On Thu, Dec 22, 2005 at 09:37:02AM +1300, Paul M wrote:
> You need to fork off a new process then exec the tool from the child.
> The child process does not return. You can open pipes prior to the
> fork, since the parent and child process share file descriptors.
>
> Something like this:
>
> int socks[2];
>
> /* open socket pair */
> int retval = pipe(socks);
> if (retval < 0)
> perror("opening socket pair");
>
> /* fork off a child process */
> pid_t pid = fork();
> if (pid == -1)
> perror("Failed to fork\n");
>
> if (pid == 0) {
> /* child process */
> close(socks[1]);
> dup2(socks[1], 2);
dup2(socks[1], 1);
close(socks[1]);
But he wants two way communication, so he will have to create to pipes
or use socketpair:
void childreap(int s) {
while (waitpid(0, NULL, WNOHANG) > 0);
}
creatproc() {
int p[4];
pipe(p);
pipe(p+2);
switch (fork()) {
case -1:
/* error */
...
case 0:
/* child */
dup2(p[0], STDIN_FILENO);
dup2(p[3], STDOUT_FILENO);
close(p[0]);
close(p[1]);
close(p[2]);
close(p[3]);
execl(program, program, arg1, arg2, ..., NULL);
perror(program);
exit(1);
default:
close(p[0]);
close(p[3]);
into_proc = p[1];
from_proc = p[2];
signal(SIGPIPE, SIG_IGN);
signal(SIGCHLD, childreap);
}
with socketpair:
creatproc() {
int p[2];
socketpair(PF_UNIX, SOCK_STREAM, p);
switch (fork()) {
case -1:
/* error */
...
case 0:
/* child */
dup2(p[0], STDIN_FILENO);
dup2(p[0], STDOUT_FILENO);
close(p[0]);
close(p[1]);
execl(program, program, arg1, arg2, ..., NULL);
perror(program);
exit(1);
default:
close(p[0]);
from_into_proc = p[1];
signal(SIGPIPE, SIG_IGN);
signal(SIGCHLD, childreap);
}
Care must be given to prevent deadlocks (trying to write to the process
while it's trying to read from stdin and vice-versa).
Either use poll or select.
--
lfr
0/0
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