Terminal I/O 

Overview

Terminal I/O has two modes:

1.  Canonical mode input processing.  In this mode, terminal input is processed as lines.  The terminal driver returns at most one line per read request.

2.  Noncanonical mode  input  processing.  The input  characters  ar enot  assembled into lines

If we don’t do anything special, canonical mode is the default.

        We  can think of a terminal device as being controlled by a terminal driver,usually within  the  kernel. Each  terminal device  has  an  input  queue  and  an  output  queue, shown in Figur e18.1.

             All  the  terminal  device  characteristics  that  we  can  examine  and  change  are contained  in  a termios structure. This structure is defined  in  the  header <termios.h>,which we use throughout this chapter:

linux下面找到的termios结构体的定义

struct termios
  {
    tcflag_t c_iflag;           /* input mode flags */
    tcflag_t c_oflag;           /* output mode flags */
    tcflag_t c_cflag;           /* control mode flags */
    tcflag_t c_lflag;           /* local mode flags */
    cc_t c_line;                        /* line discipline */
    cc_t c_cc[NCCS];            /* control characters */
    speed_t c_ispeed;           /* input speed */
    speed_t c_ospeed;           /* output speed */
#define _HAVE_STRUCT_TERMIOS_C_ISPEED 1
#define _HAVE_STRUCT_TERMIOS_C_OSPEED 1
  };


/* c_cc characters */
#define VINTR 0
#define VQUIT 1
#define VERASE 2
#define VKILL 3
#define VEOF 4
#define VTIME 5
#define VMIN 6
#define VSWTC 7
#define VSTART 8
#define VSTOP 9
#define VSUSP 10
#define VEOL 11
#define VREPRINT 12
#define VDISCARD 13
#define VWERASE 14
#define VLNEXT 15
#define VEOL2 16

对于本章理解极其有帮助的图：

Special Input  Characters

#include <stdio.h>
#include <termio.h>
#include <unistd.h>

int main()
{
        struct termios term;
        long vdisable;

        if(isatty(STDIN_FILENO) == 0)
        {
                printf("standard input is not a terminal device\n");
                return 0;
        }

        if((vdisable = fpathconf(STDIN_FILENO,_PC_VDISABLE)) < 0)
        {
                printf("fpathconf error or _POSIX_VDISABLE not in effect\n");
                return 0;
        }

        if(tcgetattr(STDIN_FILENO,&term) < 0)
        {
                printf("tcgetattr error\n");
        }

        term.c_cc[VINTR] = vdisable;
        term.c_cc[VEOF]  = 2;

        if(tcsetattr(STDIN_FILENO,TCSAFLUSH,&term) < 0)
        {
                printf("tcsetattr error\n");
                return 0;
        }

        return 0;
}

Note the following points regarding this program.

?Wemodify  the  terminal  characters  only  if  standardinput  is  a  terminal  device. We  callisatty (Section 18.9) to check this.

?Wefetch the _POSIX_VDISABLEvalue using fpathconf.

?The  functiontcgetattr (Section  18.4)  fetches  a termios structur efro mthe kernel.  After we’ve  modified  this  structure,  we  call tcsetattr to  set  the attributes.  The only attributes that change ar ethe ones we specifically modified.

?Disabling  the  interrupt  key  is  different  from  ignoring  the  interrupt  signal. The program  in  Figure18.10  simply  disables  the  special  character  that  causes  the terminal driver to generate SIGINT.Wecan still use the kill function to send the signal to the process.

Getting and  Setting  Terminal  Attributes

#include <termios.h>
int tcgetattr(int fd ,struct termios *termptr);
int tcsetattr(int fd ,int opt,const struct termios *termptr);
Both return: 0 if OK, ?1 on error

        The  argument opt for tcsetattr lets  us  specify  when  we  want  the  new  terminal attributes to take effect. This argument is specified as one of the following constants.

TCSANOW           The change occurs immediately.

TCSADRAIN         The change occurs after all output has been transmitted. This options hould be used if we                                   are changing the output parameters.

TCSAFLUSH         The  change  occurs  after  all  output  has  been  transmitted.

       The  return  status  of tcsetattr can  be  confusing  to  use  correctly.This  function returns  OK  if  it  was  able  to perform any of  the  requested  actions,  even  if  it  couldn’t perform all the requested actions. If the function returns OK, it is our responsibility to see  whether  all  the  requested  actions  were performed.  This means  that  after  we call tcsetattr to set the desired attributes, we need to call tcgetattr and compare the actual terminal’s attributes to the desired attributes to detect any differences.

Terminal  Option  Flags

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

int main()
{
        struct termios term;

        if(tcgetattr(STDIN_FILENO,&term) < 0)
        {
                printf("tcgetattr error\n");
        }

        switch(term.c_cflag & CSIZE)
        {
                case CS5 :
                printf("5 bits/byte\n");
                break;

                case CS6:
                printf("6 bits/byte\n");
                break;

                case CS7 :
                printf("7 bits/byte\n");
                break;


                case CS8 :
                printf("8 bits/byte\n");
                break;

                default :
                        printf("unknown bits/byte\n");
        }

        term.c_cflag &= ~CSIZE;
        term.c_cflag |= CS8;

        if(tcsetattr(STDIN_FILENO,TCSANOW,&term) < 0)
        {
                printf("tcsetattr error\n");
        }

        return 0;
}

flag optiont 太多了, 几乎可以和前面的signal有得一拼了。。。。不一一给出，忘记了就看书吧。。。

stty Command

jasonleaster@ubuntu:/usr/include/x86_64-linux-gnu/bits$ stty -a
speed 38400 baud; rows 41; columns 144; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = M-^?; eol2 = M-^?; swtch = M-^?; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread -clocal -crtscts
-ignbrk brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc ixany imaxbel iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke

NAME
       stty - change and print terminal line settings


SYNOPSIS
       stty [-F DEVICE | --file=DEVICE] [SETTING]...
       stty [-F DEVICE | --file=DEVICE] [-a|--all]
       stty [-F DEVICE | --file=DEVICE] [-g|--save]


DESCRIPTION
       Print or change terminal characteristics.


       -a, --all
              print all current settings in human-readable form


       -g, --save
              print all current settings in a stty-readable form

Baud Rate  Functions

        The  term baud  rate is  a  historical  term  that  should  be  referred  to  today  as  ‘‘bits  per second.’ ’Although  most  terminal  devices  use  the  same  baud  rate  for  both  input  and output,  the  capability  exists  to  set  the  two  rates  to  different  values,  if  the  hardware allows this.

#include <termios.h>
speed_t cfgetispeed(const struct termios *termptr);
speed_t cfgetospeed(const struct termios *termptr);
Both return: baud rate value
int cfsetispeed(struct termios *termptr,speed_t speed);
int cfsetospeed(struct termios *termptr,speed_t speed);
Both return: 0 if OK, ?1 on error

我写这个笔记blog的目的一个是学了留点东西，方便自己查阅自己觉得重点的知识点，第二就是尽量。。。补全author 没有给出的demo

demo：

#include <stdio.h>
#include <unistd.h>
#include <termios.h>

int main()
{
        struct termios term;
        speed_t speed;

        if(isatty(STDIN_FILENO) < 0)
        {
                printf("STDIN_FILENO is not a tty\n");
                return 0;
        }

        if(tcgetattr(STDIN_FILENO,&term) < 0)
        {
                printf("tcgetattr error\n");
        }

        if((speed = cfgetispeed(&term)) < 0)
        {
                printf("cfgetispeed error\n");
        }

        printf("The input baud rate : %d\n",speed);

        if((speed = cfgetospeed(&term)) < 0)
        {
                printf("cfgetispeed error\n");
        }

        printf("The output baud rate : %d\n",speed);

        return 0;
}

Line Control  Functions

#include <termios.h>
int tcdrain(int fd );
int tcflow(int fd ,int action );
int tcflush(intfd ,int queue);
int tcsendbreak(int fd ,int duration);
All four return: 0 if OK,?1 on error

TCOOFF  Output is suspended.

TCOON    Output that was previously suspended is restarted.

TCIOFF    The system transmits a STOP character,which should cause the terminal device to stop sending                        data.

TCION      The system transmits a STAR Tcharacter,which should cause the terminal device to resume sending                  data.

          The tcflush function lets us flush (throw away) either the input buffer (data that has been received by the terminal driver,which we have not read) or the output buffer (data  that  we  have  written,  which  has  not  yet  been transmitted). The queue argument must be one of the following three constants:

TCIFLUSH    The input queue is flushed.

TCOFLUSH  The output queue is flushed.

TCIOFLUSH  Both the input and the output queues ar eflushed

Terminal Identification

#include <stdio.h>
char *ctermid(char *ptr);
Returns: pointer to name of controlling terminal on success, pointer to empty string on error

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

int main()
{
        char name[4096];

        printf("The return string of ctermid when parameter is name:%s\n",ctermid(name));

        printf("The return string of ctermid when parameter is NULL:%s\n",ctermid(NULL));

        return 0;
}

#include <unistd.h>
int isatty(int fd );
Returns: 1 (true) if terminal device, 0 (false) otherwise
char *ttyname(int fd );
Returns: pointer to pathname of terminal,NULL on error

#include <stdio.h>
#include <unistd.h>

int main()
{
        printf("fd 0:%s\n",isatty(0) ? "tty" :"not a tty");

        printf("fd 1:%s\n",isatty(1) ? "tty" :"not a tty");

        printf("fd 2:%s\n",isatty(2) ? "tty" :"not a tty");

        return 0;
}

下面是ttyname 函数实现，写的非常的好，用了两个多小时调试才看明白。。。

#include <stdio.h>
#include <sys/stat.h>
#include <dirent.h>
#include <limits.h>
#include <string.h>
//#include <termios.h>
#include <stdlib.h>

struct devdir
{
        struct devdir *d_next;
        char          *d_name;
};

static struct devdir    *head;
static struct devdir    *tail;

static char             pathname[_POSIX_PATH_MAX + 1];

char* tyy(int fd);

static char* searchdir(char* dirname,struct stat* fdstatp);

static void add(char * dirname);

static void cleanup(void);

static char* searchdir(char* dirname,struct stat* fdstatp);

static void add(char * dirname)
{
        struct devdir   *ddp;
        int             len;

        len = strlen(dirname);

        if((dirname[len - 1] == ‘.‘ && (dirname[len-2] == ‘/‘ || (dirname[len - 2] == ‘.‘ && dirname[len - 3] == ‘/‘))))
        {
                return;
        }
        if(strcmp(dirname,"/dev/fd") == 0)
        {
                return;
        }

        ddp = malloc(sizeof(struct devdir));

        if(ddp == NULL)
        {
                return;
        }

        ddp->d_name = strdup(dirname);
        //attention! There is a malloc in strdup
        if(ddp->d_name == NULL)
        {
                free(ddp);
                return;
        }

        ddp->d_next = NULL;

        if(tail == NULL)
        {
                head = ddp;
                tail = ddp;
        }
        else
        {
                tail->d_next = ddp;
                tail = ddp;
        }
}

static void cleanup(void)
{
        struct devdir *ddp,*nddp;

        ddp = head;
        while(ddp != NULL)
        {
                nddp = ddp->d_next;
                free(ddp->d_name);
                free(ddp);
                ddp = nddp;
        }

        head = NULL;
        tail = NULL;
}

static char* searchdir(char* dirname,struct stat* fdstatp)
{
        struct stat     devstat;
        DIR             *dp;
        int             devlen;
        struct dirent*  dirp;

        strcpy(pathname,dirname);

        if((dp = opendir(dirname)) == NULL)
        {
                return NULL;
        }

        strcat(pathname,"/");

        devlen = strlen(pathname);
        while((dirp = readdir(dp)) != NULL)
        {
                strncpy(pathname + devlen,dirp->d_name,_POSIX_PATH_MAX - devlen);
                if(strcmp(pathname,"/dev/stdin") == 0 || strcmp(pathname,"/dev/stdout") == 0 || strcmp(pathname,"/dev/stderr") == 0)
                {
                        continue;
                }

                if(stat(pathname,&devstat) < 0)
                {
		           continue;
                }

                if(S_ISDIR(devstat.st_mode))
                {
                        add(pathname);
                        continue;
                }

                if(devstat.st_ino == fdstatp->st_ino && devstat.st_dev == fdstatp->st_dev)
                {
                        closedir(dp);
                        return pathname;
                }
        }

        closedir(dp);
        return NULL;
}

char* tty(int fd)
{
        struct stat   fdstat;
        struct devdir *ddp;
        char          *rval;

        if(isatty(fd) == 0)
        {
                return NULL;
        }

        if(fstat(fd,&fdstat) < 0)
        {
                return NULL;
        }

        if(S_ISCHR(fdstat.st_mode) == 0)
        {
                return NULL;
        }

        rval = searchdir("/dev",&fdstat);

        if(rval == NULL)
        {
                for(ddp = head; ddp != NULL ; ddp = ddp->d_next)
                {
                        if((rval = searchdir(ddp->d_name,&fdstat)) != NULL)
                        {
                                break;
                        }
                }
        }

        cleanup();
        return rval;
}

/************************************************************
code writer : EOF
code date   : 2014.04.15 00:32
e-mail      : [email protected]
code purpose:

        Just a demo for ourselves‘ ttyname--tty.There would 
be conflict with libc when we use our function‘s name 
as ttyname. So I change the name of the function into tty.
It‘s Nothing.

***********************************************************/
#include <stdio.h>
#include </Ad_Pro_in_Unix/chapter_18/pro_18_15.c>

int main()
{
        char* name;

        if(isatty(0))
        {
                name = tty(0);
                if(name == NULL)
                {
                        name = "undefined\n";
                }
        }
        else
        {
                name = "not a tty\n";
        }

        printf("fd 0 :%s\n",name);

        if(isatty(1))
        {
                name = tty(1);
                if(name == NULL)
                {
                        name = "undefined\n";
                }
        }
        else
        {
                name = "not a tty\n";
        }

        printf("fd 1 :%s\n",name);

        if(isatty(2))
        {
                name = tty(2);
                if(name == NULL)
                {
                        name = "undefined\n";
                }
        }
        else
        {
                name = "not a tty\n";
        }

        printf("fd 2 :%s\n",name); 
        return 0;

}

liuzjian@ubuntu:/Ad_Pro_in_Unix/chapter_18$ ./a.out
fd 0 :/dev/pts/0
fd 1 :/dev/pts/0
fd 2 :/dev/pts/0

这三行简单的输出。。。我调了多久。。。。T-T

Canonical Mode

?The read returns when the requested number of bytes have been read.  We don’t have to read a complete line. If we read a partial line, no information is lost; the next read starts where the previous read stopped.

?The read returns when a line delimiter is encountered.  Recall from Section 18.3 that  the  following  characters are interpreted  as  end  of  line  in  canonical  mode: NL, EOL, EOL2, and EOF. Also, recall from Section 18.5 that if ICRNL is set and if IGNCR is not set, then the CR character also terminates a line, since it acts just

like the NL character. Of these five line delimiters, one(EOF ) is discarded by the terminal driver when it’s processed.  The other  four  ar ereturned  to  the  caller  as  the  last  character  of the line.

?The read also returns if a signal is caught and if the function is not automatically restarted (Section 10.5).

#include <signal.h>
#include <stdio.h>
#include <termios.h>

#define MAX_PASS_LEN    8

char* getpass(const char* prompt)
{
        static char     buf[MAX_PASS_LEN + 1];
        char            *ptr;
        sigset_t        sig,osig;
        struct termios  ts,ots;
        FILE            *fp;
        int             c;

        if((fp = fopen(ctermid(NULL),"r+")) == NULL)
        {
                return NULL;
        }

        setbuf(fp,NULL);//unbuffer

        sigemptyset(&sig);
        sigemptyset(&osig);
        sigaddset(&sig,SIGINT);
        sigaddset(&sig,SIGTSTP);
        sigprocmask(SIG_BLOCK,&sig,&osig);

        tcgetattr(fileno(fp),&ts);
        ots = ts;
        ts.c_lflag &= ~(ECHO | ECHOE | ECHOK | ECHONL);
        tcsetattr(fileno(fp),TCSAFLUSH,&ts);
        fputs(prompt,fp);

        ptr = buf;
        while((c = getc(fp)) != EOF && c != ‘\n‘)
        {
                if(ptr < &buf[MAX_PASS_LEN])
                {
                        *ptr++ = c;
                }
        }

        *ptr = 0;//equivalent to ptr = NULL

        putc(‘\n‘,fp);
        tcsetattr(fileno(fp),TCSAFLUSH,&ots);
        sigprocmask(SIG_SETMASK,&osig,NULL);
        fclose(fp);

        return buf;
}

#include <stdio.h>
#include </Ad_Pro_in_Unix/chapter_18/pro_18_17.c>

int main()
{
        char *ptr;

        if((ptr = getpass("Enter password:")) == NULL)
        {
                printf("getpass error\n");
        }

        printf("password:%s\n",ptr);

        while(*ptr != 0)
        {
                *ptr++ = 0;
        }

        return 0;
}

#define MAX_PASS_LEN    8

static char     buf[MAX_PASS_LEN + 1];

Noncanonical Mode

Terminal  Window Size

struct winsize
  {
    unsigned short int ws_row;
    unsigned short int ws_col;
    unsigned short int ws_xpixel;
    unsigned short int ws_ypixel;
  };

#include <termios.h>
#include <signal.h>
#include <unistd.h>
#include <stdio.h>

#ifndef TIOCGWINSZ
        #include <sys/ioctl.h>
#endif

static void pr_winsize(int fd)
{
        struct winsize size;

        if(ioctl(fd,TIOCGWINSZ,(char *)&size) < 0)
        {
                printf("ioctl error\n");
        }

        printf("%d rows, %d columns\n",size.ws_row,size.ws_col);
}

static void sig_winch(int signo)
{
        printf("SIGWINCH received\n");
        pr_winsize(STDIN_FILENO);
}

int main()
{
        struct sigaction sa;

        sigemptyset(&sa.sa_mask);
        sa.sa_flags = 0;
        sa.sa_handler = sig_winch;

        if(isatty(STDIN_FILENO) == 0)
        {
                return 1;
        }

        if(sigaction(SIGWINCH,&sa,NULL) < 0)
        {
                printf("sigaction error\n");
        }

        pr_winsize(STDIN_FILENO);

        for(;;)
        {
                pause();
        }

        return 0;
}

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