tty.c

#ifndef _XOPEN_SOURCE
#define _XOPEN_SOURCE 700
#endif

#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>

#define STATUS_ERROR 127
#define CHECK_NULL(exp) \
    if ((exp) == NULL) { \
        _exit(STATUS_ERROR); \
    }
#define CHECK_ERROR(exp) \
    if ((exp) == -1) { \
        _exit(STATUS_ERROR); \
    }
#define CHECK_ERROR_PRINT(exp) \
    if ((exp) == -1) { \
        dprintf(2, "Error in %s at %s: %s\n", __func__, #exp, strerror(errno)); \
        _exit(STATUS_ERROR); \
    }

pid_t tty_spawn(int fdm, const char *path, char *const argv[], char *const envp[])
    /*
        Spawns a process as a session leader with a pseudo-terminal as
        its controlling terminal, its standard file descriptors
        referring to the terminal, and executing a file with the given
        arguments and environment. The first argument is expected to
        be a file descriptor referring to a master pseudo-terminal
        device as returned by 'posix_openpt'. The next three arguments
        should be given as expected by 'execve'. The process ID of the
        new process is returned, or -1 if one could not be created. If
        the process is created but fails to open the slave device, or
        set up the standard file descriptors, it exits with status 127.
        If it fails to create the session, set the controlling
        terminal or execute the file, it exits with status 127 after
        printing an error message on the terminal that indicates the
        call that failed.
        
        Provided through a library included with the VM to support
        Pharo terminal emulators: it can only be partially replicated
        through the FFI by using 'posix_spawn', as that seems to lack
        a way to set the controlling terminal of the new process.
    */
{
    pid_t pid = fork();
    if (pid == 0)
    {
        char *sname;
        CHECK_NULL(sname = ptsname(fdm));
        int fds;
        CHECK_ERROR(fds = open(sname, O_RDWR));
        CHECK_ERROR(close(fdm));
        CHECK_ERROR(close(0));
        CHECK_ERROR(close(1));
        CHECK_ERROR(close(2));
        CHECK_ERROR(dup(fds));
        CHECK_ERROR(dup(fds));
        CHECK_ERROR(dup(fds));
        CHECK_ERROR(close(fds));
        CHECK_ERROR_PRINT(setsid());
        CHECK_ERROR_PRINT(ioctl(0, TIOCSCTTY, 0));
        CHECK_ERROR_PRINT(execve(path, argv, envp));
    }
    return pid;
}