pty/pty_fork.c

This is pty/pty_fork.c (Listing 64-2, page 1386), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

 

Download pty/pty_fork.c

  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* pty_fork.c

   Implements ptyFork(), a function that creates a child process connected to
   the parent (i.e., the calling process) via a pseudoterminal (pty). The child
   is placed in a new session, with the pty slave as its controlling terminal,
   and its standard input, output, and error connected to the pty slave.

   In the parent, 'masterFd' is used to return the file descriptor for the
   pty master.

   If 'slaveName' is non-NULL, then it is used to return the name of the pty
   slave. If 'slaveName' is not NULL,  then 'snLen' should be set to indicate
   the size of the buffer pointed to by 'slaveName'.

   If 'slaveTermios' and 'slaveWS' are non-NULL, then they are used respectively
   to set the terminal attributes and window size of the pty slave.

   Returns:
        in child: 0
        in parent: PID of child or -1 on error
*/
#include <fcntl.h>
#include <termios.h>
#include <sys/ioctl.h>
#include "pty_master_open.h"
#include "pty_fork.h"                   /* Declares ptyFork() */
#include "tlpi_hdr.h"

#define MAX_SNAME 1000                  /* Maximum size for pty slave name */
pid_t
ptyFork(int *masterFd, char *slaveName, size_t snLen,
        const struct termios *slaveTermios, const struct winsize *slaveWS)
{
    int mfd, slaveFd, savedErrno;
    pid_t childPid;
    char slname[MAX_SNAME];

    mfd = ptyMasterOpen(slname, MAX_SNAME);
    if (mfd == -1)
        return -1;

    if (slaveName != NULL) {            /* Return slave name to caller */
        if (strlen(slname) < snLen) {
            strncpy(slaveName, slname, snLen);

        } else {                        /* 'slaveName' was too small */
            close(mfd);
            errno = EOVERFLOW;
            return -1;
        }
    }

    childPid = fork();

    if (childPid == -1) {               /* fork() failed */
        savedErrno = errno;             /* close() might change 'errno' */
        close(mfd);                     /* Don't leak file descriptors */
        errno = savedErrno;
        return -1;
    }

    if (childPid != 0) {                /* Parent */
        *masterFd = mfd;                /* Only parent gets master fd */
        return childPid;                /* Like parent of fork() */
    }

    /* Child falls through to here */

    if (setsid() == -1)                 /* Start a new session */
        err_exit("ptyFork:setsid");

    close(mfd);                         /* Not needed in child */

    slaveFd = open(slname, O_RDWR);     /* Becomes controlling tty */
    if (slaveFd == -1)
        err_exit("ptyFork:open-slave");

#ifdef TIOCSCTTY                        /* Acquire controlling tty on BSD */
    if (ioctl(slaveFd, TIOCSCTTY, 0) == -1)
        err_exit("ptyFork:ioctl-TIOCSCTTY");
#endif

    if (slaveTermios != NULL)           /* Set slave tty attributes */
        if (tcsetattr(slaveFd, TCSANOW, slaveTermios) == -1)
            err_exit("ptyFork:tcsetattr");

    if (slaveWS != NULL)                /* Set slave tty window size */
        if (ioctl(slaveFd, TIOCSWINSZ, slaveWS) == -1)
            err_exit("ptyFork:ioctl-TIOCSWINSZ");

    /* Duplicate pty slave to be child's stdin, stdout, and stderr */

    if (dup2(slaveFd, STDIN_FILENO) != STDIN_FILENO)
        err_exit("ptyFork:dup2-STDIN_FILENO");
    if (dup2(slaveFd, STDOUT_FILENO) != STDOUT_FILENO)
        err_exit("ptyFork:dup2-STDOUT_FILENO");
    if (dup2(slaveFd, STDERR_FILENO) != STDERR_FILENO)
        err_exit("ptyFork:dup2-STDERR_FILENO");

    if (slaveFd > STDERR_FILENO)        /* Safety check */
        close(slaveFd);                 /* No longer need this fd */

    return 0;                           /* Like child of fork() */
}

 

Download pty/pty_fork.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

Valid XHTML 1.1