busybox init and rcS

[Rob Landley]

On Monday 09 January 2006 07:39, hinko.kocevar at cetrtapot.si wrote:
> Rob Landley wrote:
> > Well, first off, could you try a current snapshot so we know we're
> > working with fresh up-to-the-minute bugs?  (We're a couple days away from
> > a new release.)
> >
> > Rob
>
> I've did a bit of debugging and found out following. If I modify the
> function waitfor() in init.c like this (see waitpid line and the one
> following it) rcS is started and returns, also shell prompt is shown.
> Without WNOHANG flag for waitpid() and additional message to print on
> CONSOLE it does not work.

Uh-huh.  Telling waitpid() to return immediately and _spinning_ on it is a 
workaround for something broken, not a fix.

> static int waitfor(const struct init_action *a)
> {
>      int pid;
>      int status, wpid;
>
>      pid = run(a);
>      while (1) {
>          wpid = waitpid(pid,&status,WNOHANG);
>          message(CONSOLE, "po waitpid wpid = %d", wpid);
>
>          if (wpid == pid) {
>              break;
>          }
>          if (wpid == -1 && errno == ECHILD) {
>              /* we missed its termination */
>              break;
>          }
>          /* FIXME other errors should maybe trigger an error, but allow
>           * the program to continue */
>      }
>      return wpid;
> }
>
> In console I get this output (enabled bit of debugging here):
> ....
> command='/etc/init.d/rcS' action='1' terminal='/dev/ttyS0'
> command='-/bin/sh' action='4' terminal='/dev/ttyS0'
> command='/sbin/init' action='128' terminal='/dev/ttyS0'
> command='/sbin/reboot' action='32' terminal='/dev/ttyS0'
> command='/bin/umount -a -r' action='64' terminal='/dev/ttyS0'
> command='/sbin/swapoff -a' action='64' terminal='/dev/ttyS0'
>
> Starting pid 654, console /dev/ttyS0: '/etc/init.d/rcS'
> po waitpid wpid = 0
> po waitpid wpid = 0
> po waitpid wpid = 0
> po waitpid wpid = 0
>
> ... A LOT OF LINES ...

Well you're spinning instead of waiting.

> po waitpid wpid = 0
> po waitpid wpid = 0
> po waitpid wpid = 0
> po waitpid wpid = 0
> po waitpid wpid = 653

If that's really making a difference, something is wrong with either your 
kernel or your C library.  It sounds like sigchld is never being delivered.  
(You're waiting on a specific pid, so I think it's actually polling that 
process's state and will happily do the zombie cleanup even if it ever 
actually received a signal.)

How much of a workout have you given the kernel you're running on the axis 
etrax?  Do you know if signal delivery on the sucker actually works?

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.