set up environment */
for(f = 1; f < NSIG; f++) SETSIG(sa, f, SIG_DFL, SA_RESTART);
environ = init_buildenv(1);
/*
* Execute prog. In case of ENOEXEC try again
* as a shell script.
*/
execvp(args[1], args + 1);
if (errno == ENOEXEC) {
args[1] = SHELL;
args[2] = "-c";
strcpy(buf, "exec ");
strncat(buf, proc, sizeof(buf) - strlen(buf) - 1);
args[3] = buf;
args[4] = NULL;
execvp(args[1], args + 1);
}
initlog(L_VB, "cannot execute \"%s\"", args[1]);
if (ch->process[0] != '+')
write_utmp_wtmp("", ch->id, getpid(), DEAD_PROCESS, NULL);
exit(1);
}
*res = pid;
sigprocmask(SIG_SETMASK, &omask, NULL);
INITDBG(L_VB, "Started id %s (pid %d)", ch->id, pid);
if (pid == -1) {
initlog(L_VB, "cannot fork, retry..");
do_sleep(5);
continue;
}
return(pid);
}
}
/*
* Start a child running!
*/
static
void startup(CHILD *ch)
{
/*
* See if it's disabled
*/
if (ch->flags & FAILING) return;
switch(ch->action) {
case SYSINIT:
case BOOTWAIT:
case WAIT:
case POWERWAIT:
case POWERFAILNOW:
case POWEROKWAIT:
case CTRLALTDEL:
if (!(ch->flags & XECUTED)) ch->flags |= WAITING;
case KBREQUEST:
case BOOT:
case POWERFAIL:
case ONCE:
if (ch->flags & XECUTED) break;
case ONDEMAND:
case RESPAWN:
ch->flags |= RUNNING;
(void)spawn(ch, &(ch->pid));
break;
}
}
Es kann auch einfach sein, das hier mehr Nutzer als Programmierer da sind