Very Computer

Hi,

I am writing a small program that is invoked by inetd.  It is intended
to be a "pass through" server.  It forks/execs another process, which
is normally started by inetd itself.  My "pass through" server will do
some additional logging before the real process is started.

I have the fork/exec working and am able to pass data originating from
the connecting client through my server into the target process.  I
then receive data back from the target process and want to pass it
back to the connecting client.

This part doesn't seem to work - the client hangs even though I have
written the data to stdout in my server code.  I am using select() to
determine when the data from the target process is ready to send back
to the client, and that seems to work, too.

Also, I have my select() call within a while(1) loop.  Under what
condition should I call break in order to exit the loop.  I would like
to know when the child exits so I can exit the parent process.
However, I can't call waitpid while I am processing data between the
client and the target process.

Thanks for any information,
Greg Larkin

Quote:> condition should I call break in order to exit the loop.  I would like
> to know when the child exits so I can exit the parent process.
> However, I can't call waitpid while I am processing data between the
> client and the target process.

You should get SIGCHLD when your child dies/exists/terminates, so setting a
handler for this signal (man sigaction) should give you some clues (though
knowing which of the children has just exited could be a different issue).

Tom

after the target process writes all its data, you call _exit(0); (or
something similar) in it, right? The target process goes zombie.
Normally, you don't really care which child exited. Passing -1 to waitpid()
will clean up any children.
In the parent you catch SIGCHLD like he stated, with the signal handler being
something like the following (note, I use signal() instead of sigaction()..I
haven't learned sigaction() yet)

void zombie_killer(int sig)
{
int status, child_val;
pid_t child_pid=-1;
pid_t get_pid;

/* the argument type. */
while ( (get_pid = waitpid(
        -1,             /* Wait for any child */
        (void *) &status,
        WNOHANG         /* Don't block waiting */
       )) > 0) {
           if (get_pid < 0) break;
           else child_pid = get_pid;
          }

/* No child to clean up, or error */
if (child_pid <= 0) {
        if (child_pid == -1) {
        /* error */
        printf("waitpid() error %d (%s)\n",errno,strerror(errno));
        }
        else if (child_pid == 0) {
        /* no child */
        printf("waitpid() no child to clean up\n");
        }
        /* Reset handler                    */
        signal(SIGCHLD, zombie_killer);
        return;
        }
else {
        printf("waitpid() returned pid %u\n",(unsigned int)child_pid);
        }

/* Reset handler                    */
/* Doing this before the waitpid()  */
/* can lead to an infinite loop     */
signal(SIGCHLD, zombie_killer);

/* Negative child_val indicates some error    */
/* Zero child_val indicates no data available */
    /*
     * We now have the info in 'status' and can manipulate it using
     * the macros in wait.h.
     */
    if (WIFEXITED(status))                /* did child exit normally? */
    {
        child_val = WEXITSTATUS(status); /* get child's exit status */
        printf("Child exited normally with status %d\n",child_val);
    }

Quote:}

-Cygnus
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Anthony J. Biacco                       Network Administrator/Engineer

    "Dream as if you'll live forever, live as if you'll die today"
http://cygnus.ncohafmuta.com                http://www.intergrafix.net
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