n_tty: Replace echo_cnt with computed value

Prepare for lockless echo_buf handling; compute current byte count
of echo_buf from head and tail indices.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 18d72a0258cebc8c9dff9f0e334f4b748d09dc65..8406a23ee92096f8b047dca5bae5942df3a22cde 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -110,7 +110,6 @@ struct n_tty_data {
        unsigned char *echo_buf;
        size_t echo_head;
        size_t echo_tail;
-       unsigned int echo_cnt;
 
        /* protected by output lock */
        unsigned int column;
@@ -336,7 +335,7 @@ 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_head = ldata->echo_tail = ldata->echo_cnt = 0;
+       ldata->echo_head = ldata->echo_tail  = 0;
        mutex_unlock(&ldata->echo_lock);
 
        ldata->erasing = 0;
@@ -654,7 +653,7 @@ static void process_echoes(struct tty_struct *tty)
        size_t tail;
        unsigned char c;
 
-       if (!ldata->echo_cnt)
+       if (ldata->echo_head == ldata->echo_tail)
                return;
 
        mutex_lock(&ldata->output_lock);
@@ -663,7 +662,7 @@ static void process_echoes(struct tty_struct *tty)
        space = tty_write_room(tty);
 
        tail = ldata->echo_tail;
-       nr = ldata->echo_cnt;
+       nr = ldata->echo_head - ldata->echo_tail;
        while (nr > 0) {
                c = echo_buf(ldata, tail);
                if (c == ECHO_OP_START) {
@@ -779,7 +778,6 @@ static void process_echoes(struct tty_struct *tty)
        }
 
        ldata->echo_tail = tail;
-       ldata->echo_cnt = nr;
 
        mutex_unlock(&ldata->echo_lock);
        mutex_unlock(&ldata->output_lock);
@@ -800,24 +798,20 @@ static void process_echoes(struct tty_struct *tty)
 
 static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
 {
-       if (ldata->echo_cnt == N_TTY_BUF_SIZE) {
+       if (ldata->echo_head - ldata->echo_tail == N_TTY_BUF_SIZE) {
                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 (echo_buf(ldata, head) == ECHO_OP_START) {
-                       if (echo_buf(ldata, head + 1) == ECHO_OP_ERASE_TAB) {
+                       if (echo_buf(ldata, head + 1) == ECHO_OP_ERASE_TAB)
                                ldata->echo_tail += 3;
-                               ldata->echo_cnt -= 2;
-                       } else {
+                       else
                                ldata->echo_tail += 2;
-                               ldata->echo_cnt -= 1;
-                       }
                } else
                        ldata->echo_tail++;
-       } else
-               ldata->echo_cnt++;
+       }
 
        *echo_buf_addr(ldata, ldata->echo_head++) = c;
 }