telnet中的终端操作.

telnet中的终端操作.telnet使用make_new_session来创建一个新的session.在make_new_session中调用xgetpty来创建一个伪终端会话。int FAST_FUNC xgetpty(char *line){    int p;#if ENABLE_FEATURE_DEVPTS    p = open("/dev/ptmx", O_RDWR);    if (p > 0) {        grantpt(p); /* chmod+chown corresponding slave pty */        unlockpt(p); /* (what does this do?) */#if 0 /* if ptsname_r is not available... */        const char *name;        name = ptsname(p); /* find out the name of slave pty */        if (!name) {            bb_perror_msg_and_die("ptsname error (is /dev/pts mounted?)");        }        safe_strncpy(line, name, GETPTY_BUFSIZE);#else        /* find out the name of slave pty */        if (ptsname_r(p, line, GETPTY_BUFSIZE-1) != 0) {            bb_perror_msg_and_die("ptsname error (is /dev/pts mounted?)");        }        line[GETPTY_BUFSIZE-1] = '\0';#endif        return p;    }#else    struct stat stb;    int i;    int j;    strcpy(line, "/dev/ptyXX");    for (i = 0; i         line[8] = "pqrstuvwxyzabcde"[i];        line[9] = '0';        if (stat(line, &stb)             continue;        }        for (j = 0; j             line[9] = j             if (DEBUG)                fprintf(stderr, "Trying to open device: %s\n", line);            p = open(line, O_RDWR | O_NOCTTY);            if (p >= 0) {                line[5] = 't';                return p;            }        }    }#endif /* FEATURE_DEVPTS */    bb_error_msg_and_die("can't find free pty");}好像现在的linux操作系统都是会进入ENABLE_FEATURE_DEVPTS中。即通过打开/dev/ptmx来创建一个伪终端会话。/dev/ptmx是一个用于创建伪终端对。当一个进程调用open打开/dev/ptmx的时候，它会返回主伪终端的fd，并且在会在/dev/pts目录下创建一个对应的slave伪终端。man说明如下。NAME       ptmx and pts - pseudo-terminal master and slaveDESCRIPTION       The  file  /dev/ptmx  is a character file with major number 5 and minor       number 2, usually of mode 0666 and owner.group  of  root.root.   It  is       used to create a pseudo-terminal master and slave pair.       When a process opens /dev/ptmx, it gets a file descriptor for a pseudo-       terminal master (PTM), and a pseudo-terminal slave (PTS) device is cre-       ated in the /dev/pts directory.  Each file descriptor obtained by open-       ing /dev/ptmx is an independent PTM with its own associated PTS,  whose       path can be found by passing the descriptor to ptsname(3).       Before  opening  the  pseudo-terminal slave, you must pass the master’s       file descriptor to grantpt(3) and unlockpt(3).       Once both the pseudo-terminal master and slave are open, the slave pro-       vides  processes  with an interface that is identical to that of a real       terminal.       Data written to the slave is presented  on  the  master  descriptor  as       input.   Data written to the master is presented to the slave as input.       In practice, pseudo-terminals are used for implementing terminal emula-       tors such as xterm(1), in which data read from the pseudo-terminal mas-       ter is interpreted by the application in the same way a  real  terminal       would  interpret  the  data, and for implementing remote-login programs       such as sshd(8), in which data read from the pseudo-terminal master  is       sent across the network to a client program that is connected to a ter-       minal or terminal emulator.       Pseudo-terminals can also be used to send input to programs  that  nor-       mally refuse to read input from pipes (such as su(1), and passwd(1)).FILES       /dev/ptmx, /dev/pts/*NAME       ptsname, ptsname_r - get the name of the slave pseudo-terminalSYNOPSIS       #define _XOPEN_SOURCE       #include        char *ptsname(int fd);       #define _GNU_SOURCE       #include        int ptsname_r(int fd, char *buf, size_t buflen);DESCRIPTION       The ptsname() function returns the name of the slave pseudo-terminal (pty) device corresponding to the master referred to by fd.       The  ptsname_r()  function is the reentrant equivalent of ptsname().  It returns the name of the slave pseudo-terminal device as a null-terminated string       in the buffer pointed to by buf.  The buflen argument specifies the number of bytes available in buf.