diff options
Diffstat (limited to 'drivers/tty/n_tty.c')
| -rw-r--r-- | drivers/tty/n_tty.c | 2539 |
1 files changed, 2539 insertions, 0 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c new file mode 100644 index 000000000..4dff2f34e --- /dev/null +++ b/drivers/tty/n_tty.c @@ -0,0 +1,2539 @@ +// SPDX-License-Identifier: GPL-1.0+ +/* + * n_tty.c --- implements the N_TTY line discipline. + * + * This code used to be in tty_io.c, but things are getting hairy + * enough that it made sense to split things off. (The N_TTY + * processing has changed so much that it's hardly recognizable, + * anyway...) + * + * Note that the open routine for N_TTY is guaranteed never to return + * an error. This is because Linux will fall back to setting a line + * to N_TTY if it can not switch to any other line discipline. + * + * Written by Theodore Ts'o, Copyright 1994. + * + * This file also contains code originally written by Linus Torvalds, + * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994. + * + * Reduced memory usage for older ARM systems - Russell King. + * + * 2000/01/20 Fixed SMP locking on put_tty_queue using bits of + * the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu> + * who actually finally proved there really was a race. + * + * 2002/03/18 Implemented n_tty_wakeup to send SIGIO POLL_OUTs to + * waiting writing processes-Sapan Bhatia <sapan@corewars.org>. + * Also fixed a bug in BLOCKING mode where n_tty_write returns + * EAGAIN + */ + +#include <linux/types.h> +#include <linux/major.h> +#include <linux/errno.h> +#include <linux/signal.h> +#include <linux/fcntl.h> +#include <linux/sched.h> +#include <linux/interrupt.h> +#include <linux/tty.h> +#include <linux/timer.h> +#include <linux/ctype.h> +#include <linux/mm.h> +#include <linux/string.h> +#include <linux/slab.h> +#include <linux/poll.h> +#include <linux/bitops.h> +#include <linux/audit.h> +#include <linux/file.h> +#include <linux/uaccess.h> +#include <linux/module.h> +#include <linux/ratelimit.h> +#include <linux/vmalloc.h> +#include "tty.h" + +/* + * Until this number of characters is queued in the xmit buffer, select will + * return "we have room for writes". + */ +#define WAKEUP_CHARS 256 + +/* + * 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 + +/* + * Special byte codes used in the echo buffer to represent operations + * or special handling of characters. Bytes in the echo buffer that + * are not part of such special blocks are treated as normal character + * codes. + */ +#define ECHO_OP_START 0xff +#define ECHO_OP_MOVE_BACK_COL 0x80 +#define ECHO_OP_SET_CANON_COL 0x81 +#define ECHO_OP_ERASE_TAB 0x82 + +#define ECHO_COMMIT_WATERMARK 256 +#define ECHO_BLOCK 256 +#define ECHO_DISCARD_WATERMARK N_TTY_BUF_SIZE - (ECHO_BLOCK + 32) + + +#undef N_TTY_TRACE +#ifdef N_TTY_TRACE +# define n_tty_trace(f, args...) trace_printk(f, ##args) +#else +# define n_tty_trace(f, args...) no_printk(f, ##args) +#endif + +struct n_tty_data { + /* producer-published */ + size_t read_head; + size_t commit_head; + size_t canon_head; + size_t echo_head; + size_t echo_commit; + size_t echo_mark; + DECLARE_BITMAP(char_map, 256); + + /* private to n_tty_receive_overrun (single-threaded) */ + unsigned long overrun_time; + int num_overrun; + + /* non-atomic */ + bool no_room; + + /* must hold exclusive termios_rwsem to reset these */ + unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1; + unsigned char push:1; + + /* shared by producer and consumer */ + char read_buf[N_TTY_BUF_SIZE]; + DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE); + unsigned char echo_buf[N_TTY_BUF_SIZE]; + + /* consumer-published */ + size_t read_tail; + size_t line_start; + + /* # of chars looked ahead (to find software flow control chars) */ + size_t lookahead_count; + + /* protected by output lock */ + unsigned int column; + unsigned int canon_column; + size_t echo_tail; + + struct mutex atomic_read_lock; + struct mutex output_lock; +}; + +#define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1)) + +static inline size_t read_cnt(struct n_tty_data *ldata) +{ + return ldata->read_head - ldata->read_tail; +} + +static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i) +{ + return ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)]; +} + +static inline unsigned char *read_buf_addr(struct n_tty_data *ldata, size_t i) +{ + return &ldata->read_buf[i & (N_TTY_BUF_SIZE - 1)]; +} + +static inline unsigned char echo_buf(struct n_tty_data *ldata, size_t i) +{ + smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */ + return ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)]; +} + +static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i) +{ + return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)]; +} + +/* If we are not echoing the data, perhaps this is a secret so erase it */ +static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size) +{ + bool icanon = !!L_ICANON(tty); + bool no_echo = !L_ECHO(tty); + + if (icanon && no_echo) + memset(buffer, 0x00, size); +} + +static void tty_copy(struct tty_struct *tty, void *to, size_t tail, size_t n) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t size = N_TTY_BUF_SIZE - tail; + void *from = read_buf_addr(ldata, tail); + + if (n > size) { + tty_audit_add_data(tty, from, size); + memcpy(to, from, size); + zero_buffer(tty, from, size); + to += size; + n -= size; + from = ldata->read_buf; + } + + tty_audit_add_data(tty, from, n); + memcpy(to, from, n); + zero_buffer(tty, from, n); +} + +/** + * n_tty_kick_worker - start input worker (if required) + * @tty: terminal + * + * Re-schedules the flip buffer work if it may have stopped. + * + * Locking: + * * Caller holds exclusive %termios_rwsem, or + * * n_tty_read()/consumer path: + * holds non-exclusive %termios_rwsem + */ +static void n_tty_kick_worker(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + /* Did the input worker stop? Restart it */ + if (unlikely(READ_ONCE(ldata->no_room))) { + WRITE_ONCE(ldata->no_room, 0); + + WARN_RATELIMIT(tty->port->itty == NULL, + "scheduling with invalid itty\n"); + /* see if ldisc has been killed - if so, this means that + * even though the ldisc has been halted and ->buf.work + * cancelled, ->buf.work is about to be rescheduled + */ + WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags), + "scheduling buffer work for halted ldisc\n"); + tty_buffer_restart_work(tty->port); + } +} + +static ssize_t chars_in_buffer(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + ssize_t n = 0; + + if (!ldata->icanon) + n = ldata->commit_head - ldata->read_tail; + else + n = ldata->canon_head - ldata->read_tail; + return n; +} + +/** + * n_tty_write_wakeup - asynchronous I/O notifier + * @tty: tty device + * + * Required for the ptys, serial driver etc. since processes that attach + * themselves to the master and rely on ASYNC IO must be woken up. + */ +static void n_tty_write_wakeup(struct tty_struct *tty) +{ + clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); + kill_fasync(&tty->fasync, SIGIO, POLL_OUT); +} + +static void n_tty_check_throttle(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + /* + * 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 (ldata->icanon && ldata->canon_head == ldata->read_tail) + return; + + while (1) { + int throttled; + tty_set_flow_change(tty, TTY_THROTTLE_SAFE); + if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE) + break; + throttled = tty_throttle_safe(tty); + if (!throttled) + break; + } + __tty_set_flow_change(tty, 0); +} + +static void n_tty_check_unthrottle(struct tty_struct *tty) +{ + if (tty->driver->type == TTY_DRIVER_TYPE_PTY) { + if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE) + return; + n_tty_kick_worker(tty); + tty_wakeup(tty->link); + return; + } + + /* If there is enough space in the read buffer now, let the + * low-level driver know. We use 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. + */ + + while (1) { + int unthrottled; + tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE); + if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE) + break; + n_tty_kick_worker(tty); + unthrottled = tty_unthrottle_safe(tty); + if (!unthrottled) + break; + } + __tty_set_flow_change(tty, 0); +} + +/** + * put_tty_queue - add character to tty + * @c: character + * @ldata: n_tty data + * + * Add a character to the tty read_buf queue. + * + * Locking: + * * n_tty_receive_buf()/producer path: + * caller holds non-exclusive %termios_rwsem + */ +static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata) +{ + *read_buf_addr(ldata, ldata->read_head) = c; + ldata->read_head++; +} + +/** + * reset_buffer_flags - reset buffer state + * @ldata: line disc data to reset + * + * Reset the read buffer counters and clear the flags. Called from + * n_tty_open() and n_tty_flush_buffer(). + * + * Locking: + * * caller holds exclusive %termios_rwsem, or + * * (locking is not required) + */ +static void reset_buffer_flags(struct n_tty_data *ldata) +{ + ldata->read_head = ldata->canon_head = ldata->read_tail = 0; + ldata->commit_head = 0; + ldata->line_start = 0; + + ldata->erasing = 0; + bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE); + ldata->push = 0; + + ldata->lookahead_count = 0; +} + +static void n_tty_packet_mode_flush(struct tty_struct *tty) +{ + unsigned long flags; + + if (tty->link->ctrl.packet) { + spin_lock_irqsave(&tty->ctrl.lock, flags); + tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD; + spin_unlock_irqrestore(&tty->ctrl.lock, flags); + wake_up_interruptible(&tty->link->read_wait); + } +} + +/** + * n_tty_flush_buffer - clean input queue + * @tty: terminal device + * + * Flush the input buffer. Called when the tty layer wants the buffer flushed + * (eg at hangup) or when the %N_TTY line discipline internally has to clean + * the pending queue (for example some signals). + * + * Holds %termios_rwsem to exclude producer/consumer while buffer indices are + * reset. + * + * Locking: %ctrl.lock, exclusive %termios_rwsem + */ +static void n_tty_flush_buffer(struct tty_struct *tty) +{ + down_write(&tty->termios_rwsem); + reset_buffer_flags(tty->disc_data); + n_tty_kick_worker(tty); + + if (tty->link) + n_tty_packet_mode_flush(tty); + up_write(&tty->termios_rwsem); +} + +/** + * is_utf8_continuation - utf8 multibyte check + * @c: byte to check + * + * Returns: true if the utf8 character @c is a multibyte continuation + * character. We use this to correctly compute the on-screen size of the + * character when printing. + */ +static inline int is_utf8_continuation(unsigned char c) +{ + return (c & 0xc0) == 0x80; +} + +/** + * is_continuation - multibyte check + * @c: byte to check + * @tty: terminal device + * + * Returns: true if the utf8 character @c is a multibyte continuation character + * and the terminal is in unicode mode. + */ +static inline int is_continuation(unsigned char c, struct tty_struct *tty) +{ + return I_IUTF8(tty) && is_utf8_continuation(c); +} + +/** + * do_output_char - output one character + * @c: character (or partial unicode symbol) + * @tty: terminal device + * @space: space available in tty driver write buffer + * + * This is a helper function that handles one output character (including + * special characters like TAB, CR, LF, etc.), doing OPOST processing and + * putting the results in the tty driver's write buffer. + * + * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. + * They simply aren't relevant in the world today. If you ever need them, add + * them here. + * + * Returns: the number of bytes of buffer space used or -1 if no space left. + * + * Locking: should be called under the %output_lock to protect the column state + * and space left in the buffer. + */ +static int do_output_char(unsigned char c, struct tty_struct *tty, int space) +{ + struct n_tty_data *ldata = tty->disc_data; + int spaces; + + if (!space) + return -1; + + switch (c) { + case '\n': + if (O_ONLRET(tty)) + ldata->column = 0; + if (O_ONLCR(tty)) { + if (space < 2) + return -1; + ldata->canon_column = ldata->column = 0; + tty->ops->write(tty, "\r\n", 2); + return 2; + } + ldata->canon_column = ldata->column; + break; + case '\r': + if (O_ONOCR(tty) && ldata->column == 0) + return 0; + if (O_OCRNL(tty)) { + c = '\n'; + if (O_ONLRET(tty)) + ldata->canon_column = ldata->column = 0; + break; + } + ldata->canon_column = ldata->column = 0; + break; + case '\t': + spaces = 8 - (ldata->column & 7); + if (O_TABDLY(tty) == XTABS) { + if (space < spaces) + return -1; + ldata->column += spaces; + tty->ops->write(tty, " ", spaces); + return spaces; + } + ldata->column += spaces; + break; + case '\b': + if (ldata->column > 0) + ldata->column--; + break; + default: + if (!iscntrl(c)) { + if (O_OLCUC(tty)) + c = toupper(c); + if (!is_continuation(c, tty)) + ldata->column++; + } + break; + } + + tty_put_char(tty, c); + return 1; +} + +/** + * process_output - output post processor + * @c: character (or partial unicode symbol) + * @tty: terminal device + * + * Output one character with OPOST processing. + * + * Returns: -1 when the output device is full and the character must be + * retried. + * + * Locking: %output_lock to protect column state and space left (also, this is + *called from n_tty_write() under the tty layer write lock). + */ +static int process_output(unsigned char c, struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + int space, retval; + + mutex_lock(&ldata->output_lock); + + space = tty_write_room(tty); + retval = do_output_char(c, tty, space); + + mutex_unlock(&ldata->output_lock); + if (retval < 0) + return -1; + else + return 0; +} + +/** + * process_output_block - block post processor + * @tty: terminal device + * @buf: character buffer + * @nr: number of bytes to output + * + * Output a block of characters with OPOST processing. + * + * This path is used to speed up block console writes, among other things when + * processing blocks of output data. It handles only the simple cases normally + * found and helps to generate blocks of symbols for the console driver and + * thus improve performance. + * + * Returns: the number of characters output. + * + * Locking: %output_lock to protect column state and space left (also, this is + * called from n_tty_write() under the tty layer write lock). + */ +static ssize_t process_output_block(struct tty_struct *tty, + const unsigned char *buf, unsigned int nr) +{ + struct n_tty_data *ldata = tty->disc_data; + int space; + int i; + const unsigned char *cp; + + mutex_lock(&ldata->output_lock); + + space = tty_write_room(tty); + if (space <= 0) { + mutex_unlock(&ldata->output_lock); + return space; + } + if (nr > space) + nr = space; + + for (i = 0, cp = buf; i < nr; i++, cp++) { + unsigned char c = *cp; + + switch (c) { + case '\n': + if (O_ONLRET(tty)) + ldata->column = 0; + if (O_ONLCR(tty)) + goto break_out; + ldata->canon_column = ldata->column; + break; + case '\r': + if (O_ONOCR(tty) && ldata->column == 0) + goto break_out; + if (O_OCRNL(tty)) + goto break_out; + ldata->canon_column = ldata->column = 0; + break; + case '\t': + goto break_out; + case '\b': + if (ldata->column > 0) + ldata->column--; + break; + default: + if (!iscntrl(c)) { + if (O_OLCUC(tty)) + goto break_out; + if (!is_continuation(c, tty)) + ldata->column++; + } + break; + } + } +break_out: + i = tty->ops->write(tty, buf, i); + + mutex_unlock(&ldata->output_lock); + return i; +} + +/** + * __process_echoes - write pending echo characters + * @tty: terminal device + * + * Write previously buffered echo (and other ldisc-generated) characters to the + * tty. + * + * Characters generated by the ldisc (including echoes) need to be buffered + * because the driver's write buffer can fill during heavy program output. + * Echoing straight to the driver will often fail under these conditions, + * causing lost characters and resulting mismatches of ldisc state information. + * + * Since the ldisc state must represent the characters actually sent to the + * driver at the time of the write, operations like certain changes in column + * state are also saved in the buffer and executed here. + * + * A circular fifo buffer is used so that the most recent characters are + * prioritized. Also, when control characters are echoed with a prefixed "^", + * the pair is treated atomically and thus not separated. + * + * Locking: callers must hold %output_lock. + */ +static size_t __process_echoes(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + int space, old_space; + size_t tail; + unsigned char c; + + old_space = space = tty_write_room(tty); + + tail = ldata->echo_tail; + while (MASK(ldata->echo_commit) != MASK(tail)) { + c = echo_buf(ldata, tail); + if (c == ECHO_OP_START) { + unsigned char op; + int no_space_left = 0; + + /* + * Since add_echo_byte() is called without holding + * output_lock, we might see only portion of multi-byte + * operation. + */ + if (MASK(ldata->echo_commit) == MASK(tail + 1)) + goto not_yet_stored; + /* + * If the buffer byte is the start of a multi-byte + * operation, get the next byte, which is either the + * op code or a control character value. + */ + op = echo_buf(ldata, tail + 1); + + switch (op) { + case ECHO_OP_ERASE_TAB: { + unsigned int num_chars, num_bs; + + if (MASK(ldata->echo_commit) == MASK(tail + 2)) + goto not_yet_stored; + num_chars = echo_buf(ldata, tail + 2); + + /* + * Determine how many columns to go back + * in order to erase the tab. + * This depends on the number of columns + * used by other characters within the tab + * area. If this (modulo 8) count is from + * the start of input rather than from a + * previous tab, we offset by canon column. + * Otherwise, tab spacing is normal. + */ + if (!(num_chars & 0x80)) + num_chars += ldata->canon_column; + num_bs = 8 - (num_chars & 7); + + if (num_bs > space) { + no_space_left = 1; + break; + } + space -= num_bs; + while (num_bs--) { + tty_put_char(tty, '\b'); + if (ldata->column > 0) + ldata->column--; + } + tail += 3; + break; + } + case ECHO_OP_SET_CANON_COL: + ldata->canon_column = ldata->column; + tail += 2; + break; + + case ECHO_OP_MOVE_BACK_COL: + if (ldata->column > 0) + ldata->column--; + tail += 2; + break; + + case ECHO_OP_START: + /* This is an escaped echo op start code */ + if (!space) { + no_space_left = 1; + break; + } + tty_put_char(tty, ECHO_OP_START); + ldata->column++; + space--; + tail += 2; + break; + + default: + /* + * If the op is not a special byte code, + * it is a ctrl char tagged to be echoed + * as "^X" (where X is the letter + * representing the control char). + * Note that we must ensure there is + * enough space for the whole ctrl pair. + * + */ + if (space < 2) { + no_space_left = 1; + break; + } + tty_put_char(tty, '^'); + tty_put_char(tty, op ^ 0100); + ldata->column += 2; + space -= 2; + tail += 2; + } + + if (no_space_left) + break; + } else { + if (O_OPOST(tty)) { + int retval = do_output_char(c, tty, space); + if (retval < 0) + break; + space -= retval; + } else { + if (!space) + break; + tty_put_char(tty, c); + space -= 1; + } + tail += 1; + } + } + + /* If the echo buffer is nearly full (so that the possibility exists + * of echo overrun before the next commit), then discard enough + * data at the tail to prevent a subsequent overrun */ + while (ldata->echo_commit > tail && + ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) { + if (echo_buf(ldata, tail) == ECHO_OP_START) { + if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB) + tail += 3; + else + tail += 2; + } else + tail++; + } + + not_yet_stored: + ldata->echo_tail = tail; + return old_space - space; +} + +static void commit_echoes(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t nr, old, echoed; + size_t head; + + mutex_lock(&ldata->output_lock); + head = ldata->echo_head; + ldata->echo_mark = head; + old = ldata->echo_commit - ldata->echo_tail; + + /* Process committed echoes if the accumulated # of bytes + * is over the threshold (and try again each time another + * block is accumulated) */ + nr = head - ldata->echo_tail; + if (nr < ECHO_COMMIT_WATERMARK || + (nr % ECHO_BLOCK > old % ECHO_BLOCK)) { + mutex_unlock(&ldata->output_lock); + return; + } + + ldata->echo_commit = head; + echoed = __process_echoes(tty); + mutex_unlock(&ldata->output_lock); + + if (echoed && tty->ops->flush_chars) + tty->ops->flush_chars(tty); +} + +static void process_echoes(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t echoed; + + if (ldata->echo_mark == ldata->echo_tail) + return; + + mutex_lock(&ldata->output_lock); + ldata->echo_commit = ldata->echo_mark; + echoed = __process_echoes(tty); + mutex_unlock(&ldata->output_lock); + + if (echoed && tty->ops->flush_chars) + tty->ops->flush_chars(tty); +} + +/* NB: echo_mark and echo_head should be equivalent here */ +static void flush_echoes(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + if ((!L_ECHO(tty) && !L_ECHONL(tty)) || + ldata->echo_commit == ldata->echo_head) + return; + + mutex_lock(&ldata->output_lock); + ldata->echo_commit = ldata->echo_head; + __process_echoes(tty); + mutex_unlock(&ldata->output_lock); +} + +/** + * add_echo_byte - add a byte to the echo buffer + * @c: unicode byte to echo + * @ldata: n_tty data + * + * Add a character or operation byte to the echo buffer. + */ +static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata) +{ + *echo_buf_addr(ldata, ldata->echo_head) = c; + smp_wmb(); /* Matches smp_rmb() in echo_buf(). */ + ldata->echo_head++; +} + +/** + * echo_move_back_col - add operation to move back a column + * @ldata: n_tty data + * + * Add an operation to the echo buffer to move back one column. + */ +static void echo_move_back_col(struct n_tty_data *ldata) +{ + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata); +} + +/** + * echo_set_canon_col - add operation to set the canon column + * @ldata: n_tty data + * + * Add an operation to the echo buffer to set the canon column to the current + * column. + */ +static void echo_set_canon_col(struct n_tty_data *ldata) +{ + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(ECHO_OP_SET_CANON_COL, ldata); +} + +/** + * echo_erase_tab - add operation to erase a tab + * @num_chars: number of character columns already used + * @after_tab: true if num_chars starts after a previous tab + * @ldata: n_tty data + * + * Add an operation to the echo buffer to erase a tab. + * + * Called by the eraser function, which knows how many character columns have + * been used since either a previous tab or the start of input. This + * information will be used later, along with canon column (if applicable), to + * go back the correct number of columns. + */ +static void echo_erase_tab(unsigned int num_chars, int after_tab, + struct n_tty_data *ldata) +{ + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(ECHO_OP_ERASE_TAB, ldata); + + /* We only need to know this modulo 8 (tab spacing) */ + num_chars &= 7; + + /* Set the high bit as a flag if num_chars is after a previous tab */ + if (after_tab) + num_chars |= 0x80; + + add_echo_byte(num_chars, ldata); +} + +/** + * echo_char_raw - echo a character raw + * @c: unicode byte to echo + * @ldata: line disc data + * + * Echo user input back onto the screen. This must be called only when + * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path. + * + * This variant does not treat control characters specially. + */ +static void echo_char_raw(unsigned char c, struct n_tty_data *ldata) +{ + if (c == ECHO_OP_START) { + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(ECHO_OP_START, ldata); + } else { + add_echo_byte(c, ldata); + } +} + +/** + * echo_char - echo a character + * @c: unicode byte to echo + * @tty: terminal device + * + * Echo user input back onto the screen. This must be called only when + * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path. + * + * This variant tags control characters to be echoed as "^X" (where X is the + * letter representing the control char). + */ +static void echo_char(unsigned char c, struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (c == ECHO_OP_START) { + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(ECHO_OP_START, ldata); + } else { + if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t') + add_echo_byte(ECHO_OP_START, ldata); + add_echo_byte(c, ldata); + } +} + +/** + * finish_erasing - complete erase + * @ldata: n_tty data + */ +static inline void finish_erasing(struct n_tty_data *ldata) +{ + if (ldata->erasing) { + echo_char_raw('/', ldata); + ldata->erasing = 0; + } +} + +/** + * eraser - handle erase function + * @c: character input + * @tty: terminal device + * + * Perform erase and necessary output when an erase character is present in the + * stream from the driver layer. Handles the complexities of UTF-8 multibyte + * symbols. + * + * Locking: n_tty_receive_buf()/producer path: + * caller holds non-exclusive %termios_rwsem + */ +static void eraser(unsigned char c, struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + enum { ERASE, WERASE, KILL } kill_type; + size_t head; + size_t cnt; + int seen_alnums; + + if (ldata->read_head == ldata->canon_head) { + /* process_output('\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)) { + ldata->read_head = ldata->canon_head; + return; + } + if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) { + ldata->read_head = ldata->canon_head; + finish_erasing(ldata); + echo_char(KILL_CHAR(tty), tty); + /* Add a newline if ECHOK is on and ECHOKE is off. */ + if (L_ECHOK(tty)) + echo_char_raw('\n', ldata); + return; + } + kill_type = KILL; + } + + seen_alnums = 0; + while (MASK(ldata->read_head) != MASK(ldata->canon_head)) { + head = ldata->read_head; + + /* erase a single possibly multibyte character */ + do { + head--; + c = read_buf(ldata, head); + } while (is_continuation(c, tty) && + MASK(head) != MASK(ldata->canon_head)); + + /* do not partially erase */ + if (is_continuation(c, tty)) + break; + + if (kill_type == WERASE) { + /* Equivalent to BSD's ALTWERASE. */ + if (isalnum(c) || c == '_') + seen_alnums++; + else if (seen_alnums) + break; + } + cnt = ldata->read_head - head; + ldata->read_head = head; + if (L_ECHO(tty)) { + if (L_ECHOPRT(tty)) { + if (!ldata->erasing) { + echo_char_raw('\\', ldata); + ldata->erasing = 1; + } + /* if cnt > 1, output a multi-byte character */ + echo_char(c, tty); + while (--cnt > 0) { + head++; + echo_char_raw(read_buf(ldata, head), ldata); + echo_move_back_col(ldata); + } + } else if (kill_type == ERASE && !L_ECHOE(tty)) { + echo_char(ERASE_CHAR(tty), tty); + } else if (c == '\t') { + unsigned int num_chars = 0; + int after_tab = 0; + size_t tail = ldata->read_head; + + /* + * Count the columns used for characters + * since the start of input or after a + * previous tab. + * This info is used to go back the correct + * number of columns. + */ + while (MASK(tail) != MASK(ldata->canon_head)) { + tail--; + c = read_buf(ldata, tail); + if (c == '\t') { + after_tab = 1; + break; + } else if (iscntrl(c)) { + if (L_ECHOCTL(tty)) + num_chars += 2; + } else if (!is_continuation(c, tty)) { + num_chars++; + } + } + echo_erase_tab(num_chars, after_tab, ldata); + } else { + if (iscntrl(c) && L_ECHOCTL(tty)) { + echo_char_raw('\b', ldata); + echo_char_raw(' ', ldata); + echo_char_raw('\b', ldata); + } + if (!iscntrl(c) || L_ECHOCTL(tty)) { + echo_char_raw('\b', ldata); + echo_char_raw(' ', ldata); + echo_char_raw('\b', ldata); + } + } + } + if (kill_type == ERASE) + break; + } + if (ldata->read_head == ldata->canon_head && L_ECHO(tty)) + finish_erasing(ldata); +} + + +static void __isig(int sig, struct tty_struct *tty) +{ + struct pid *tty_pgrp = tty_get_pgrp(tty); + if (tty_pgrp) { + kill_pgrp(tty_pgrp, sig, 1); + put_pid(tty_pgrp); + } +} + +/** + * isig - handle the ISIG optio + * @sig: signal + * @tty: terminal + * + * Called when a signal is being sent due to terminal input. Called from the + * &tty_driver.receive_buf() path, so serialized. + * + * Performs input and output flush if !NOFLSH. In this context, the echo + * buffer is 'output'. The signal is processed first to alert any current + * readers or writers to discontinue and exit their i/o loops. + * + * Locking: %ctrl.lock + */ +static void isig(int sig, struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (L_NOFLSH(tty)) { + /* signal only */ + __isig(sig, tty); + + } else { /* signal and flush */ + up_read(&tty->termios_rwsem); + down_write(&tty->termios_rwsem); + + __isig(sig, tty); + + /* clear echo buffer */ + mutex_lock(&ldata->output_lock); + ldata->echo_head = ldata->echo_tail = 0; + ldata->echo_mark = ldata->echo_commit = 0; + mutex_unlock(&ldata->output_lock); + + /* clear output buffer */ + tty_driver_flush_buffer(tty); + + /* clear input buffer */ + reset_buffer_flags(tty->disc_data); + + /* notify pty master of flush */ + if (tty->link) + n_tty_packet_mode_flush(tty); + + up_write(&tty->termios_rwsem); + down_read(&tty->termios_rwsem); + } +} + +/** + * n_tty_receive_break - handle break + * @tty: terminal + * + * An RS232 break event has been hit in the incoming bitstream. This can cause + * a variety of events depending upon the termios settings. + * + * Locking: n_tty_receive_buf()/producer path: + * caller holds non-exclusive termios_rwsem + * + * Note: may get exclusive %termios_rwsem if flushing input buffer + */ +static void n_tty_receive_break(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (I_IGNBRK(tty)) + return; + if (I_BRKINT(tty)) { + isig(SIGINT, tty); + return; + } + if (I_PARMRK(tty)) { + put_tty_queue('\377', ldata); + put_tty_queue('\0', ldata); + } + put_tty_queue('\0', ldata); +} + +/** + * n_tty_receive_overrun - handle overrun reporting + * @tty: terminal + * + * Data arrived faster than we could process it. While the tty driver has + * flagged this the bits that were missed are gone forever. + * + * Called from the receive_buf path so single threaded. Does not need locking + * as num_overrun and overrun_time are function private. + */ +static void n_tty_receive_overrun(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + ldata->num_overrun++; + if (time_after(jiffies, ldata->overrun_time + HZ) || + time_after(ldata->overrun_time, jiffies)) { + tty_warn(tty, "%d input overrun(s)\n", ldata->num_overrun); + ldata->overrun_time = jiffies; + ldata->num_overrun = 0; + } +} + +/** + * n_tty_receive_parity_error - error notifier + * @tty: terminal device + * @c: character + * + * Process a parity error and queue the right data to indicate the error case + * if necessary. + * + * Locking: n_tty_receive_buf()/producer path: + * caller holds non-exclusive %termios_rwsem + */ +static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (I_INPCK(tty)) { + if (I_IGNPAR(tty)) + return; + if (I_PARMRK(tty)) { + put_tty_queue('\377', ldata); + put_tty_queue('\0', ldata); + put_tty_queue(c, ldata); + } else + put_tty_queue('\0', ldata); + } else + put_tty_queue(c, ldata); +} + +static void +n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c) +{ + isig(signal, tty); + if (I_IXON(tty)) + start_tty(tty); + if (L_ECHO(tty)) { + echo_char(c, tty); + commit_echoes(tty); + } else + process_echoes(tty); +} + +static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c) +{ + return c == START_CHAR(tty) || c == STOP_CHAR(tty); +} + +/** + * n_tty_receive_char_flow_ctrl - receive flow control chars + * @tty: terminal device + * @c: character + * @lookahead_done: lookahead has processed this character already + * + * Receive and process flow control character actions. + * + * In case lookahead for flow control chars already handled the character in + * advance to the normal receive, the actions are skipped during normal + * receive. + * + * Returns true if @c is consumed as flow-control character, the character + * must not be treated as normal character. + */ +static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c, + bool lookahead_done) +{ + if (!n_tty_is_char_flow_ctrl(tty, c)) + return false; + + if (lookahead_done) + return true; + + if (c == START_CHAR(tty)) { + start_tty(tty); + process_echoes(tty); + return true; + } + + /* STOP_CHAR */ + stop_tty(tty); + return true; +} + +static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c, + bool lookahead_done) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done)) + return; + + if (L_ISIG(tty)) { + if (c == INTR_CHAR(tty)) { + n_tty_receive_signal_char(tty, SIGINT, c); + return; + } else if (c == QUIT_CHAR(tty)) { + n_tty_receive_signal_char(tty, SIGQUIT, c); + return; + } else if (c == SUSP_CHAR(tty)) { + n_tty_receive_signal_char(tty, SIGTSTP, c); + return; + } + } + + if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) { + start_tty(tty); + process_echoes(tty); + } + + if (c == '\r') { + if (I_IGNCR(tty)) + return; + if (I_ICRNL(tty)) + c = '\n'; + } else if (c == '\n' && I_INLCR(tty)) + c = '\r'; + + if (ldata->icanon) { + if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) || + (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) { + eraser(c, tty); + commit_echoes(tty); + return; + } + if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) { + ldata->lnext = 1; + if (L_ECHO(tty)) { + finish_erasing(ldata); + if (L_ECHOCTL(tty)) { + echo_char_raw('^', ldata); + echo_char_raw('\b', ldata); + commit_echoes(tty); + } + } + return; + } + if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) { + size_t tail = ldata->canon_head; + + finish_erasing(ldata); + echo_char(c, tty); + echo_char_raw('\n', ldata); + while (MASK(tail) != MASK(ldata->read_head)) { + echo_char(read_buf(ldata, tail), tty); + tail++; + } + commit_echoes(tty); + return; + } + if (c == '\n') { + if (L_ECHO(tty) || L_ECHONL(tty)) { + echo_char_raw('\n', ldata); + commit_echoes(tty); + } + goto handle_newline; + } + if (c == EOF_CHAR(tty)) { + 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)) { + /* Record the column of first canon char. */ + if (ldata->canon_head == ldata->read_head) + echo_set_canon_col(ldata); + echo_char(c, tty); + commit_echoes(tty); + } + /* + * XXX does PARMRK doubling happen for + * EOL_CHAR and EOL2_CHAR? + */ + if (c == (unsigned char) '\377' && I_PARMRK(tty)) + put_tty_queue(c, ldata); + +handle_newline: + set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags); + put_tty_queue(c, ldata); + smp_store_release(&ldata->canon_head, ldata->read_head); + kill_fasync(&tty->fasync, SIGIO, POLL_IN); + wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM); + return; + } + } + + if (L_ECHO(tty)) { + finish_erasing(ldata); + if (c == '\n') + echo_char_raw('\n', ldata); + else { + /* Record the column of first canon char. */ + if (ldata->canon_head == ldata->read_head) + echo_set_canon_col(ldata); + echo_char(c, tty); + } + commit_echoes(tty); + } + + /* PARMRK doubling check */ + if (c == (unsigned char) '\377' && I_PARMRK(tty)) + put_tty_queue(c, ldata); + + put_tty_queue(c, ldata); +} + +/** + * n_tty_receive_char - perform processing + * @tty: terminal device + * @c: character + * + * Process an individual character of input received from the driver. This is + * serialized with respect to itself by the rules for the driver above. + * + * Locking: n_tty_receive_buf()/producer path: + * caller holds non-exclusive %termios_rwsem + * publishes canon_head if canonical mode is active + */ +static void n_tty_receive_char(struct tty_struct *tty, unsigned char c) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) { + start_tty(tty); + process_echoes(tty); + } + if (L_ECHO(tty)) { + finish_erasing(ldata); + /* Record the column of first canon char. */ + if (ldata->canon_head == ldata->read_head) + echo_set_canon_col(ldata); + echo_char(c, tty); + commit_echoes(tty); + } + /* PARMRK doubling check */ + if (c == (unsigned char) '\377' && I_PARMRK(tty)) + put_tty_queue(c, ldata); + put_tty_queue(c, ldata); +} + +static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c, + bool lookahead_done) +{ + if (I_ISTRIP(tty)) + c &= 0x7f; + if (I_IUCLC(tty) && L_IEXTEN(tty)) + c = tolower(c); + + if (I_IXON(tty)) { + if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) && + tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) && + c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && + c != SUSP_CHAR(tty)) { + start_tty(tty); + process_echoes(tty); + } + } +} + +static void +n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag) +{ + switch (flag) { + case TTY_BREAK: + n_tty_receive_break(tty); + break; + case TTY_PARITY: + case TTY_FRAME: + n_tty_receive_parity_error(tty, c); + break; + case TTY_OVERRUN: + n_tty_receive_overrun(tty); + break; + default: + tty_err(tty, "unknown flag %d\n", flag); + break; + } +} + +static void +n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag) +{ + struct n_tty_data *ldata = tty->disc_data; + + ldata->lnext = 0; + if (likely(flag == TTY_NORMAL)) { + if (I_ISTRIP(tty)) + c &= 0x7f; + if (I_IUCLC(tty) && L_IEXTEN(tty)) + c = tolower(c); + n_tty_receive_char(tty, c); + } else + n_tty_receive_char_flagged(tty, c, flag); +} + +/* Caller must ensure count > 0 */ +static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const unsigned char *cp, + const unsigned char *fp, unsigned int count) +{ + struct n_tty_data *ldata = tty->disc_data; + unsigned char flag = TTY_NORMAL; + + ldata->lookahead_count += count; + + if (!I_IXON(tty)) + return; + + while (count--) { + if (fp) + flag = *fp++; + if (likely(flag == TTY_NORMAL)) + n_tty_receive_char_flow_ctrl(tty, *cp, false); + cp++; + } +} + +static void +n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t n, head; + + head = ldata->read_head & (N_TTY_BUF_SIZE - 1); + n = min_t(size_t, count, N_TTY_BUF_SIZE - head); + memcpy(read_buf_addr(ldata, head), cp, n); + ldata->read_head += n; + cp += n; + count -= n; + + head = ldata->read_head & (N_TTY_BUF_SIZE - 1); + n = min_t(size_t, count, N_TTY_BUF_SIZE - head); + memcpy(read_buf_addr(ldata, head), cp, n); + ldata->read_head += n; +} + +static void +n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count) +{ + struct n_tty_data *ldata = tty->disc_data; + char flag = TTY_NORMAL; + + while (count--) { + if (fp) + flag = *fp++; + if (likely(flag == TTY_NORMAL)) + put_tty_queue(*cp++, ldata); + else + n_tty_receive_char_flagged(tty, *cp++, flag); + } +} + +static void +n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count, bool lookahead_done) +{ + char flag = TTY_NORMAL; + + while (count--) { + if (fp) + flag = *fp++; + if (likely(flag == TTY_NORMAL)) + n_tty_receive_char_closing(tty, *cp++, lookahead_done); + } +} + +static void n_tty_receive_buf_standard(struct tty_struct *tty, + const unsigned char *cp, const char *fp, int count, bool lookahead_done) +{ + struct n_tty_data *ldata = tty->disc_data; + char flag = TTY_NORMAL; + + while (count--) { + unsigned char c = *cp++; + + if (fp) + flag = *fp++; + + if (ldata->lnext) { + n_tty_receive_char_lnext(tty, c, flag); + continue; + } + + if (unlikely(flag != TTY_NORMAL)) { + n_tty_receive_char_flagged(tty, c, flag); + continue; + } + + if (I_ISTRIP(tty)) + c &= 0x7f; + if (I_IUCLC(tty) && L_IEXTEN(tty)) + c = tolower(c); + if (L_EXTPROC(tty)) { + put_tty_queue(c, ldata); + continue; + } + + if (test_bit(c, ldata->char_map)) + n_tty_receive_char_special(tty, c, lookahead_done); + else + n_tty_receive_char(tty, c); + } +} + +static void __receive_buf(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count) +{ + struct n_tty_data *ldata = tty->disc_data; + bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty)); + size_t la_count = min_t(size_t, ldata->lookahead_count, count); + + if (ldata->real_raw) + n_tty_receive_buf_real_raw(tty, cp, fp, count); + else if (ldata->raw || (L_EXTPROC(tty) && !preops)) + n_tty_receive_buf_raw(tty, cp, fp, count); + else if (tty->closing && !L_EXTPROC(tty)) { + if (la_count > 0) + n_tty_receive_buf_closing(tty, cp, fp, la_count, true); + if (count > la_count) + n_tty_receive_buf_closing(tty, cp, fp, count - la_count, false); + } else { + if (la_count > 0) + n_tty_receive_buf_standard(tty, cp, fp, la_count, true); + if (count > la_count) + n_tty_receive_buf_standard(tty, cp, fp, count - la_count, false); + + flush_echoes(tty); + if (tty->ops->flush_chars) + tty->ops->flush_chars(tty); + } + + ldata->lookahead_count -= la_count; + + if (ldata->icanon && !L_EXTPROC(tty)) + return; + + /* publish read_head to consumer */ + smp_store_release(&ldata->commit_head, ldata->read_head); + + if (read_cnt(ldata)) { + kill_fasync(&tty->fasync, SIGIO, POLL_IN); + wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM); + } +} + +/** + * n_tty_receive_buf_common - process input + * @tty: device to receive input + * @cp: input chars + * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL) + * @count: number of input chars in @cp + * @flow: enable flow control + * + * Called by the terminal driver when a block of characters has been received. + * This function must be called from soft contexts not from interrupt context. + * The driver is responsible for making calls one at a time and in order (or + * using flush_to_ldisc()). + * + * Returns: the # of input chars from @cp which were processed. + * + * In canonical mode, the maximum line length is 4096 chars (including the line + * termination char); lines longer than 4096 chars are truncated. After 4095 + * chars, input data is still processed but not stored. Overflow processing + * ensures the tty can always receive more input until at least one line can be + * read. + * + * In non-canonical mode, the read buffer will only accept 4095 chars; this + * provides the necessary space for a newline char if the input mode is + * switched to canonical. + * + * Note it is possible for the read buffer to _contain_ 4096 chars in + * non-canonical mode: the read buffer could already contain the maximum canon + * line of 4096 chars when the mode is switched to non-canonical. + * + * Locking: n_tty_receive_buf()/producer path: + * claims non-exclusive %termios_rwsem + * publishes commit_head or canon_head + */ +static int +n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count, int flow) +{ + struct n_tty_data *ldata = tty->disc_data; + int room, n, rcvd = 0, overflow; + + down_read(&tty->termios_rwsem); + + do { + /* + * When PARMRK is set, each input char may take up to 3 chars + * in the read buf; reduce the buffer space avail by 3x + * + * 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. + * + * paired with store in *_copy_from_read_buf() -- guarantees + * the consumer has loaded the data in read_buf up to the new + * read_tail (so this producer will not overwrite unread data) + */ + size_t tail = smp_load_acquire(&ldata->read_tail); + + room = N_TTY_BUF_SIZE - (ldata->read_head - tail); + if (I_PARMRK(tty)) + room = (room + 2) / 3; + room--; + if (room <= 0) { + overflow = ldata->icanon && ldata->canon_head == tail; + if (overflow && room < 0) + ldata->read_head--; + room = overflow; + WRITE_ONCE(ldata->no_room, flow && !room); + } else + overflow = 0; + + n = min(count, room); + if (!n) + break; + + /* ignore parity errors if handling overflow */ + if (!overflow || !fp || *fp != TTY_PARITY) + __receive_buf(tty, cp, fp, n); + + cp += n; + if (fp) + fp += n; + count -= n; + rcvd += n; + } while (!test_bit(TTY_LDISC_CHANGING, &tty->flags)); + + tty->receive_room = room; + + /* Unthrottle if handling overflow on pty */ + if (tty->driver->type == TTY_DRIVER_TYPE_PTY) { + if (overflow) { + tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE); + tty_unthrottle_safe(tty); + __tty_set_flow_change(tty, 0); + } + } else + n_tty_check_throttle(tty); + + if (unlikely(ldata->no_room)) { + /* + * Barrier here is to ensure to read the latest read_tail in + * chars_in_buffer() and to make sure that read_tail is not loaded + * before ldata->no_room is set. + */ + smp_mb(); + if (!chars_in_buffer(tty)) + n_tty_kick_worker(tty); + } + + up_read(&tty->termios_rwsem); + + return rcvd; +} + +static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count) +{ + n_tty_receive_buf_common(tty, cp, fp, count, 0); +} + +static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp, + const char *fp, int count) +{ + return n_tty_receive_buf_common(tty, cp, fp, count, 1); +} + +/** + * n_tty_set_termios - termios data changed + * @tty: terminal + * @old: previous data + * + * Called by the tty layer when the user changes termios flags so that the line + * discipline can plan ahead. This function cannot sleep and is protected from + * re-entry by the tty layer. The user is guaranteed that this function will + * not be re-entered or in progress when the ldisc is closed. + * + * Locking: Caller holds @tty->termios_rwsem + */ +static void n_tty_set_termios(struct tty_struct *tty, const struct ktermios *old) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) { + bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE); + ldata->line_start = ldata->read_tail; + if (!L_ICANON(tty) || !read_cnt(ldata)) { + ldata->canon_head = ldata->read_tail; + ldata->push = 0; + } else { + set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1), + ldata->read_flags); + ldata->canon_head = ldata->read_head; + ldata->push = 1; + } + ldata->commit_head = ldata->read_head; + ldata->erasing = 0; + ldata->lnext = 0; + } + + ldata->icanon = (L_ICANON(tty) != 0); + + 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)) { + bitmap_zero(ldata->char_map, 256); + + if (I_IGNCR(tty) || I_ICRNL(tty)) + set_bit('\r', ldata->char_map); + if (I_INLCR(tty)) + set_bit('\n', ldata->char_map); + + if (L_ICANON(tty)) { + set_bit(ERASE_CHAR(tty), ldata->char_map); + set_bit(KILL_CHAR(tty), ldata->char_map); + set_bit(EOF_CHAR(tty), ldata->char_map); + set_bit('\n', ldata->char_map); + set_bit(EOL_CHAR(tty), ldata->char_map); + if (L_IEXTEN(tty)) { + set_bit(WERASE_CHAR(tty), ldata->char_map); + set_bit(LNEXT_CHAR(tty), ldata->char_map); + set_bit(EOL2_CHAR(tty), ldata->char_map); + if (L_ECHO(tty)) + set_bit(REPRINT_CHAR(tty), + ldata->char_map); + } + } + if (I_IXON(tty)) { + set_bit(START_CHAR(tty), ldata->char_map); + set_bit(STOP_CHAR(tty), ldata->char_map); + } + if (L_ISIG(tty)) { + set_bit(INTR_CHAR(tty), ldata->char_map); + set_bit(QUIT_CHAR(tty), ldata->char_map); + set_bit(SUSP_CHAR(tty), ldata->char_map); + } + clear_bit(__DISABLED_CHAR, ldata->char_map); + ldata->raw = 0; + ldata->real_raw = 0; + } else { + ldata->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)) + ldata->real_raw = 1; + else + ldata->real_raw = 0; + } + /* + * Fix tty hang when I_IXON(tty) is cleared, but the tty + * been stopped by STOP_CHAR(tty) before it. + */ + if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) { + start_tty(tty); + process_echoes(tty); + } + + /* The termios change make the tty ready for I/O */ + wake_up_interruptible(&tty->write_wait); + wake_up_interruptible(&tty->read_wait); +} + +/** + * n_tty_close - close the ldisc for this tty + * @tty: device + * + * Called from the terminal layer when this line discipline is being shut down, + * either because of a close or becsuse of a discipline change. The function + * will not be called while other ldisc methods are in progress. + */ +static void n_tty_close(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + if (tty->link) + n_tty_packet_mode_flush(tty); + + down_write(&tty->termios_rwsem); + vfree(ldata); + tty->disc_data = NULL; + up_write(&tty->termios_rwsem); +} + +/** + * n_tty_open - open an ldisc + * @tty: terminal to open + * + * Called when this line discipline is being attached to the terminal device. + * Can sleep. Called serialized so that no other events will occur in parallel. + * No further open will occur until a close. + */ +static int n_tty_open(struct tty_struct *tty) +{ + struct n_tty_data *ldata; + + /* Currently a malloc failure here can panic */ + ldata = vzalloc(sizeof(*ldata)); + if (!ldata) + return -ENOMEM; + + ldata->overrun_time = jiffies; + mutex_init(&ldata->atomic_read_lock); + mutex_init(&ldata->output_lock); + + tty->disc_data = ldata; + tty->closing = 0; + /* indicate buffer work may resume */ + clear_bit(TTY_LDISC_HALTED, &tty->flags); + n_tty_set_termios(tty, NULL); + tty_unthrottle(tty); + return 0; +} + +static inline int input_available_p(struct tty_struct *tty, int poll) +{ + struct n_tty_data *ldata = tty->disc_data; + int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1; + + if (ldata->icanon && !L_EXTPROC(tty)) + return ldata->canon_head != ldata->read_tail; + else + return ldata->commit_head - ldata->read_tail >= amt; +} + +/** + * copy_from_read_buf - copy read data directly + * @tty: terminal device + * @kbp: data + * @nr: size of data + * + * Helper function to speed up n_tty_read(). It is only called when %ICANON is + * off; it copies characters straight from the tty queue. + * + * Returns: true if it successfully copied data, but there is still more data + * to be had. + * + * Locking: + * * called under the @ldata->atomic_read_lock sem + * * n_tty_read()/consumer path: + * caller holds non-exclusive %termios_rwsem; + * read_tail published + */ +static bool copy_from_read_buf(struct tty_struct *tty, + unsigned char **kbp, + size_t *nr) + +{ + struct n_tty_data *ldata = tty->disc_data; + size_t n; + bool is_eof; + size_t head = smp_load_acquire(&ldata->commit_head); + size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1); + + n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail); + n = min(*nr, n); + if (n) { + unsigned char *from = read_buf_addr(ldata, tail); + memcpy(*kbp, from, n); + is_eof = n == 1 && *from == EOF_CHAR(tty); + tty_audit_add_data(tty, from, n); + zero_buffer(tty, from, n); + smp_store_release(&ldata->read_tail, ldata->read_tail + n); + /* Turn single EOF into zero-length read */ + if (L_EXTPROC(tty) && ldata->icanon && is_eof && + (head == ldata->read_tail)) + return false; + *kbp += n; + *nr -= n; + + /* If we have more to copy, let the caller know */ + return head != ldata->read_tail; + } + return false; +} + +/** + * canon_copy_from_read_buf - copy read data in canonical mode + * @tty: terminal device + * @kbp: data + * @nr: size of data + * + * Helper function for n_tty_read(). It is only called when %ICANON is on; it + * copies one line of input up to and including the line-delimiting character + * into the result buffer. + * + * Note: When termios is changed from non-canonical to canonical mode and the + * read buffer contains data, n_tty_set_termios() simulates an EOF push (as if + * C-d were input) _without_ the %DISABLED_CHAR in the buffer. This causes data + * already processed as input to be immediately available as input although a + * newline has not been received. + * + * Locking: + * * called under the %atomic_read_lock mutex + * * n_tty_read()/consumer path: + * caller holds non-exclusive %termios_rwsem; + * read_tail published + */ +static bool canon_copy_from_read_buf(struct tty_struct *tty, + unsigned char **kbp, + size_t *nr) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t n, size, more, c; + size_t eol; + size_t tail, canon_head; + int found = 0; + + /* N.B. avoid overrun if nr == 0 */ + if (!*nr) + return false; + + canon_head = smp_load_acquire(&ldata->canon_head); + n = min(*nr, canon_head - ldata->read_tail); + + tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1); + size = min_t(size_t, tail + n, N_TTY_BUF_SIZE); + + n_tty_trace("%s: nr:%zu tail:%zu n:%zu size:%zu\n", + __func__, *nr, tail, n, size); + + eol = find_next_bit(ldata->read_flags, size, tail); + more = n - (size - tail); + if (eol == N_TTY_BUF_SIZE && more) { + /* scan wrapped without finding set bit */ + eol = find_first_bit(ldata->read_flags, more); + found = eol != more; + } else + found = eol != size; + + n = eol - tail; + if (n > N_TTY_BUF_SIZE) + n += N_TTY_BUF_SIZE; + c = n + found; + + if (!found || read_buf(ldata, eol) != __DISABLED_CHAR) + n = c; + + n_tty_trace("%s: eol:%zu found:%d n:%zu c:%zu tail:%zu more:%zu\n", + __func__, eol, found, n, c, tail, more); + + tty_copy(tty, *kbp, tail, n); + *kbp += n; + *nr -= n; + + if (found) + clear_bit(eol, ldata->read_flags); + smp_store_release(&ldata->read_tail, ldata->read_tail + c); + + if (found) { + if (!ldata->push) + ldata->line_start = ldata->read_tail; + else + ldata->push = 0; + tty_audit_push(); + return false; + } + + /* No EOL found - do a continuation retry if there is more data */ + return ldata->read_tail != canon_head; +} + +/* + * If we finished a read at the exact location of an + * EOF (special EOL character that's a __DISABLED_CHAR) + * in the stream, silently eat the EOF. + */ +static void canon_skip_eof(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + size_t tail, canon_head; + + canon_head = smp_load_acquire(&ldata->canon_head); + tail = ldata->read_tail; + + // No data? + if (tail == canon_head) + return; + + // See if the tail position is EOF in the circular buffer + tail &= (N_TTY_BUF_SIZE - 1); + if (!test_bit(tail, ldata->read_flags)) + return; + if (read_buf(ldata, tail) != __DISABLED_CHAR) + return; + + // Clear the EOL bit, skip the EOF char. + clear_bit(tail, ldata->read_flags); + smp_store_release(&ldata->read_tail, ldata->read_tail + 1); +} + +/** + * job_control - check job control + * @tty: tty + * @file: file handle + * + * Perform job control management checks on this @file/@tty descriptor and if + * appropriate send any needed signals and return a negative error code if + * action should be taken. + * + * Locking: + * * redirected write test is safe + * * current->signal->tty check is safe + * * ctrl.lock to safely reference @tty->ctrl.pgrp + */ +static int job_control(struct tty_struct *tty, struct file *file) +{ + /* 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_op->write_iter == redirected_tty_write) + return 0; + + return __tty_check_change(tty, SIGTTIN); +} + + +/** + * n_tty_read - read function for tty + * @tty: tty device + * @file: file object + * @kbuf: kernelspace buffer pointer + * @nr: size of I/O + * @cookie: if non-%NULL, this is a continuation read + * @offset: where to continue reading from (unused in n_tty) + * + * Perform reads for the line discipline. We are guaranteed that the line + * discipline will not be closed under us but we may get multiple parallel + * readers and must handle this ourselves. We may also get a hangup. Always + * called in user context, may sleep. + * + * This code must be sure never to sleep through a hangup. + * + * Locking: n_tty_read()/consumer path: + * claims non-exclusive termios_rwsem; + * publishes read_tail + */ +static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, + unsigned char *kbuf, size_t nr, + void **cookie, unsigned long offset) +{ + struct n_tty_data *ldata = tty->disc_data; + unsigned char *kb = kbuf; + DEFINE_WAIT_FUNC(wait, woken_wake_function); + int c; + int minimum, time; + ssize_t retval = 0; + long timeout; + bool packet; + size_t old_tail; + + /* + * Is this a continuation of a read started earler? + * + * If so, we still hold the atomic_read_lock and the + * termios_rwsem, and can just continue to copy data. + */ + if (*cookie) { + if (ldata->icanon && !L_EXTPROC(tty)) { + /* + * If we have filled the user buffer, see + * if we should skip an EOF character before + * releasing the lock and returning done. + */ + if (!nr) + canon_skip_eof(tty); + else if (canon_copy_from_read_buf(tty, &kb, &nr)) + return kb - kbuf; + } else { + if (copy_from_read_buf(tty, &kb, &nr)) + return kb - kbuf; + } + + /* No more data - release locks and stop retries */ + n_tty_kick_worker(tty); + n_tty_check_unthrottle(tty); + up_read(&tty->termios_rwsem); + mutex_unlock(&ldata->atomic_read_lock); + *cookie = NULL; + return kb - kbuf; + } + + c = job_control(tty, file); + if (c < 0) + return c; + + /* + * Internal serialization of reads. + */ + if (file->f_flags & O_NONBLOCK) { + if (!mutex_trylock(&ldata->atomic_read_lock)) + return -EAGAIN; + } else { + if (mutex_lock_interruptible(&ldata->atomic_read_lock)) + return -ERESTARTSYS; + } + + down_read(&tty->termios_rwsem); + + minimum = time = 0; + timeout = MAX_SCHEDULE_TIMEOUT; + if (!ldata->icanon) { + minimum = MIN_CHAR(tty); + if (minimum) { + time = (HZ / 10) * TIME_CHAR(tty); + } else { + timeout = (HZ / 10) * TIME_CHAR(tty); + minimum = 1; + } + } + + packet = tty->ctrl.packet; + old_tail = ldata->read_tail; + + add_wait_queue(&tty->read_wait, &wait); + while (nr) { + /* First test for status change. */ + if (packet && tty->link->ctrl.pktstatus) { + unsigned char cs; + if (kb != kbuf) + break; + spin_lock_irq(&tty->link->ctrl.lock); + cs = tty->link->ctrl.pktstatus; + tty->link->ctrl.pktstatus = 0; + spin_unlock_irq(&tty->link->ctrl.lock); + *kb++ = cs; + nr--; + break; + } + + if (!input_available_p(tty, 0)) { + up_read(&tty->termios_rwsem); + tty_buffer_flush_work(tty->port); + down_read(&tty->termios_rwsem); + if (!input_available_p(tty, 0)) { + if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) { + retval = -EIO; + break; + } + if (tty_hung_up_p(file)) + break; + /* + * Abort readers for ttys which never actually + * get hung up. See __tty_hangup(). + */ + if (test_bit(TTY_HUPPING, &tty->flags)) + break; + if (!timeout) + break; + if (tty_io_nonblock(tty, file)) { + retval = -EAGAIN; + break; + } + if (signal_pending(current)) { + retval = -ERESTARTSYS; + break; + } + up_read(&tty->termios_rwsem); + + timeout = wait_woken(&wait, TASK_INTERRUPTIBLE, + timeout); + + down_read(&tty->termios_rwsem); + continue; + } + } + + if (ldata->icanon && !L_EXTPROC(tty)) { + if (canon_copy_from_read_buf(tty, &kb, &nr)) + goto more_to_be_read; + } else { + /* Deal with packet mode. */ + if (packet && kb == kbuf) { + *kb++ = TIOCPKT_DATA; + nr--; + } + + /* + * Copy data, and if there is more to be had + * and we have nothing more to wait for, then + * let's mark us for retries. + * + * NOTE! We return here with both the termios_sem + * and atomic_read_lock still held, the retries + * will release them when done. + */ + if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) { +more_to_be_read: + remove_wait_queue(&tty->read_wait, &wait); + *cookie = cookie; + return kb - kbuf; + } + } + + n_tty_check_unthrottle(tty); + + if (kb - kbuf >= minimum) + break; + if (time) + timeout = time; + } + if (old_tail != ldata->read_tail) { + /* + * Make sure no_room is not read in n_tty_kick_worker() + * before setting ldata->read_tail in copy_from_read_buf(). + */ + smp_mb(); + n_tty_kick_worker(tty); + } + up_read(&tty->termios_rwsem); + + remove_wait_queue(&tty->read_wait, &wait); + mutex_unlock(&ldata->atomic_read_lock); + + if (kb - kbuf) + retval = kb - kbuf; + + return retval; +} + +/** + * n_tty_write - write function for tty + * @tty: tty device + * @file: file object + * @buf: userspace buffer pointer + * @nr: size of I/O + * + * Write function of the terminal device. This is serialized with respect to + * other write callers but not to termios changes, reads and other such events. + * Since the receive code will echo characters, thus calling driver write + * methods, the %output_lock is used in the output processing functions called + * here as well as in the echo processing function to protect the column state + * and space left in the buffer. + * + * This code must be sure never to sleep through a hangup. + * + * Locking: output_lock to protect column state and space left + * (note that the process_output*() functions take this lock themselves) + */ + +static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, + const unsigned char *buf, size_t nr) +{ + const unsigned char *b = buf; + DEFINE_WAIT_FUNC(wait, woken_wake_function); + int c; + ssize_t retval = 0; + + /* Job control check -- must be done at start (POSIX.1 7.1.1.4). */ + if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) { + retval = tty_check_change(tty); + if (retval) + return retval; + } + + down_read(&tty->termios_rwsem); + + /* Write out any echoed characters that are still pending */ + process_echoes(tty); + + add_wait_queue(&tty->write_wait, &wait); + while (1) { + if (signal_pending(current)) { + retval = -ERESTARTSYS; + break; + } + if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) { + retval = -EIO; + break; + } + if (O_OPOST(tty)) { + while (nr > 0) { + ssize_t num = process_output_block(tty, b, nr); + if (num < 0) { + if (num == -EAGAIN) + break; + retval = num; + goto break_out; + } + b += num; + nr -= num; + if (nr == 0) + break; + c = *b; + if (process_output(c, tty) < 0) + break; + b++; nr--; + } + if (tty->ops->flush_chars) + tty->ops->flush_chars(tty); + } else { + struct n_tty_data *ldata = tty->disc_data; + + while (nr > 0) { + mutex_lock(&ldata->output_lock); + c = tty->ops->write(tty, b, nr); + mutex_unlock(&ldata->output_lock); + if (c < 0) { + retval = c; + goto break_out; + } + if (!c) + break; + b += c; + nr -= c; + } + } + if (!nr) + break; + if (tty_io_nonblock(tty, file)) { + retval = -EAGAIN; + break; + } + up_read(&tty->termios_rwsem); + + wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); + + down_read(&tty->termios_rwsem); + } +break_out: + remove_wait_queue(&tty->write_wait, &wait); + if (nr && tty->fasync) + set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); + up_read(&tty->termios_rwsem); + return (b - buf) ? b - buf : retval; +} + +/** + * n_tty_poll - poll method for N_TTY + * @tty: terminal device + * @file: file accessing it + * @wait: poll table + * + * Called when the line discipline is asked to poll() for data or for special + * events. This code is not serialized with respect to other events save + * open/close. + * + * This code must be sure never to sleep through a hangup. + * + * Locking: called without the kernel lock held -- fine. + */ +static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file, + poll_table *wait) +{ + __poll_t mask = 0; + + poll_wait(file, &tty->read_wait, wait); + poll_wait(file, &tty->write_wait, wait); + if (input_available_p(tty, 1)) + mask |= EPOLLIN | EPOLLRDNORM; + else { + tty_buffer_flush_work(tty->port); + if (input_available_p(tty, 1)) + mask |= EPOLLIN | EPOLLRDNORM; + } + if (tty->ctrl.packet && tty->link->ctrl.pktstatus) + mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM; + if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) + mask |= EPOLLHUP; + if (tty_hung_up_p(file)) + mask |= EPOLLHUP; + if (tty->ops->write && !tty_is_writelocked(tty) && + tty_chars_in_buffer(tty) < WAKEUP_CHARS && + tty_write_room(tty) > 0) + mask |= EPOLLOUT | EPOLLWRNORM; + return mask; +} + +static unsigned long inq_canon(struct n_tty_data *ldata) +{ + size_t nr, head, tail; + + if (ldata->canon_head == ldata->read_tail) + return 0; + head = ldata->canon_head; + tail = ldata->read_tail; + nr = head - tail; + /* Skip EOF-chars.. */ + while (MASK(head) != MASK(tail)) { + if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) && + read_buf(ldata, tail) == __DISABLED_CHAR) + nr--; + tail++; + } + return nr; +} + +static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd, + unsigned long arg) +{ + struct n_tty_data *ldata = tty->disc_data; + int retval; + + switch (cmd) { + case TIOCOUTQ: + return put_user(tty_chars_in_buffer(tty), (int __user *) arg); + case TIOCINQ: + down_write(&tty->termios_rwsem); + if (L_ICANON(tty) && !L_EXTPROC(tty)) + retval = inq_canon(ldata); + else + retval = read_cnt(ldata); + up_write(&tty->termios_rwsem); + return put_user(retval, (unsigned int __user *) arg); + default: + return n_tty_ioctl_helper(tty, cmd, arg); + } +} + +static struct tty_ldisc_ops n_tty_ops = { + .owner = THIS_MODULE, + .num = N_TTY, + .name = "n_tty", + .open = n_tty_open, + .close = n_tty_close, + .flush_buffer = n_tty_flush_buffer, + .read = n_tty_read, + .write = n_tty_write, + .ioctl = n_tty_ioctl, + .set_termios = n_tty_set_termios, + .poll = n_tty_poll, + .receive_buf = n_tty_receive_buf, + .write_wakeup = n_tty_write_wakeup, + .receive_buf2 = n_tty_receive_buf2, + .lookahead_buf = n_tty_lookahead_flow_ctrl, +}; + +/** + * n_tty_inherit_ops - inherit N_TTY methods + * @ops: struct tty_ldisc_ops where to save N_TTY methods + * + * Enables a 'subclass' line discipline to 'inherit' N_TTY methods. + */ + +void n_tty_inherit_ops(struct tty_ldisc_ops *ops) +{ + *ops = n_tty_ops; + ops->owner = NULL; +} +EXPORT_SYMBOL_GPL(n_tty_inherit_ops); + +void __init n_tty_init(void) +{ + tty_register_ldisc(&n_tty_ops); +} |