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Commit addaebcc authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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n_tty: Use separate head and tail indices for echo_buf 



Instead of using a single index to track the current echo_buf position,
use a head index when adding to the buffer and a tail index when
consuming from the buffer. Allow these head and tail indices to wrap
at max representable value; perform modulo reduction via helper
functions when accessing the buffer.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ae56f330

drivers/tty/n_tty.c

+35 −53
Original line number Diff line number Diff line
@@ -108,7 +108,8 @@ struct n_tty_data { 


	/* protected by echo_lock */

	unsigned char *echo_buf;

	unsigned int echo_pos;

	size_t echo_head;

	size_t echo_tail;

	unsigned int echo_cnt;



	/* protected by output lock */
@@ -135,6 +136,16 @@ 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)

{

	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)];

}



static inline int tty_put_user(struct tty_struct *tty, unsigned char x,

			       unsigned char __user *ptr)

{
@@ -325,7 +336,7 @@ static void reset_buffer_flags(struct n_tty_data *ldata) 
	ldata->read_head = ldata->canon_head = ldata->read_tail = 0;



	mutex_lock(&ldata->echo_lock);

	ldata->echo_pos = ldata->echo_cnt = 0;

	ldata->echo_head = ldata->echo_tail = ldata->echo_cnt = 0;

	mutex_unlock(&ldata->echo_lock);



	ldata->erasing = 0;
@@ -640,8 +651,8 @@ static void process_echoes(struct tty_struct *tty) 
{

	struct n_tty_data *ldata = tty->disc_data;

	int	space, nr;

	size_t tail;

	unsigned char c;

	unsigned char *cp, *buf_end;



	if (!ldata->echo_cnt)

		return;
@@ -651,14 +662,12 @@ static void process_echoes(struct tty_struct *tty) 


	space = tty_write_room(tty);



	buf_end = ldata->echo_buf + N_TTY_BUF_SIZE;

	cp = ldata->echo_buf + ldata->echo_pos;

	tail = ldata->echo_tail;

	nr = ldata->echo_cnt;

	while (nr > 0) {

		c = *cp;

		c = echo_buf(ldata, tail);

		if (c == ECHO_OP_START) {

			unsigned char op;

			unsigned char *opp;

			int no_space_left = 0;



			/*
@@ -666,18 +675,13 @@ static void process_echoes(struct tty_struct *tty) 
			 * operation, get the next byte, which is either the

			 * op code or a control character value.

			 */

			opp = cp + 1;

			if (opp == buf_end)

				opp -= N_TTY_BUF_SIZE;

			op = *opp;

			op = echo_buf(ldata, tail + 1);



			switch (op) {

				unsigned int num_chars, num_bs;



			case ECHO_OP_ERASE_TAB:

				if (++opp == buf_end)

					opp -= N_TTY_BUF_SIZE;

				num_chars = *opp;

				num_chars = echo_buf(ldata, tail + 2);



				/*

				 * Determine how many columns to go back
@@ -703,20 +707,20 @@ static void process_echoes(struct tty_struct *tty) 
					if (ldata->column > 0)

						ldata->column--;

				}

				cp += 3;

				tail += 3;

				nr -= 3;

				break;



			case ECHO_OP_SET_CANON_COL:

				ldata->canon_column = ldata->column;

				cp += 2;

				tail += 2;

				nr -= 2;

				break;



			case ECHO_OP_MOVE_BACK_COL:

				if (ldata->column > 0)

					ldata->column--;

				cp += 2;

				tail += 2;

				nr -= 2;

				break;
@@ -729,7 +733,7 @@ static void process_echoes(struct tty_struct *tty) 
				tty_put_char(tty, ECHO_OP_START);

				ldata->column++;

				space--;

				cp += 2;

				tail += 2;

				nr -= 2;

				break;
@@ -751,7 +755,7 @@ static void process_echoes(struct tty_struct *tty) 
				tty_put_char(tty, op ^ 0100);

				ldata->column += 2;

				space -= 2;

				cp += 2;

				tail += 2;

				nr -= 2;

			}
@@ -769,24 +773,13 @@ static void process_echoes(struct tty_struct *tty) 
				tty_put_char(tty, c);

				space -= 1;

			}

			cp += 1;

			tail += 1;

			nr -= 1;

		}



		/* When end of circular buffer reached, wrap around */

		if (cp >= buf_end)

			cp -= N_TTY_BUF_SIZE;

	}



	if (nr == 0) {

		ldata->echo_pos = 0;

		ldata->echo_cnt = 0;

	} else {

		int num_processed = ldata->echo_cnt - nr;

		ldata->echo_pos += num_processed;

		ldata->echo_pos &= N_TTY_BUF_SIZE - 1;

	ldata->echo_tail = tail;

	ldata->echo_cnt = nr;

	}



	mutex_unlock(&ldata->echo_lock);

	mutex_unlock(&ldata->output_lock);
@@ -807,37 +800,26 @@ static void process_echoes(struct tty_struct *tty) 


static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)

{

	int	new_byte_pos;



	if (ldata->echo_cnt == N_TTY_BUF_SIZE) {

		/* Circular buffer is already at capacity */

		new_byte_pos = ldata->echo_pos;



		size_t head = ldata->echo_head;

		/*

		 * Since the buffer start position needs to be advanced,

		 * be sure to step by a whole operation byte group.

		 */

		if (ldata->echo_buf[ldata->echo_pos] == ECHO_OP_START) {

			if (ldata->echo_buf[(ldata->echo_pos + 1) &

					  (N_TTY_BUF_SIZE - 1)] ==

						ECHO_OP_ERASE_TAB) {

				ldata->echo_pos += 3;

		if (echo_buf(ldata, head) == ECHO_OP_START) {

			if (echo_buf(ldata, head + 1) == ECHO_OP_ERASE_TAB) {

				ldata->echo_tail += 3;

				ldata->echo_cnt -= 2;

			} else {

				ldata->echo_pos += 2;

				ldata->echo_tail += 2;

				ldata->echo_cnt -= 1;

			}

		} else {

			ldata->echo_pos++;

		}

		ldata->echo_pos &= N_TTY_BUF_SIZE - 1;

	} else {

		new_byte_pos = ldata->echo_pos + ldata->echo_cnt;

		new_byte_pos &= N_TTY_BUF_SIZE - 1;

		} else

			ldata->echo_tail++;

	} else

		ldata->echo_cnt++;

	}



	ldata->echo_buf[new_byte_pos] = c;

	*echo_buf_addr(ldata, ldata->echo_head++) = c;

}



/**