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    SubjectRe: forkpty with streams
    On Fri, 2003-07-25 at 15:27, Andries Brouwer wrote:
    > On Thu, Jul 24, 2003 at 11:28:36PM +0000, Andrew Barton wrote:
    > > I've got the 2.4 kernel, and I'm trying to use the forkpty() system call
    > forkpty is not a system call
    > > with the standard I/O stream functions. The calls to forkpty() and
    > > fdopen() and fprintf() all return successfully, but the data never seems
    > > to get to the child process.
    > > pid = forkpty (&fd, 0, 0, 0);
    > > if (pid == 0) {
    > > execlp ("sh", "sh", (void *)0);
    > > } else {
    > > F = fdopen (fd, "w");
    > > fprintf (F, "exit\n");
    > > fflush (F);
    > > wait (0);
    > > }
    > Let me see. Your sh gets input from this pseudotty and sends its
    > output there again. But you never read that filedescriptor.
    > No doubt things will improve if you let the parent read from fd.
    > Andries

    Before I tried using streams, I just used write() to communicate with
    the ptty, but I had the same problem. I found that if I put a read()
    call before and after the write(), it worked. But why? Is this some kind
    of I/O voodoo? How does the reading affect the writing?

    You mentioned that things would improve if I let the parent read from
    fd. Will this work using streams? I have tried opening fd in "r+" mode,
    but in that case I end up reading my own data. Do I need to lay an
    fflush() somewhere inbetween? What is it exactly that causes the data to
    be sent to the parent?

    I appreciate the help.

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