TTY终端的输入过程

TTY终端的输入过程
=================
1) 当用户按压键盘时, 键盘中断处理程序将经过转换的键盘功能码用tty_insert_flip_char()放入到当前打开终端的翻转缓冲区之中, 
然后将缓冲区输出任务函数(flush_to_ldisc)添加到控制台任务队列(con_task_queue)并激活控制台软中断执行该任务函数. flush_to_ldisc()翻转读写缓冲区,
 将缓冲区接收数据传递给tty终端规程的n_tty_receive_buf()接收函数, n_tty_receive_buf()处理输入字符, 将输出字符缓冲在终端的循环缓冲区(read_buf)之中.
 用户通过tty规程的read_chan()读取read_buf中的字符. 当多个进程同时读取同一终端时, 使用tty->atomic_read信号灯来竞争读取权. 


2) 每一打开的终端接口中包含终端的参数结构(termios), 当终端打开时, 它将继承终端驱动设备参数表中参数结构, 系统缺省的终端参数为tty_std_termios,
 驱动设备的初始终端参数为init_termios. 终端参数可由用户通过ioctl()调整, 用来控制终端接口的行为. c_iflag描述对输入字符的识别模式, 
c_oflag描述对输出字符的处理模式, c_cflag描述终端接口的控制模式, c_lflag描述字符处理过程中各种本地行为, 还有由19个字符组成的c_cc字符参数表, 
描述各类控制字符以及辅助参数. 

3) 当本地模式具有规范输入标志(ICANON)时, 输出数据按行拷贝给用户. 在接收到换行符(或者文件结束符c_cc[VEOF],行结束符c_cc[VEOL]和c_cc[VEOL2])之前, 
可以使用编辑控制符完成简单的编辑. c_cc[VERASE]删除前一字符, c_cc[VKILL]删除整行, c_cc[VWERASE]删除前一单词. 

4) 当本地模式具有回显标志(ECHO)时, 输入字符按一定的规则回显到输出设备上. 当本地模式具有信号标志(ISIG)时, 特定的输入字符可以在终端当前进程组中产生信号.
 c_cc[VINTR]产生中断信号, c_cc[VQUIT]产生退出信息, c_cc[VSUSP]产生暂停信号. c_cc[VTIME]定义了用户读取数据的等待超时, 单位为0.1秒, 
c_cc[VMIN]为所期望的字节数. 在非ICANON模式下, 如果在c_cc[VTIME]时间内接收到c_cc[VMIN]数量的字符, 读过程返回. c_cc[VSTOP]暂停驱动设备输出, 
c_cc[VSTART]启动驱动设备输出. 

5) 内核初始化结束后, 打开控制台终端设备/dev/console作为输入输出去运行/sbin/init. /dev/console的设备号是0x0501, 
在打开时被定向到命令行(console=)指定的终端设备, 缺省情况下为/dev/tty1, 其设备号为0x0401. init程序完成用户初始化完成后启动若干个终端守护程序(getty).
 getty在打开所守护的终端文件之前先使用setsid()创建会话组并成为会话组的首领进程(leader=1), 首领进程的会话号(session)和进程组号(pgrp)等于进程号(pid).
 首领进程打开终端文件后成为终端的控制进程, 其tty指针指向该终端打开结构, 该终端也成为本次会话的控制终端, 
其session号和pgrp号分别等于进程的session号和pgrp号. 当用户从终端登录后, 登录bash程序置换getty进程成为首领进程. 
进程的会话号和组号随着进程的复制而传递, 子进程的首领标志复位.
 bash在用execve()执行用户程序之前将用setpgid()为每一程序建立属于它自已的进程组(使进程组号等于进程号), 
再用对终端的(TIOCSPGRP)设备控制将终端进程组号设为将该进程号, 使终端切换到新的进程组. 
终端进程组以外的进程组如果进行读操作将在其进程组中生成SIGTTIN信号, 缺省的信号处理器使进程进入暂停. 

; drivers/char/keyboard.c:

void put_queue(int ch)
{
	wake_up(&keypress_wait);
	if (tty) {
		tty_insert_flip_char(tty, ch, 0);
		con_schedule_flip(tty);
	}
}
static void puts_queue(char *cp)
{
	wake_up(&keypress_wait);
	if (!tty)
		return;

	while (*cp) {
		tty_insert_flip_char(tty, *cp, 0);
		cp++;
	}
	con_schedule_flip(tty);
}
_INLINE_ void tty_insert_flip_char(struct tty_struct *tty,
				   unsigned char ch, char flag)
{
	if (tty->flip.count < TTY_FLIPBUF_SIZE) {
		tty->flip.count++;
		*tty->flip.flag_buf_ptr++ = flag;
		*tty->flip.char_buf_ptr++ = ch;
	}
}
extern inline void con_schedule_flip(struct tty_struct *t)
{
	queue_task(&t->flip.tqueue, &con_task_queue);
	tasklet_schedule(&console_tasklet);
}


; drivers/char/tty_io.c:

/*
 * When a break, frame error, or parity error happens, these codes are
 * stuffed into the flags buffer.
 */
#define TTY_NORMAL	0
#define TTY_BREAK	1
#define TTY_FRAME	2
#define TTY_PARITY	3
#define TTY_OVERRUN	4

#define INTR_CHAR(tty) ((tty)->termios->c_cc[VINTR])
#define QUIT_CHAR(tty) ((tty)->termios->c_cc[VQUIT])
#define ERASE_CHAR(tty) ((tty)->termios->c_cc[VERASE])
#define KILL_CHAR(tty) ((tty)->termios->c_cc[VKILL])
#define EOF_CHAR(tty) ((tty)->termios->c_cc[VEOF])
#define TIME_CHAR(tty) ((tty)->termios->c_cc[VTIME])
#define MIN_CHAR(tty) ((tty)->termios->c_cc[VMIN])
#define SWTC_CHAR(tty) ((tty)->termios->c_cc[VSWTC])
#define START_CHAR(tty) ((tty)->termios->c_cc[VSTART])
#define STOP_CHAR(tty) ((tty)->termios->c_cc[VSTOP])
#define SUSP_CHAR(tty) ((tty)->termios->c_cc[VSUSP])
#define EOL_CHAR(tty) ((tty)->termios->c_cc[VEOL])
#define REPRINT_CHAR(tty) ((tty)->termios->c_cc[VREPRINT])
#define DISCARD_CHAR(tty) ((tty)->termios->c_cc[VDISCARD])
#define WERASE_CHAR(tty) ((tty)->termios->c_cc[VWERASE])
#define LNEXT_CHAR(tty)	((tty)->termios->c_cc[VLNEXT])
#define EOL2_CHAR(tty) ((tty)->termios->c_cc[VEOL2])

#define _I_FLAG(tty,f)	((tty)->termios->c_iflag & (f))
#define _O_FLAG(tty,f)	((tty)->termios->c_oflag & (f))
#define _C_FLAG(tty,f)	((tty)->termios->c_cflag & (f))
#define _L_FLAG(tty,f)	((tty)->termios->c_lflag & (f))

#define I_IGNBRK(tty)	_I_FLAG((tty),IGNBRK)
#define I_BRKINT(tty)	_I_FLAG((tty),BRKINT)
#define I_IGNPAR(tty)	_I_FLAG((tty),IGNPAR)
#define I_PARMRK(tty)	_I_FLAG((tty),PARMRK)
#define I_INPCK(tty)	_I_FLAG((tty),INPCK)
#define I_ISTRIP(tty)	_I_FLAG((tty),ISTRIP)
#define I_INLCR(tty)	_I_FLAG((tty),INLCR)
#define I_IGNCR(tty)	_I_FLAG((tty),IGNCR)
#define I_ICRNL(tty)	_I_FLAG((tty),ICRNL)
#define I_IUCLC(tty)	_I_FLAG((tty),IUCLC)
#define I_IXON(tty)	_I_FLAG((tty),IXON)
#define I_IXANY(tty)	_I_FLAG((tty),IXANY)
#define I_IXOFF(tty)	_I_FLAG((tty),IXOFF)
#define I_IMAXBEL(tty)	_I_FLAG((tty),IMAXBEL)

#define O_OPOST(tty)	_O_FLAG((tty),OPOST)
#define O_OLCUC(tty)	_O_FLAG((tty),OLCUC)
#define O_ONLCR(tty)	_O_FLAG((tty),ONLCR)
#define O_OCRNL(tty)	_O_FLAG((tty),OCRNL)
#define O_ONOCR(tty)	_O_FLAG((tty),ONOCR)
#define O_ONLRET(tty)	_O_FLAG((tty),ONLRET)
#define O_OFILL(tty)	_O_FLAG((tty),OFILL)
#define O_OFDEL(tty)	_O_FLAG((tty),OFDEL)
#define O_NLDLY(tty)	_O_FLAG((tty),NLDLY)
#define O_CRDLY(tty)	_O_FLAG((tty),CRDLY)
#define O_TABDLY(tty)	_O_FLAG((tty),TABDLY)
#define O_BSDLY(tty)	_O_FLAG((tty),BSDLY)
#define O_VTDLY(tty)	_O_FLAG((tty),VTDLY)
#define O_FFDLY(tty)	_O_FLAG((tty),FFDLY)

#define C_BAUD(tty)	_C_FLAG((tty),CBAUD)
#define C_CSIZE(tty)	_C_FLAG((tty),CSIZE)
#define C_CSTOPB(tty)	_C_FLAG((tty),CSTOPB)
#define C_CREAD(tty)	_C_FLAG((tty),CREAD)
#define C_PARENB(tty)	_C_FLAG((tty),PARENB)
#define C_PARODD(tty)	_C_FLAG((tty),PARODD)
#define C_HUPCL(tty)	_C_FLAG((tty),HUPCL)
#define C_CLOCAL(tty)	_C_FLAG((tty),CLOCAL)
#define C_CIBAUD(tty)	_C_FLAG((tty),CIBAUD)
#define C_CRTSCTS(tty)	_C_FLAG((tty),CRTSCTS)

#define L_ISIG(tty)	_L_FLAG((tty),ISIG)
#define L_ICANON(tty)	_L_FLAG((tty),ICANON)
#define L_XCASE(tty)	_L_FLAG((tty),XCASE)
#define L_ECHO(tty)	_L_FLAG((tty),ECHO)
#define L_ECHOE(tty)	_L_FLAG((tty),ECHOE)
#define L_ECHOK(tty)	_L_FLAG((tty),ECHOK)
#define L_ECHONL(tty)	_L_FLAG((tty),ECHONL)
#define L_NOFLSH(tty)	_L_FLAG((tty),NOFLSH)
#define L_TOSTOP(tty)	_L_FLAG((tty),TOSTOP)
#define L_ECHOCTL(tty)	_L_FLAG((tty),ECHOCTL)
#define L_ECHOPRT(tty)	_L_FLAG((tty),ECHOPRT)
#define L_ECHOKE(tty)	_L_FLAG((tty),ECHOKE)
#define L_FLUSHO(tty)	_L_FLAG((tty),FLUSHO)
#define L_PENDIN(tty)	_L_FLAG((tty),PENDIN)
#define L_IEXTEN(tty)	_L_FLAG((tty),IEXTEN)

/* number of characters left in xmit buffer before select has we have room */
#define WAKEUP_CHARS 256

typedef unsigned char	cc_t;
typedef unsigned int	speed_t;
typedef unsigned int	tcflag_t;

#define NCCS 19
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 */
};

/*	intr=^C		quit=^\		erase=del	kill=^U
	eof=^D		vtime=\0	vmin=\1		sxtc=\0
	start=^Q	stop=^S		susp=^Z		eol=\0
	reprint=^R	discard=^U	werase=^W	lnext=^V
	eol2=\0
*/
#define INIT_C_CC "\003\034\177\025\004\0\1\0\021\023\032\0\022\017\027\026\0"

/* 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

/* c_iflag bits */
#define IGNBRK	0000001
#define BRKINT	0000002
#define IGNPAR	0000004
#define PARMRK	0000010
#define INPCK	0000020
#define ISTRIP	0000040
#define INLCR	0000100
#define IGNCR	0000200
#define ICRNL	0000400
#define IUCLC	0001000
#define IXON	0002000
#define IXANY	0004000
#define IXOFF	0010000
#define IMAXBEL	0020000

/* c_oflag bits */
#define OPOST	0000001
#define OLCUC	0000002
#define ONLCR	0000004
#define OCRNL	0000010
#define ONOCR	0000020
#define ONLRET	0000040
#define OFILL	0000100
#define OFDEL	0000200
#define NLDLY	0000400
#define   NL0	0000000
#define   NL1	0000400
#define CRDLY	0003000
#define   CR0	0000000
#define   CR1	0001000
#define   CR2	0002000
#define   CR3	0003000
#define TABDLY	0014000
#define   TAB0	0000000
#define   TAB1	0004000
#define   TAB2	0010000
#define   TAB3	0014000
#define   XTABS	0014000
#define BSDLY	0020000
#define   BS0	0000000
#define   BS1	0020000
#define VTDLY	0040000
#define   VT0	0000000
#define   VT1	0040000
#define FFDLY	0100000
#define   FF0	0000000
#define   FF1	0100000

/* c_cflag bit meaning */
#define CBAUD	0010017
#define  B0	0000000		/* hang up */
#define  B50	0000001
#define  B75	0000002
#define  B110	0000003
#define  B134	0000004
#define  B150	0000005
#define  B200	0000006
#define  B300	0000007
#define  B600	0000010
#define  B1200	0000011
#define  B1800	0000012
#define  B2400	0000013
#define  B4800	0000014
#define  B9600	0000015
#define  B19200	0000016
#define  B38400	0000017
#define EXTA B19200
#define EXTB B38400
#define CSIZE	0000060
#define   CS5	0000000
#define   CS6	0000020
#define   CS7	0000040
#define   CS8	0000060
#define CSTOPB	0000100
#define CREAD	0000200
#define PARENB	0000400
#define PARODD	0001000
#define HUPCL	0002000
#define CLOCAL	0004000
#define CBAUDEX 0010000
#define    B57600 0010001
#define   B115200 0010002
#define   B230400 0010003
#define   B460800 0010004
#define   B500000 0010005
#define   B576000 0010006
#define   B921600 0010007
#define  B1000000 0010010
#define  B1152000 0010011
#define  B1500000 0010012
#define  B2000000 0010013
#define  B2500000 0010014
#define  B3000000 0010015
#define  B3500000 0010016
#define  B4000000 0010017
#define CIBAUD	  002003600000	/* input baud rate (not used) */
#define CMSPAR	  010000000000		/* mark or space (stick) parity */
#define CRTSCTS	  020000000000		/* flow control */

/* c_lflag bits */
#define ISIG	0000001
#define ICANON	0000002
#define XCASE	0000004
#define ECHO	0000010
#define ECHOE	0000020
#define ECHOK	0000040
#define ECHONL	0000100
#define NOFLSH	0000200
#define TOSTOP	0000400
#define ECHOCTL	0001000
#define ECHOPRT	0002000
#define ECHOKE	0004000
#define FLUSHO	0010000
#define PENDIN	0040000
#define IEXTEN	0100000

/*
 * This defines the low- and high-watermarks for throttling and
 * unthrottling the TTY driver.  These watermarks are used for
 * controlling the space in the read buffer.
 */
#define TTY_THRESHOLD_THROTTLE		128 /* now based on remaining room */
#define TTY_THRESHOLD_UNTHROTTLE 	128

static struct file_operations tty_fops = {
	llseek:		tty_lseek,
	read:		tty_read,
	write:		tty_write,
	poll:		tty_poll,
	ioctl:		tty_ioctl,
	open:		tty_open,
	release:	tty_release,
	fasync:		tty_fasync,
};

void __init console_init(void)
{
	/* Setup the default TTY line discipline. */
	memset(ldiscs, 0, sizeof(ldiscs));
	(void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);

	/*
	 * Set up the standard termios.  Individual tty drivers may 
	 * deviate from this; this is used as a template.
	 */
	memset(&tty_std_termios, 0, sizeof(struct termios));
	memcpy(tty_std_termios.c_cc, INIT_C_CC, NCCS);
	tty_std_termios.c_iflag = ICRNL | IXON;
	tty_std_termios.c_oflag = OPOST | ONLCR;
	tty_std_termios.c_cflag = B38400 | CS8 | CREAD | HUPCL;
	tty_std_termios.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK |
		ECHOCTL | ECHOKE | IEXTEN;

	...
}

static ssize_t tty_read(struct file * file, char * buf, size_t count, 
			loff_t *ppos)
{
	int i;
	struct tty_struct * tty;
	struct inode *inode;

	/* Can't seek (pread) on ttys.  */
	if (ppos != &file->f_pos)
		return -ESPIPE;

	tty = (struct tty_struct *)file->private_data;
	inode = file->f_dentry->d_inode;
	if (tty_paranoia_check(tty, inode->i_rdev, "tty_read")) 校验tty结构是否完整
		return -EIO;
	if (!tty || (test_bit(TTY_IO_ERROR, &tty->flags)))
		return -EIO;

	/* This check not only needs to be done before reading, but also
	   whenever read_chan() gets woken up after sleeping, so I've
	   moved it to there.  This should only be done for the N_TTY
	   line discipline, anyway.  Same goes for write_chan(). -- jlc. */
#if 0
	if ((inode->i_rdev != CONSOLE_DEV) && /* don't stop on /dev/console */
	    (tty->pgrp > 0) &&
	    (current->tty == tty) &&
	    (tty->pgrp != current->pgrp))
		if (is_ignored(SIGTTIN) || is_orphaned_pgrp(current->pgrp))
			return -EIO;
		else {
			(void) kill_pg(current->pgrp, SIGTTIN, 1);
			return -ERESTARTSYS;
		}
#endif
	lock_kernel();
	if (tty->ldisc.read)
		i = (tty->ldisc.read)(tty,file,buf,count);
	else
		i = -EIO;
	unlock_kernel();
	if (i > 0)
		inode->i_atime = CURRENT_TIME;
	return i;
}

/*
 * This routine is called out of the software interrupt to flush data
 * from the flip buffer to the line discipline.
 */
static void flush_to_ldisc(void *private_)
{
	struct tty_struct *tty = (struct tty_struct *) private_;
	unsigned char	*cp;
	char		*fp;
	int		count;
	unsigned long flags;

	if (test_bit(TTY_DONT_FLIP, &tty->flags)) { 如果不允许翻转读写缓冲区
		queue_task(&tty->flip.tqueue, &tq_timer); 将任务延迟一个时钟中断
		return;
	}
	if (tty->flip.buf_num) {
		cp = tty->flip.char_buf + TTY_FLIPBUF_SIZE;
		fp = tty->flip.flag_buf + TTY_FLIPBUF_SIZE;
		tty->flip.buf_num = 0;

		save_flags(flags); cli();
		tty->flip.char_buf_ptr = tty->flip.char_buf;
		tty->flip.flag_buf_ptr = tty->flip.flag_buf;
	} else {
		cp = tty->flip.char_buf;
		fp = tty->flip.flag_buf;
		tty->flip.buf_num = 1;

		save_flags(flags); cli();
		tty->flip.char_buf_ptr = tty->flip.char_buf + TTY_FLIPBUF_SIZE;
		tty->flip.flag_buf_ptr = tty->flip.flag_buf + TTY_FLIPBUF_SIZE;
	}
	count = tty->flip.count;
	tty->flip.count = 0;
	restore_flags(flags);
	
	tty->ldisc.receive_buf(tty, cp, fp, count);
}
void start_tty(struct tty_struct *tty)
{
	if (!tty->stopped || tty->flow_stopped)
		return;
	tty->stopped = 0;
	if (tty->link && tty->link->packet) {
		tty->ctrl_status &= ~TIOCPKT_STOP;
		tty->ctrl_status |= TIOCPKT_START;
		wake_up_interruptible(&tty->link->read_wait);
	}
	if (tty->driver.start)
		(tty->driver.start)(tty);
	if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
	    tty->ldisc.write_wakeup)
		(tty->ldisc.write_wakeup)(tty);
	wake_up_interruptible(&tty->write_wait);
}
void stop_tty(struct tty_struct *tty)
{
	if (tty->stopped)
		return;
	tty->stopped = 1;
	if (tty->link && tty->link->packet) { 
		tty->ctrl_status &= ~TIOCPKT_START; 
		tty->ctrl_status |= TIOCPKT_STOP; 
		wake_up_interruptible(&tty->link->read_wait);
	}
	if (tty->driver.stop)
		(tty->driver.stop)(tty);
}
; drivers/char/n_tty.c:

struct tty_ldisc tty_ldisc_N_TTY = {
	TTY_LDISC_MAGIC,	/* magic */
	"n_tty",		/* name */
	0,			/* num */
	0,			/* flags */
	n_tty_open,		/* open */
	n_tty_close,		/* close */
	n_tty_flush_buffer,	/* flush_buffer */
	n_tty_chars_in_buffer,	/* chars_in_buffer */
	read_chan,		/* read */
	write_chan,		/* write */
	n_tty_ioctl,		/* ioctl */
	n_tty_set_termios,	/* set_termios */
	normal_poll,		/* poll */
	n_tty_receive_buf,	/* receive_buf */
	n_tty_receive_room,	/* receive_room */
	0			/* write_wakeup */
};

static ssize_t read_chan(struct tty_struct *tty, struct file *file,
			 unsigned char *buf, size_t nr)
{
	unsigned char *b = buf;
	DECLARE_WAITQUEUE(wait, current);
	int c;
	int minimum, time;
	ssize_t retval = 0;
	ssize_t size;
	long timeout;
	unsigned long flags;

do_it_again:

	if (!tty->read_buf) {
		printk("n_tty_read_chan: called with read_buf == NULL?!?\n");
		return -EIO;
	}

	/* Job control check -- must be done at start and after
	   every sleep (POSIX.1 7.1.1.4). */
	/* NOTE: not yet done after every sleep pending a thorough
	   check of the logic of this change. -- jlc */
	/* don't stop on /dev/console */
	if (file->f_dentry->d_inode->i_rdev != CONSOLE_DEV && 打开的不是/dev/tty设备
	    file->f_dentry->d_inode->i_rdev != SYSCONS_DEV && 打开的不是/dev/console设备
	    current->tty == tty) { 
		if (tty->pgrp <= 0)
			printk("read_chan: tty->pgrp <= 0!\n");
		else if (current->pgrp != tty->pgrp) { 如果当前进程不属于终端的当前进程组
			if (is_ignored(SIGTTIN) || 如果SIGTTIN信号被忽略
			    is_orphaned_pgrp(current->pgrp)) 如果当前进程组的父进程已退出
				return -EIO;
			kill_pg(current->pgrp, SIGTTIN, 1); 
			return -ERESTARTSYS;
		}
	}

	minimum = time = 0;
	timeout = MAX_SCHEDULE_TIMEOUT;
	if (!tty->icanon) { 如果不是规范输入模式
		time = (HZ / 10) * TIME_CHAR(tty); 计算超时时间, 时间字节的单位为0.1秒
		minimum = MIN_CHAR(tty); 返回的最少字符数
		if (minimum) { 
			if (time) 
				tty->minimum_to_wake = 1; 接收到1个字符后就唤醒
			else if (!waitqueue_active(&tty->read_wait) ||
				 (tty->minimum_to_wake > minimum))
				tty->minimum_to_wake = minimum;
		} else { 如果最少返回字符为零
			timeout = 0; 
			if (time) {
				timeout = time;
				time = 0;
			}
			tty->minimum_to_wake = minimum = 1;
		}
	}

	if (file->f_flags & O_NONBLOCK) {
		if (down_trylock(&tty->atomic_read))
			return -EAGAIN;
	}
	else {
		if (down_interruptible(&tty->atomic_read))
			return -ERESTARTSYS;
	}

	add_wait_queue(&tty->read_wait, &wait);
	set_bit(TTY_DONT_FLIP, &tty->flags); 禁止缓冲区翻转
	while (nr) {
		/* First test for status change. */
		if (tty->packet && tty->link->ctrl_status) {
			unsigned char cs;
			if (b != buf)
				break;
			cs = tty->link->ctrl_status;
			tty->link->ctrl_status = 0;
			put_user(cs, b++); 
			nr--;
			break; 
		}
		/* This statement must be first before checking for input
		   so that any interrupt will set the state back to
		   TASK_RUNNING. */
		set_current_state(TASK_INTERRUPTIBLE);
		
		if (((minimum - (b - buf)) < tty->minimum_to_wake) &&
		    ((minimum - (b - buf)) >= 1))
			tty->minimum_to_wake = (minimum - (b - buf));
		
		if (!input_available_p(tty, 0)) {
			if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
				retval = -EIO;
				break;
			}
			if (tty_hung_up_p(file))
				break;
			if (!timeout)
				break;
			if (file->f_flags & O_NONBLOCK) {
				retval = -EAGAIN;
				break;
			}
			if (signal_pending(current)) {
				retval = -ERESTARTSYS;
				break;
			}
			clear_bit(TTY_DONT_FLIP, &tty->flags);
			timeout = schedule_timeout(timeout);
			set_bit(TTY_DONT_FLIP, &tty->flags);
			continue;
		}
		current->state = TASK_RUNNING;

		/* Deal with packet mode. */
		if (tty->packet && b == buf) {
			put_user(TIOCPKT_DATA, b++);
			nr--;
		}

		if (tty->icanon) {
			/* N.B. avoid overrun if nr == 0 */
			while (nr && tty->read_cnt) {
 				int eol;

				eol = test_and_clear_bit(tty->read_tail,
						&tty->read_flags);
				c = tty->read_buf[tty->read_tail];
				spin_lock_irqsave(&tty->read_lock, flags);
				tty->read_tail = ((tty->read_tail+1) &
						  (N_TTY_BUF_SIZE-1));
				tty->read_cnt--;
				if (eol) {
					/* this test should be redundant:
					 * we shouldn't be reading data if
					 * canon_data is 0
					 */
					if (--tty->canon_data < 0)
						tty->canon_data = 0;
				}
				spin_unlock_irqrestore(&tty->read_lock, flags);

				if (!eol || (c != __DISABLED_CHAR)) {
					put_user(c, b++);
					nr--;
				}
				if (eol)
					break;
			}
		} else {
			int uncopied;
			uncopied = copy_from_read_buf(tty, &b, &nr);
			uncopied += copy_from_read_buf(tty, &b, &nr);
			if (uncopied) {
				retval = -EFAULT;
				break;
			}
		}

		/* If there is enough space in the read buffer now, let the
		 * low-level driver know. We use n_tty_chars_in_buffer() to
		 * check the buffer, as it now knows about canonical mode.
		 * Otherwise, if the driver is throttled and the line is
		 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
		 * we won't get any more characters.
		 */
		if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
			check_unthrottle(tty); 如果读缓冲区的字符小于128, 打开节流的输入设备

		if (b - buf >= minimum)
			break;
		if (time)
			timeout = time;
	}
	clear_bit(TTY_DONT_FLIP, &tty->flags);
	up(&tty->atomic_read);
	remove_wait_queue(&tty->read_wait, &wait);

	if (!waitqueue_active(&tty->read_wait))
		tty->minimum_to_wake = minimum;

	current->state = TASK_RUNNING;
	size = b - buf;
	if (size) {
		retval = size;
		if (nr)
	       		clear_bit(TTY_PUSH, &tty->flags);
	} else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
		 goto do_it_again;

	return retval;
}
int is_ignored(int sig)
{
	return (sigismember(¤t->blocked, sig) ||
	        current->sig->action[sig-1].sa.sa_handler == SIG_IGN);
}

static inline int input_available_p(struct tty_struct *tty, int amt)
{
	if (tty->icanon) {
		if (tty->canon_data)
			return 1;
	} else if (tty->read_cnt >= (amt ? amt : 1))
		return 1;

	return 0;
}
int tty_hung_up_p(struct file * filp)
{
	return (filp->f_op == &hung_up_tty_fops);
}
/*
 * Helper function to speed up read_chan.  It is only called when
 * ICANON is off; it copies characters straight from the tty queue to
 * user space directly.  It can be profitably called twice; once to
 * drain the space from the tail pointer to the (physical) end of the
 * buffer, and once to drain the space from the (physical) beginning of
 * the buffer to head pointer.
 */
static inline int copy_from_read_buf(struct tty_struct *tty,
				      unsigned char **b,
				      size_t *nr)

{
	int retval;
	ssize_t n;
	unsigned long flags;

	retval = 0;
	spin_lock_irqsave(&tty->read_lock, flags);
	n = MIN(*nr, MIN(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail));
	spin_unlock_irqrestore(&tty->read_lock, flags);
	if (n) {
		mb();
		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
		n -= retval;
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt -= n;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		*b += n;
		*nr -= n;
	}
	return retval;
}
/*
 * Return number of characters buffered to be delivered to user
 */
ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
{
	unsigned long flags;
	ssize_t n = 0;

	spin_lock_irqsave(&tty->read_lock, flags);
	if (!tty->icanon) {
		n = tty->read_cnt;
	} else if (tty->canon_data) {
		n = (tty->canon_head > tty->read_tail) ?
			tty->canon_head - tty->read_tail :
			tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
	}
	spin_unlock_irqrestore(&tty->read_lock, flags);
	return n;
}

/* 
 * Check whether to call the driver.unthrottle function.
 * We test the TTY_THROTTLED bit first so that it always
 * indicates the current state.
 */
static void check_unthrottle(struct tty_struct * tty)
{
	if (tty->count &&
	    test_and_clear_bit(TTY_THROTTLED, &tty->flags) && 
	    tty->driver.unthrottle)
		tty->driver.unthrottle(tty);
}

static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
			      char *fp, int count)
{
	const unsigned char *p;
	char *f, flags = TTY_NORMAL;
	int	i;
	char	buf[64];
	unsigned long cpuflags;

	if (!tty->read_buf)
		return;

	if (tty->real_raw) { 如果终端处于原始接收模式, 直接输出翻转缓冲区字符
		spin_lock_irqsave(&tty->read_lock, cpuflags);
		i = MIN(count, MIN(N_TTY_BUF_SIZE - tty->read_cnt,
				   N_TTY_BUF_SIZE - tty->read_head));
		memcpy(tty->read_buf + tty->read_head, cp, i);
		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt += i;
		cp += i;
		count -= i;

		i = MIN(count, MIN(N_TTY_BUF_SIZE - tty->read_cnt,
			       N_TTY_BUF_SIZE - tty->read_head));
		memcpy(tty->read_buf + tty->read_head, cp, i);
		tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt += i;
		spin_unlock_irqrestore(&tty->read_lock, cpuflags);
	} else {
		for (i=count, p = cp, f = fp; i; i--, p++) {
			if (f)
				flags = *f++;
			switch (flags) {
			case TTY_NORMAL:
				n_tty_receive_char(tty, *p);
				break;
			case TTY_BREAK:
				n_tty_receive_break(tty);
				break;
			case TTY_PARITY:
			case TTY_FRAME:
				n_tty_receive_parity_error(tty, *p);
				break;
			case TTY_OVERRUN:
				n_tty_receive_overrun(tty);
				break;
			default:
				printk("%s: unknown flag %d\n",
				       tty_name(tty, buf), flags);
				break;
			}
		}
		if (tty->driver.flush_chars)
			tty->driver.flush_chars(tty);
	}

	if (!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) {
		kill_fasync(&tty->fasync, SIGIO, POLL_IN); 异步信号读写通知
		if (waitqueue_active(&tty->read_wait))
			wake_up_interruptible(&tty->read_wait);
	}

	/*
	 * Check the remaining room for the input canonicalization
	 * mode.  We don't want to throttle the driver if we're in
	 * canonical mode and don't have a newline yet!
	 */
	if (n_tty_receive_room(tty) < TTY_THRESHOLD_THROTTLE) { 如果剩余空间小于128字节
		/* check TTY_THROTTLED first so it indicates our state */
		if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
		    tty->driver.throttle)
			tty->driver.throttle(tty); 进行节流处理
	}
}
static inline void n_tty_receive_break(struct tty_struct *tty)
{
	if (I_IGNBRK(tty)) 如果忽略中断字符
		return;
	if (I_BRKINT(tty)) { 如果中断字符产生中信号
		isig(SIGINT, tty, 1); 给终端所在的进程组发送INT信号
		return;
	}
	if (I_PARMRK(tty)) { 断点标记
		put_tty_queue('\377', tty);
		put_tty_queue('\0', tty);
	}
	put_tty_queue('\0', tty);
	wake_up_interruptible(&tty->read_wait);
}

static inline void n_tty_receive_overrun(struct tty_struct *tty)
{
	char buf[64];

	tty->num_overrun++;
	if (time_before(tty->overrun_time, jiffies - HZ)) {
		printk("%s: %d input overrun(s)\n", tty_name(tty, buf),
		       tty->num_overrun);
		tty->overrun_time = jiffies;
		tty->num_overrun = 0;
	}
}

static inline void n_tty_receive_parity_error(struct tty_struct *tty,
					      unsigned char c)
{
	if (I_IGNPAR(tty)) {
		return;
	}
	if (I_PARMRK(tty)) {
		put_tty_queue('\377', tty);
		put_tty_queue('\0', tty);
		put_tty_queue(c, tty);
	} else	if (I_INPCK(tty)) 允许奇偶校验
		put_tty_queue('\0', tty);
	else
		put_tty_queue(c, tty);
	wake_up_interruptible(&tty->read_wait);
}

static int n_tty_receive_room(struct tty_struct *tty)
{
	int	left = N_TTY_BUF_SIZE - tty->read_cnt - 1;

	/*
	 * If we are doing input canonicalization, and there are no
	 * pending newlines, let characters through without limit, so
	 * that erase characters will be handled.  Other excess
	 * characters will be beeped.
	 */
	if (tty->icanon && !tty->canon_data)
		return N_TTY_BUF_SIZE;

	if (left > 0)
		return left;
	return 0;
}
static inline void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
{
	if (tty->read_cnt < N_TTY_BUF_SIZE) {
		tty->read_buf[tty->read_head] = c;
		tty->read_head = (tty->read_head + 1) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt++;
	}
}
static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
{
	unsigned long flags;

	if (tty->raw) {
		put_tty_queue(c, tty);
		return;
	}
	
	if (tty->stopped && !tty->flow_stopped &&
	    I_IXON(tty) && I_IXANY(tty)) { 如果软件流控制
		start_tty(tty);
		return;
	}
	
	if (I_ISTRIP(tty)) 如果去除字符最高位
		c &= 0x7f;
	if (I_IUCLC(tty) && L_IEXTEN(tty)) 如果允许小写转换扩展模式
		c=tolower(c);

	if (tty->closing) { 如果正在关闭终端
		if (I_IXON(tty)) {
			if (c == START_CHAR(tty))
				start_tty(tty);
			else if (c == STOP_CHAR(tty))
				stop_tty(tty);
		}
		return;
	}

	/*
	 * If the previous character was LNEXT, or we know that this
	 * character is not one of the characters that we'll have to
	 * handle specially, do shortcut processing to speed things
	 * up.
	 */
	if (!test_bit(c, &tty->process_char_map) || tty->lnext) {
		finish_erasing(tty);
		tty->lnext = 0;
		if (L_ECHO(tty)) { 如果输入字符回显
			if (tty->read_cnt >= N_TTY_BUF_SIZE-1) { 如果输入缓冲区满
				put_char('\a', tty); /* beep if no space */ 向显示终端发送响铃字符
				return;
			}
			/* Record the column of first canon char. */
			if (tty->canon_head == tty->read_head)
				tty->canon_column = tty->column;
			echo_char(c, tty);
		}
		if (I_PARMRK(tty) && c == (unsigned char) '\377')
			put_tty_queue(c, tty);
		put_tty_queue(c, tty);
		return;
	}
		
	if (c == '\r') {
		if (I_IGNCR(tty)) 忽略回车符
			return;
		if (I_ICRNL(tty)) 回车转换为换行符
			c = '\n';
	} else if (c == '\n' && I_INLCR(tty)) 换行符转换成回车符
		c = '\r';
	if (I_IXON(tty)) { 如果为软件流控
		if (c == START_CHAR(tty)) { 如果为启动字符
			start_tty(tty); 打开终端
			return;
		}
		if (c == STOP_CHAR(tty)) { 如果为停止字符
			stop_tty(tty); 暂停终端
			return;
		}
	}
	if (L_ISIG(tty)) { 如果允许触发信号
		int signal;
		signal = SIGINT;
		if (c == INTR_CHAR(tty)) 如果为中断字符
			goto send_signal;
		signal = SIGQUIT;
		if (c == QUIT_CHAR(tty)) 如果为退出字符
			goto send_signal;
		signal = SIGTSTP;
		if (c == SUSP_CHAR(tty)) { 如果为暂停字符
send_signal:
			isig(signal, tty, 0); 向终端所在的进程组发送相应的信号
			return;
		}
	}
	if (tty->icanon) { 
		if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
		    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) { 
			eraser(c, tty);
			return;
		}
		if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
			tty->lnext = 1;
			if (L_ECHO(tty)) {
				finish_erasing(tty);
				if (L_ECHOCTL(tty)) {
					put_char('^', tty);
					put_char('\b', tty);
				}
			}
			return;
		}
		if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
		    L_IEXTEN(tty)) {
			unsigned long tail = tty->canon_head;

			finish_erasing(tty);
			echo_char(c, tty);
			opost('\n', tty);
			while (tail != tty->read_head) {
				echo_char(tty->read_buf[tail], tty);
				tail = (tail+1) & (N_TTY_BUF_SIZE-1);
			}
			return;
		}
		if (c == '\n') {
			if (L_ECHO(tty) || L_ECHONL(tty)) {
				if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
					put_char('\a', tty);
					return;
				}
				opost('\n', tty);
			}
			goto handle_newline;
		}
		if (c == EOF_CHAR(tty)) {
		        if (tty->canon_head != tty->read_head)
			        set_bit(TTY_PUSH, &tty->flags);
			c = __DISABLED_CHAR;
			goto handle_newline;
		}
		if ((c == EOL_CHAR(tty)) ||
		    (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
			/*
			 * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
			 */
			if (L_ECHO(tty)) {
				if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
					put_char('\a', tty);
					return;
				}
				/* Record the column of first canon char. */
				if (tty->canon_head == tty->read_head)
					tty->canon_column = tty->column;
				echo_char(c, tty);
			}
			/*
			 * XXX does PARMRK doubling happen for
			 * EOL_CHAR and EOL2_CHAR?
			 */
			if (I_PARMRK(tty) && c == (unsigned char) '\377')
				put_tty_queue(c, tty);

		handle_newline:
			spin_lock_irqsave(&tty->read_lock, flags);
			set_bit(tty->read_head, &tty->read_flags);
			put_tty_queue_nolock(c, tty);
			tty->canon_head = tty->read_head;
			tty->canon_data++;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			kill_fasync(&tty->fasync, SIGIO, POLL_IN);
			if (waitqueue_active(&tty->read_wait))
				wake_up_interruptible(&tty->read_wait);
			return;
		}
	}
	
	finish_erasing(tty);
	if (L_ECHO(tty)) {
		if (tty->read_cnt >= N_TTY_BUF_SIZE-1) {
			put_char('\a', tty); /* beep if no space */
			return;
		}
		if (c == '\n')
			opost('\n', tty);
		else {
			/* Record the column of first canon char. */
			if (tty->canon_head == tty->read_head)
				tty->canon_column = tty->column;
			echo_char(c, tty);
		}
	}

	if (I_PARMRK(tty) && c == (unsigned char) '\377')
		put_tty_queue(c, tty);

	put_tty_queue(c, tty);
}	
static inline void put_char(unsigned char c, struct tty_struct *tty)
{
	tty->driver.put_char(tty, c);
}

/* Must be called only when L_ECHO(tty) is true. */

static void echo_char(unsigned char c, struct tty_struct *tty)
{
	if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') {
		put_char('^', tty); 回显控制字符
		put_char(c ^ 0100, tty);
		tty->column += 2;
	} else
		opost(c, tty); 回显字符
}

static inline void finish_erasing(struct tty_struct *tty)
{
	if (tty->erasing) {
		put_char('/', tty);
		tty->column += 2;
		tty->erasing = 0;
	}
}
static inline void isig(int sig, struct tty_struct *tty, int flush)
{
	if (tty->pgrp > 0)
		kill_pg(tty->pgrp, sig, 1);
	if (flush || !L_NOFLSH(tty)) {
		n_tty_flush_buffer(tty);
		if (tty->driver.flush_buffer)
			tty->driver.flush_buffer(tty);
	}
}
static void eraser(unsigned char c, struct tty_struct *tty)
{
	enum { ERASE, WERASE, KILL } kill_type;
	int head, seen_alnums;
	unsigned long flags;

	if (tty->read_head == tty->canon_head) { 如果输入为空
		/* opost('\a', tty); */		/* what do you think? */
		return;
	}
	if (c == ERASE_CHAR(tty))
		kill_type = ERASE;
	else if (c == WERASE_CHAR(tty))
		kill_type = WERASE;
	else { 
		if (!L_ECHO(tty)) { 如果禁止回显
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			return;
		}
		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
			spin_lock_irqsave(&tty->read_lock, flags);
			tty->read_cnt -= ((tty->read_head - tty->canon_head) &
					  (N_TTY_BUF_SIZE - 1));
			tty->read_head = tty->canon_head;
			spin_unlock_irqrestore(&tty->read_lock, flags);
			finish_erasing(tty);
			echo_char(KILL_CHAR(tty), tty);
			/* Add a newline if ECHOK is on and ECHOKE is off. */
			if (L_ECHOK(tty))
				opost('\n', tty);
			return;
		}
		kill_type = KILL;
	}

	seen_alnums = 0;
	while (tty->read_head != tty->canon_head) {
		head = (tty->read_head - 1) & (N_TTY_BUF_SIZE-1); 
		c = tty->read_buf[head];
		if (kill_type == WERASE) {
			/* Equivalent to BSD's ALTWERASE. */
			if (isalnum(c) || c == '_')
				seen_alnums++;
			else if (seen_alnums)
				break;
		}
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_head = head;
		tty->read_cnt--;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		if (L_ECHO(tty)) {
			if (L_ECHOPRT(tty)) {
				if (!tty->erasing) {
					put_char('\\', tty);
					tty->column++;
					tty->erasing = 1;
				}
				echo_char(c, tty);
			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
				echo_char(ERASE_CHAR(tty), tty);
			} else if (c == '\t') {
				unsigned int col = tty->canon_column;
				unsigned long tail = tty->canon_head;

				/* Find the column of the last char. */
				while (tail != tty->read_head) {
					c = tty->read_buf[tail];
					if (c == '\t')
						col = (col | 7) + 1;
					else if (iscntrl(c)) {
						if (L_ECHOCTL(tty))
							col += 2;
					} else
						col++;
					tail = (tail+1) & (N_TTY_BUF_SIZE-1);
				}

				/* should never happen */
				if (tty->column > 0x80000000)
					tty->column = 0; 

				/* Now backup to that column. */
				while (tty->column > col) {
					/* Can't use opost here. */
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
			} else {
				if (iscntrl(c) && L_ECHOCTL(tty)) {
					put_char('\b', tty);
					put_char(' ', tty);
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
				if (!iscntrl(c) || L_ECHOCTL(tty)) {
					put_char('\b', tty);
					put_char(' ', tty);
					put_char('\b', tty);
					if (tty->column > 0)
						tty->column--;
				}
			}
		}
		if (kill_type == ERASE)
			break;
	}
	if (tty->read_head == tty->canon_head)
		finish_erasing(tty);
}
/*
 * Perform OPOST processing.  Returns -1 when the output device is
 * full and the character must be retried.
 */
static int opost(unsigned char c, struct tty_struct *tty) 输出预处理
{
	int	space, spaces;

	space = tty->driver.write_room(tty); 取输出设备剩余缓冲区空间
	if (!space)
		return -1;

	if (O_OPOST(tty)) { 如果允许输出预处理
		switch (c) {
		case '\n':
			if (O_ONLRET(tty)) 换行时是否回车
				tty->column = 0; 
			if (O_ONLCR(tty)) {
				if (space < 2)
					return -1;
				tty->driver.put_char(tty, '\r');
				tty->column = 0;
			}
			tty->canon_column = tty->column;
			break;
		case '\r':
			if (O_ONOCR(tty) && tty->column == 0) 禁止重复输出回车符
				return 0;
			if (O_OCRNL(tty)) { 回车符转换为换行符
				c = '\n';
				if (O_ONLRET(tty))
					tty->canon_column = tty->column = 0;
				break;
			}
			tty->canon_column = tty->column = 0;
			break;
		case '\t':
			spaces = 8 - (tty->column & 7);
			if (O_TABDLY(tty) == XTABS) {
				if (space < spaces)
					return -1;
				tty->column += spaces;
				tty->driver.write(tty, 0, "        ", spaces); 
				return 0;
			}
			tty->column += spaces;
			break;
		case '\b':
			if (tty->column > 0)
				tty->column--; 退格
			break;
		default:
			if (O_OLCUC(tty)) 小写转换成大写
				c = toupper(c); 
			if (!iscntrl(c)) 如果不是控制符
				tty->column++;
			break;
		}
	}
	tty->driver.put_char(tty, c);
	return 0;
}

/*
 * Reset the read buffer counters, clear the flags, 
 * and make sure the driver is unthrottled. Called
 * from n_tty_open() and n_tty_flush_buffer().
 */
static void reset_buffer_flags(struct tty_struct *tty)
{
	unsigned long flags;

	spin_lock_irqsave(&tty->read_lock, flags);
	tty->read_head = tty->read_tail = tty->read_cnt = 0;
	spin_unlock_irqrestore(&tty->read_lock, flags);
	tty->canon_head = tty->canon_data = tty->erasing = 0;
	memset(&tty->read_flags, 0, sizeof tty->read_flags);
	check_unthrottle(tty);
}

static int n_tty_open(struct tty_struct *tty)
{
	if (!tty)
		return -EINVAL;

	if (!tty->read_buf) {
		tty->read_buf = alloc_buf();
		if (!tty->read_buf)
			return -ENOMEM;
	}
	memset(tty->read_buf, 0, N_TTY_BUF_SIZE);
	reset_buffer_flags(tty);
	tty->column = 0;
	n_tty_set_termios(tty, 0);
	tty->minimum_to_wake = 1;
	tty->closing = 0;
	return 0;
}

/*
 * This character is the same as _POSIX_VDISABLE: it cannot be used as
 * a c_cc[] character, but indicates that a particular special character
 * isn't in use (eg VINTR has no character etc)
 */
#define __DISABLED_CHAR '\0'

static void n_tty_set_termios(struct tty_struct *tty, struct termios * old)
{
	if (!tty)
		return;
	
	tty->icanon = (L_ICANON(tty) != 0);
	if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
		tty->raw = 1;
		tty->real_raw = 1;
		return;
	}
	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
	    I_PARMRK(tty)) {
		cli();
		memset(tty->process_char_map, 0, 256/8);

		if (I_IGNCR(tty) || I_ICRNL(tty))
			set_bit('\r', &tty->process_char_map);
		if (I_INLCR(tty))
			set_bit('\n', &tty->process_char_map);

		if (L_ICANON(tty)) {
			set_bit(ERASE_CHAR(tty), &tty->process_char_map);
			set_bit(KILL_CHAR(tty), &tty->process_char_map);
			set_bit(EOF_CHAR(tty), &tty->process_char_map);
			set_bit('\n', &tty->process_char_map);
			set_bit(EOL_CHAR(tty), &tty->process_char_map);
			if (L_IEXTEN(tty)) {
				set_bit(WERASE_CHAR(tty),
					&tty->process_char_map);
				set_bit(LNEXT_CHAR(tty),
					&tty->process_char_map);
				set_bit(EOL2_CHAR(tty),
					&tty->process_char_map);
				if (L_ECHO(tty))
					set_bit(REPRINT_CHAR(tty),
						&tty->process_char_map);
			}
		}
		if (I_IXON(tty)) {
			set_bit(START_CHAR(tty), &tty->process_char_map);
			set_bit(STOP_CHAR(tty), &tty->process_char_map);
		}
		if (L_ISIG(tty)) {
			set_bit(INTR_CHAR(tty), &tty->process_char_map);
			set_bit(QUIT_CHAR(tty), &tty->process_char_map);
			set_bit(SUSP_CHAR(tty), &tty->process_char_map);
		}
		clear_bit(__DISABLED_CHAR, &tty->process_char_map);
		sti();
		tty->raw = 0;
		tty->real_raw = 0;
	} else {
		tty->raw = 1;
		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
		    (tty->driver.flags & TTY_DRIVER_REAL_RAW))
			tty->real_raw = 1;
		else
			tty->real_raw = 0;
	}
}

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