// 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 <[email protected]> * 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 <[email protected]>. * Also fixed a bug in BLOCKING mode where n_tty_write returns * EAGAIN */ #include <linux/bitmap.h> #include <linux/bitops.h> #include <linux/ctype.h> #include <linux/errno.h> #include <linux/export.h> #include <linux/fcntl.h> #include <linux/file.h> #include <linux/jiffies.h> #include <linux/math.h> #include <linux/poll.h> #include <linux/ratelimit.h> #include <linux/sched.h> #include <linux/signal.h> #include <linux/slab.h> #include <linux/string.h> #include <linux/tty.h> #include <linux/types.h> #include <linux/uaccess.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 … /* * 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 … #define TTY_THRESHOLD_UNTHROTTLE … /* * 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 … #define ECHO_OP_MOVE_BACK_COL … #define ECHO_OP_SET_CANON_COL … #define ECHO_OP_ERASE_TAB … #define ECHO_COMMIT_WATERMARK … #define ECHO_BLOCK … #define ECHO_DISCARD_WATERMARK … #undef N_TTY_TRACE #ifdef N_TTY_TRACE #define n_tty_trace … #else #define n_tty_trace(f, args...) … #endif struct n_tty_data { … }; #define MASK(x) … static inline size_t read_cnt(struct n_tty_data *ldata) { … } static inline u8 read_buf(struct n_tty_data *ldata, size_t i) { … } static inline u8 *read_buf_addr(struct n_tty_data *ldata, size_t i) { … } static inline u8 echo_buf(struct n_tty_data *ldata, size_t i) { … } static inline u8 *echo_buf_addr(struct n_tty_data *ldata, size_t i) { … } /* If we are not echoing the data, perhaps this is a secret so erase it */ static void zero_buffer(const struct tty_struct *tty, u8 *buffer, size_t size) { … } static void tty_copy(const struct tty_struct *tty, void *to, size_t tail, size_t 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(const struct tty_struct *tty) { … } static ssize_t chars_in_buffer(const struct tty_struct *tty) { … } /** * 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) { … } static void n_tty_check_throttle(struct tty_struct *tty) { … } static void n_tty_check_unthrottle(struct tty_struct *tty) { … } /** * 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(u8 c, struct n_tty_data *ldata) { … } /** * 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) { … } static void n_tty_packet_mode_flush(struct tty_struct *tty) { … } /** * 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) { … } /** * 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(u8 c) { … } /** * 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(u8 c, const struct tty_struct *tty) { … } /** * 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(u8 c, struct tty_struct *tty, int space) { … } /** * 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(u8 c, struct tty_struct *tty) { … } /** * 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 u8 *buf, unsigned int nr) { … } static int n_tty_process_echo_ops(struct tty_struct *tty, size_t *tail, int space) { … } /** * __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) { … } static void commit_echoes(struct tty_struct *tty) { … } static void process_echoes(struct tty_struct *tty) { … } /* NB: echo_mark and echo_head should be equivalent here */ static void flush_echoes(struct tty_struct *tty) { … } /** * 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(u8 c, struct n_tty_data *ldata) { … } /** * 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) { … } /** * 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) { … } /** * 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) { … } /** * 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(u8 c, struct n_tty_data *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(u8 c, const struct tty_struct *tty) { … } /** * finish_erasing - complete erase * @ldata: n_tty data */ static inline void finish_erasing(struct n_tty_data *ldata) { … } /** * 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(u8 c, const struct tty_struct *tty) { … } static void __isig(int sig, struct tty_struct *tty) { … } /** * 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) { … } /** * 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) { … } /** * 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(const struct tty_struct *tty) { … } /** * 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(const struct tty_struct *tty, u8 c) { … } static void n_tty_receive_signal_char(struct tty_struct *tty, int signal, u8 c) { … } static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, u8 c) { … } /** * 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, u8 c, bool lookahead_done) { … } static void n_tty_receive_handle_newline(struct tty_struct *tty, u8 c) { … } static bool n_tty_receive_char_canon(struct tty_struct *tty, u8 c) { … } static void n_tty_receive_char_special(struct tty_struct *tty, u8 c, bool lookahead_done) { … } /** * 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, u8 c) { … } static void n_tty_receive_char_closing(struct tty_struct *tty, u8 c, bool lookahead_done) { … } static void n_tty_receive_char_flagged(struct tty_struct *tty, u8 c, u8 flag) { … } static void n_tty_receive_char_lnext(struct tty_struct *tty, u8 c, u8 flag) { … } /* Caller must ensure count > 0 */ static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count) { … } static void n_tty_receive_buf_real_raw(const struct tty_struct *tty, const u8 *cp, size_t count) { … } static void n_tty_receive_buf_raw(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count) { … } static void n_tty_receive_buf_closing(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count, bool lookahead_done) { … } static void n_tty_receive_buf_standard(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count, bool lookahead_done) { … } static void __receive_buf(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count) { … } /** * 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 size_t n_tty_receive_buf_common(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count, bool flow) { … } static void n_tty_receive_buf(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count) { … } static size_t n_tty_receive_buf2(struct tty_struct *tty, const u8 *cp, const u8 *fp, size_t count) { … } /** * 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) { … } /** * 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) { … } /** * 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) { … } static inline int input_available_p(const struct tty_struct *tty, int poll) { … } /** * 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(const struct tty_struct *tty, u8 **kbp, size_t *nr) { … } /** * 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(const struct tty_struct *tty, u8 **kbp, size_t *nr) { … } /* * 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 n_tty_data *ldata) { … } /** * 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) { … } /** * 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, u8 *kbuf, size_t nr, void **cookie, unsigned long offset) { … } /** * 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 u8 *buf, size_t nr) { … } /** * 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) { … } static unsigned long inq_canon(struct n_tty_data *ldata) { … } static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) { … } static struct tty_ldisc_ops n_tty_ops = …; /** * 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) { … } EXPORT_SYMBOL_GPL(…); void __init n_tty_init(void) { … }
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