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>

1 files changed, 7 insertions, 13 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 18d72a0258ce..8406a23ee920 100644
--- 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;
 }