diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 640c9e8710449..8d80384df8744 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -118,6 +118,9 @@ struct n_tty_data { 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; @@ -333,6 +336,8 @@ static void reset_buffer_flags(struct n_tty_data *ldata) 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) @@ -1225,12 +1230,30 @@ static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c) return c == START_CHAR(tty) || c == STOP_CHAR(tty); } -/* Returns true if c is consumed as flow-control character */ -static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char 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, 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); @@ -1242,11 +1265,12 @@ static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c return true; } -static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c) +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)) + if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done)) return; if (L_ISIG(tty)) { @@ -1401,7 +1425,8 @@ static void n_tty_receive_char(struct tty_struct *tty, unsigned char c) put_tty_queue(c, ldata); } -static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c) +static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c, + bool lookahead_done) { if (I_ISTRIP(tty)) c &= 0x7f; @@ -1409,9 +1434,12 @@ static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c) c = tolower(c); if (I_IXON(tty)) { - if (c == STOP_CHAR(tty)) - stop_tty(tty); - else if (c == START_CHAR(tty) || + if (c == STOP_CHAR(tty)) { + if (!lookahead_done) + stop_tty(tty); + } else if (c == START_CHAR(tty) && lookahead_done) { + return; + } else if (c == START_CHAR(tty) || (tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) && c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) && c != SUSP_CHAR(tty))) { @@ -1457,6 +1485,27 @@ n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag) 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) @@ -1496,7 +1545,7 @@ n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp, static void n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp, - const char *fp, int count) + const char *fp, int count, bool lookahead_done) { char flag = TTY_NORMAL; @@ -1504,12 +1553,12 @@ n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp, if (fp) flag = *fp++; if (likely(flag == TTY_NORMAL)) - n_tty_receive_char_closing(tty, *cp++); + 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) + const unsigned char *cp, const char *fp, int count, bool lookahead_done) { struct n_tty_data *ldata = tty->disc_data; char flag = TTY_NORMAL; @@ -1540,7 +1589,7 @@ static void n_tty_receive_buf_standard(struct tty_struct *tty, } if (test_bit(c, ldata->char_map)) - n_tty_receive_char_special(tty, c); + n_tty_receive_char_special(tty, c, lookahead_done); else n_tty_receive_char(tty, c); } @@ -1551,21 +1600,30 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp, { 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)) - n_tty_receive_buf_closing(tty, cp, fp, count); - else { - n_tty_receive_buf_standard(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; @@ -2446,6 +2504,7 @@ static struct tty_ldisc_ops n_tty_ops = { .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, }; /** diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index bfa431a8e6902..754fa43670cc5 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -5,6 +5,7 @@ #include #include +#include #include #include #include @@ -104,6 +105,7 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size) p->size = size; p->next = NULL; p->commit = 0; + p->lookahead = 0; p->read = 0; p->flags = 0; } @@ -234,6 +236,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) buf->head = next; } buf->head->read = buf->head->commit; + buf->head->lookahead = buf->head->read; if (ld && ld->ops->flush_buffer) ld->ops->flush_buffer(tty); @@ -276,13 +279,15 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size, if (n != NULL) { n->flags = flags; buf->tail = n; - /* paired w/ acquire in flush_to_ldisc(); ensures - * flush_to_ldisc() sees buffer data. + /* + * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs() + * ensures they see all buffer data. */ smp_store_release(&b->commit, b->used); - /* paired w/ acquire in flush_to_ldisc(); ensures the - * latest commit value can be read before the head is - * advanced to the next buffer + /* + * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs() + * ensures the latest commit value can be read before the head + * is advanced to the next buffer. */ smp_store_release(&b->next, n); } else if (change) @@ -459,6 +464,40 @@ int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p, } EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf); +static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head) +{ + head->lookahead = max(head->lookahead, head->read); + + while (head) { + struct tty_buffer *next; + unsigned char *p, *f = NULL; + unsigned int count; + + /* + * Paired w/ release in __tty_buffer_request_room(); + * ensures commit value read is not stale if the head + * is advancing to the next buffer. + */ + next = smp_load_acquire(&head->next); + /* + * Paired w/ release in __tty_buffer_request_room() or in + * tty_buffer_flush(); ensures we see the committed buffer data. + */ + count = smp_load_acquire(&head->commit) - head->lookahead; + if (!count) { + head = next; + continue; + } + + p = char_buf_ptr(head, head->lookahead); + if (~head->flags & TTYB_NORMAL) + f = flag_buf_ptr(head, head->lookahead); + + port->client_ops->lookahead_buf(port, p, f, count); + head->lookahead += count; + } +} + static int receive_buf(struct tty_port *port, struct tty_buffer *head, int count) { @@ -496,7 +535,7 @@ static void flush_to_ldisc(struct work_struct *work) while (1) { struct tty_buffer *head = buf->head; struct tty_buffer *next; - int count; + int count, rcvd; /* Ldisc or user is trying to gain exclusive access */ if (atomic_read(&buf->priority)) @@ -519,10 +558,12 @@ static void flush_to_ldisc(struct work_struct *work) continue; } - count = receive_buf(port, head, count); - if (!count) + rcvd = receive_buf(port, head, count); + head->read += rcvd; + if (rcvd < count) + lookahead_bufs(port, head); + if (!rcvd) break; - head->read += count; if (need_resched()) cond_resched(); diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 880608a657734..dce08a6d7b5e8 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -43,6 +43,26 @@ static int tty_port_default_receive_buf(struct tty_port *port, return ret; } +static void tty_port_default_lookahead_buf(struct tty_port *port, const unsigned char *p, + const unsigned char *f, unsigned int count) +{ + struct tty_struct *tty; + struct tty_ldisc *disc; + + tty = READ_ONCE(port->itty); + if (!tty) + return; + + disc = tty_ldisc_ref(tty); + if (!disc) + return; + + if (disc->ops->lookahead_buf) + disc->ops->lookahead_buf(disc->tty, p, f, count); + + tty_ldisc_deref(disc); +} + static void tty_port_default_wakeup(struct tty_port *port) { struct tty_struct *tty = tty_port_tty_get(port); @@ -55,6 +75,7 @@ static void tty_port_default_wakeup(struct tty_port *port) const struct tty_port_client_operations tty_port_default_client_ops = { .receive_buf = tty_port_default_receive_buf, + .lookahead_buf = tty_port_default_lookahead_buf, .write_wakeup = tty_port_default_wakeup, }; EXPORT_SYMBOL_GPL(tty_port_default_client_ops); diff --git a/include/linux/tty_buffer.h b/include/linux/tty_buffer.h index 3b9d776042915..1796648c29073 100644 --- a/include/linux/tty_buffer.h +++ b/include/linux/tty_buffer.h @@ -15,6 +15,7 @@ struct tty_buffer { int used; int size; int commit; + int lookahead; /* Lazy update on recv, can become less than "read" */ int read; int flags; /* Data points here */ diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h index e85002b56752b..33678e1936f6a 100644 --- a/include/linux/tty_ldisc.h +++ b/include/linux/tty_ldisc.h @@ -186,6 +186,18 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass, * indicate all data received is %TTY_NORMAL. If assigned, prefer this * function for automatic flow control. * + * @lookahead_buf: [DRV] ``void ()(struct tty_struct *tty, + * const unsigned char *cp, const char *fp, int count) + * + * This function is called by the low-level tty driver for characters + * not eaten by ->receive_buf() or ->receive_buf2(). It is useful for + * processing high-priority characters such as software flow-control + * characters that could otherwise get stuck into the intermediate + * buffer until tty has room to receive them. Ldisc must be able to + * handle later a ->receive_buf() or ->receive_buf2() call for the + * same characters (e.g. by skipping the actions for high-priority + * characters already handled by ->lookahead_buf()). + * * @owner: module containting this ldisc (for reference counting) * * This structure defines the interface between the tty line discipline @@ -229,6 +241,8 @@ struct tty_ldisc_ops { void (*dcd_change)(struct tty_struct *tty, unsigned int status); int (*receive_buf2)(struct tty_struct *tty, const unsigned char *cp, const char *fp, int count); + void (*lookahead_buf)(struct tty_struct *tty, const unsigned char *cp, + const unsigned char *fp, unsigned int count); struct module *owner; }; diff --git a/include/linux/tty_port.h b/include/linux/tty_port.h index 58e9619116b75..fa3c3bdaa2347 100644 --- a/include/linux/tty_port.h +++ b/include/linux/tty_port.h @@ -40,6 +40,8 @@ struct tty_port_operations { struct tty_port_client_operations { int (*receive_buf)(struct tty_port *port, const unsigned char *, const unsigned char *, size_t); + void (*lookahead_buf)(struct tty_port *port, const unsigned char *cp, + const unsigned char *fp, unsigned int count); void (*write_wakeup)(struct tty_port *port); };