I'm a bit confused. If you tell init to wait then it seems like it ought
to wait. If your application is going to run forever couldn't it fork
itself and have the parent exit. That would free up the init to
continue.
Standard systems use wait to run startup scripts that execute
applications in the background and then exit themselves. Seems like you
could add a small script to fire up your application from a startup
script and have init wait on that. Of course then you might need to
compile in the ash shell, which you may not otherwise want.
Also, seems like you could use "respawn". Seems like respawn allows init
to go on to the next step while the application continues running. If
your application runs forever it will only get run the one time.
It seems wrong to change the way wait works, because there may be people
that use wait that actually want init to wait and not reap children.
Just my opinion.
Chris Kottaridis (chris.kottaridis at windriver.com)
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
On Fri, 2005-07-29 at 10:02 -0500, Jason Schoon wrote:
> We had some issues on our embedded system where init did not always
> reap child processes, resulting in zombies.
>
> This happened because in a production mode we launch our main
> application from a wait line in inittab, and run that forever. This
> caused the init code to never actually reach the loop at the bottom
> that reaps child processes, because it is stopped processing the wait
> command.
>
> This is almost exactly the scenario desribed in this post from a year ago:
> http://www.busybox.net/lists/busybox/2004-August/012420.html
>
> My fix was to enable SIGCHLD handling while in a wait action, and then
> disable it again upon leaving the wait action. The child handler
> simply does a waitpid() without hanging around.
>
> diff -ruN --strip-trailing-cr init-trunk/init.c init/init.c
> --- init-trunk/init.c 2005-07-28 16:07:06.000000000 -0500
> +++ init/init.c 2005-07-28 16:13:52.000000000 -0500
> @@ -185,6 +185,7 @@
>
> /* Function prototypes */
> static void delete_init_action(struct init_action *a);
> +static void child_handler(int sig);
> static int waitfor(const struct init_action *a);
> static void halt_signal(int sig);
>
> @@ -625,6 +626,12 @@
> return pid;
> }
>
> +static void child_handler(int sig)
> +{
> + /* Reap any already available children */
> + (void)waitpid (-1, NULL, WNOHANG);
> +}
> +
> static int waitfor(const struct init_action *a)
> {
> int pid;
> @@ -654,7 +661,11 @@
> tmp = a->next;
> if (a->action == action) {
> if (a->action & (SYSINIT | WAIT | CTRLALTDEL | SHUTDOWN | RESTART)) {
> + if (a->action & WAIT)
> + signal(SIGCHLD, child_handler);
> waitfor(a);
> + if (a->action & WAIT)
> + signal(SIGCHLD, SIG_DFL);
> delete_init_action(a);
> } else if (a->action & ONCE) {
> run(a);
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