I need to write a Linuxland daemon that talks to our custom hardware. I
would like to use the /init process to start, and if necessary, restart it.
I have made this entry into the init.<hardware>.rc file that looks like
this:
service rsgd /system/bin/rsgd
class main
user system
Here is my daemon (just a skeleton now, but it runs):
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
#define DAEMONIZE
int main(void)
{
#ifdef DAEMONIZE
pid_t pid, sid;
/* Fork off the parent process */
pid = fork();
if (pid < 0) {
exit(EXIT_FAILURE);
}
/* Exit the parent process. */
if (pid > 0) {
exit(EXIT_SUCCESS);
}
#endif
/* Change the file mode mask */
umask(0);
#ifdef DAEMONIZE
/* Create a new SID for the child process */
sid = setsid();
if (sid < 0) {
/* Log the failure */
exit(EXIT_FAILURE);
}
#endif
/* Change the current working directory */
if ((chdir("/")) < 0) {
/* Log the failure */
exit(EXIT_FAILURE);
}
/* Close out the standard file descriptors */
close(STDIN_FILENO);
close(STDOUT_FILENO);
close(STDERR_FILENO);
/* Daemon-specific initialization goes here */
/* The Big Loop */
while (1) {
/* Do some task here ... */
usleep(100000); /* wait 100 milliseconds */
}
exit(EXIT_SUCCESS);
}
Nothing fancy. When I build the system, the daemon gets created properly,
and lives in /system/bin, as expected. When I boot the system, however,
/init continually starts my daemon, many times, until the system eventually
runs out of memory!
Is there something my daemon needs to do so /init doesn't think it has died
and needs to restart?
Well, as I wrote this originally, I had an "Aha!" moment - /init must be
acting on the exit of the parent process! That would explain why it starts
another instance, even though the prior one is still around. So I got rid
of the code with the DAEMONIZE conditionals, but that just hangs the system
immediately after print this message:
Freeing init memory: 248K
So, what is the proper way to write a Linux daemon that /init can manage
for me? Any ideas welcome!
Thanks!
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