pty/pty_master_open_bsd.c

/* pty_master_open_bsd.c

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

   Note: BSD pseudoterminals are not specified in SUSv3, and are considered
   obsolete on Linux.

   See also pty_master_open.c.
*/
#include <fcntl.h>
#include "pty_master_open.h"            /* Declares ptyMasterOpen() */
#include "tlpi_hdr.h"

#define PTYM_PREFIX     "/dev/pty"
#define PTYS_PREFIX     "/dev/tty"
#define PTY_PREFIX_LEN  (sizeof(PTYM_PREFIX) - 1)
#define PTY_NAME_LEN    (PTY_PREFIX_LEN + sizeof("XY"))
#define X_RANGE         "pqrstuvwxyzabcde"
#define Y_RANGE         "0123456789abcdef"

/* Open a BSD 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, n;
    char *x, *y;
    char masterName[PTY_NAME_LEN];

    if (PTY_NAME_LEN > snLen) {
        errno = EOVERFLOW;
        return -1;
    }

    memset(masterName, 0, PTY_NAME_LEN);
    strncpy(masterName, PTYM_PREFIX, PTY_PREFIX_LEN);

    /* Scan through all possible BSD pseudoterminal master names until
       we find one that we can open. */

    for (x = X_RANGE; *x != '\0'; x++) {
        masterName[PTY_PREFIX_LEN] = *x;

        for (y = Y_RANGE; *y != '\0'; y++) {
            masterName[PTY_PREFIX_LEN + 1] = *y;

            masterFd = open(masterName, O_RDWR);

            if (masterFd == -1) {
                if (errno == ENOENT)    /* No such file */
                    return -1;          /* Probably no more pty devices */
                else                    /* Other error (e.g., pty busy) */
                    continue;

            } else {            /* Return slave name corresponding to master */
                n = snprintf(slaveName, snLen, "%s%c%c", PTYS_PREFIX, *x, *y);
                if (n >= snLen) {
                    errno = EOVERFLOW;
                    return -1;
                } else if (n == -1) {
                    return -1;
                }

                return masterFd;
            }
        }
    }

    return -1;                  /* Tried all ptys without success */
}