Hallo,
 Am using pipes in my C code to talk to a child process that I have
forked. However, I keep on getting an certain erro messge that I cannot
understand. My error is as below
================================================================
<Can't set terminal configuration (fd #0)>
<TCSETA>: I/O error
================================================================

could anyone help me in diagnosing the problem and possibly suggest a
suitable solution.

I have attached my code below
===================================================================
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main(void)
{
        int result1, result2;
        int     parentfd[2],childfd[2],nbytes;
        pid_t   childpid;
        char    string[] = "Connecting..........!\n";
        char    string2[] = "Am Connected!\n";
        char    readbuffer[80];

        pipe(parentfd);
        pipe(childfd);

        if((childpid = fork()) == -1)
        {
                perror("fork");
                exit(1);
        }

        if(childpid == 0)
        {
                /* Child process closes up output side of pipe */
                close(parentfd[1]);
                close(childfd[0]);
                /* Read in a string from the pipe */
                nbytes = read(parentfd[0], readbuffer,
sizeof(readbuffer));
                printf("\nChild Received string: %s", readbuffer);
                /* Send "string" through the output side of pipe */
                write(childfd[1], string2, (strlen(string)+1));

                result1 = dup(parentfd[0]);
                printf("\nValue returned by dup %d",result1);
                printf("\nInvoking a process");
                result1 = execlp("/usr/sbin/padem", "0302" , NULL);
                printf("\nValue returned by execlp() %d",result1);

                exit(0);
        }
        else
        {
                /* Parent process closes up input side of pipe */
                close(parentfd[0]);
                close(childfd[1]);
                /* Send "string" through the output side of pipe */
                write(parentfd[1], string, (strlen(string)+1));
                /* Read in a string from the pipe */
                nbytes = read(childfd[0], readbuffer,
sizeof(readbuffer));
                printf("\nParent Received string: %s", readbuffer);



        }

        return(0);
}

===================================================================

I don't think it's a problem with your pipes as such.. what is this
`padem` program and can you verify if you get the same error even when
you don't call `padem`. I tried your code in linux, freebsd and tru64,
I didn't get any errors. 

vishal

Thanks for your response.

padem is a PAD EMULATOR in my hp-ux system that allows me to telnet to
a remote system..
So am trying to actual create a session with this emulator called
padem. Something similar like creating a telnet session in a C program.

>  <Can't set terminal configuration (fd #0)>

I think that your "padem" program is unhappy because its stdin/stdout
are not connected to a terminal, but instead to a pipe.  I suggest
running strace -f and looking at what padem does immeidately before the
error.  I bet that it is doing an ioctl() or something similar that is
not supported on the pipe.

If this is true, you might consider using forkpty() instead of pipe()
and fork().

--Phil.

Enos Meroka wrote:
> Hallo,
>  Am using pipes in my C code to talk to a child process that I have
> forked. However, I keep on getting an certain erro messge that I cannot
> understand. My error is as below
> ================================================================
> <Can't set terminal configuration (fd #0)>
> <TCSETA>: I/O error
> ================================================================
> 
> could anyone help me in diagnosing the problem and possibly suggest a
> suitable solution.

Hi Enos,

as far as I can see, there is nothing wrong with your code ...
    the error obviously comes from something completely different ...

There are programs in this world (like editors etc.) that wants
    to be connected to something looking and feeling
    like a terminal ... also the program only gets it's stdin/stdout
    connected to this terminal, it can use ioctl() with a termios-
    structure and the parameters TCGETA / TCSETA to get/set
    terminal-settings ...
Obviously the pipes htat you used to connect to your childprogram
    do not support these terminal-speccific ioctl()s ... and that is
    the reason why the forked program is complaining .
    If there is no command-line option to tell the program to
    disregard the fact, that it's not connected to a terminal, then
    you have only one option:
    -> Give your program a terminal!
To do this, you use something different than pipes ... you
    use a thing called a pseudo-tty (yes indeed, this already sounds like
    a terminal) ... the setup of a pseudo-terminal is unfortunately
    a bit more difficult than opening pipes ... If you google for
    pseudo-tty you will quite likely find something helpful.
I'll only give you a very brief descriptnion of what to do:

    Before fork() do the following:
    masterfd=open("/dev/ptmx",RDWR)
         (this is the Master-Side-Multiplexer of the
                           pseudos)
    grantpt(masterfd)
    unlockpt(masterfd)

    now fork()

    in the child do

    ptr = ptsname(masterfd)
          (this gives you the name of the associated slave-side)
    slavefd=open(ptr,RDWR)
    close(masterfd)

    dup2(slavefd,0) dup2(slavefd,1); dup2(slavefd,2)
    close(slavefd)
       (this connects stdin/out/err to the slave-side)
    exec( whatever you want to exec )


    in the master do

    read(masterfd,...) and write(masterfd,...)

    write(master,...) will send data to the program you execed
    read(master,...) will read data that was being sent by the program.

That's it.

Good luck ... Rainer

> a pseudo-terminal is unfortunately
> a bit more difficult than opening pipes

If your library supports forkpty(), it becomes quite simple.  But it is
still a good idea to understand what is going on underneath.

--Phil.

phil_gg04@treefic.com wrote:
>>a pseudo-terminal is unfortunately
>>a bit more difficult than opening pipes
> 
> 
> If your library supports forkpty(), it becomes quite simple.  But it is
> still a good idea to understand what is going on underneath.
> 
> --Phil.
> 

oh come on Phil ...

every "real programmer" has to produce a certain amount
    of _special_ code-modules in his(her) life ...

    -> a doubly-linked list
       (just for the fun of handling this strange
        next->previous=previous->next stuff.)
    -> an implementation of qsort
       (to check if your's i faster than the library implementation)
    -> a clever replacement for malloc()/free() that checks
       if verything is still in order.
       (you simply cannt live without it)
    ...
    and of corse a module handling pseudo-tty's ;-)
       (just for the fun of doing it)

Regards ... Rainer

> oh come on Phil ...
> every "real programmer" has to produce a certain amount
>    of _special_ code-modules in his(her) life ...
>
> -> a clever replacement for malloc()/free() that checks

Strangely enough, just yesterday was was writing my own memory
allocation functions.....

--Phil.