pty/pty_master_open.c

This is pty/pty_master_open.c (Listing 64-1, page 1384), 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.

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/* pty_master_open.c

   Implement our ptyMasterOpen() function, based on UNIX 98 pseudoterminals.
   See comments below.

   See also pty_master_open_bsd.c.
*/
#if ! defined(__sun)
        /* Prevents ptsname() declaration being visible on Solaris 8 */
#if ! defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 600
#define _XOPEN_SOURCE 600
#endif
#endif
#include <stdlib.h>
#include <fcntl.h>
#include "pty_master_open.h"            /* Declares ptyMasterOpen() */
#include "tlpi_hdr.h"

/* Some implementations don't have posix_openpt() */

#if defined(__sun)                      /* Not on Solaris 8 */
#define NO_POSIX_OPENPT
#endif

#ifdef NO_POSIX_OPENPT
static int
posix_openpt(int flags)
{
    return open("/dev/ptmx", flags);
}

#endif
/* Open a pty master, returning file descriptor, or -1 on error.
   On successful completion, the name of the corresponding pty
   slave is returned in 'slaveName'. 'snLen' should be set to
   indicate the size of the buffer pointed to by 'slaveName'. */

int
ptyMasterOpen(char *slaveName, size_t snLen)
{
    int masterFd, savedErrno;
    char *p;

    masterFd = posix_openpt(O_RDWR | O_NOCTTY);         /* Open pty master */
    if (masterFd == -1)
        return -1;

    if (grantpt(masterFd) == -1) {              /* Grant access to slave pty */
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    if (unlockpt(masterFd) == -1) {             /* Unlock slave pty */
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    p = ptsname(masterFd);                      /* Get slave pty name */
    if (p == NULL) {
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    if (strlen(p) < snLen) {
        strncpy(slaveName, p, snLen);
    } else {                    /* Return an error if buffer too small */
        close(masterFd);
        errno = EOVERFLOW;
        return -1;
    }

    return masterFd;
}

 

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