n_tty: Remove read_cnt

Storing the read_cnt creates an unnecessary shared variable
between the single-producer (n_tty_receive_buf()) and the
single-consumer (n_tty_read()).

Compute read_cnt from head & tail instead of storing.

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 b2fef10a0c628c27dc104ecd5834973d3f6af809..d159059560e8493c9d3f87ac064917836abefdbe 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -98,7 +98,6 @@ struct n_tty_data {
        char *read_buf;
        size_t read_head;
        size_t read_tail;
-       int read_cnt;
        int minimum_to_wake;
 
        unsigned char *echo_buf;
@@ -117,7 +116,7 @@ struct n_tty_data {
 
 static inline size_t read_cnt(struct n_tty_data *ldata)
 {
-       return ldata->read_cnt;
+       return ldata->read_head - ldata->read_tail;
 }
 
 static inline unsigned char read_buf(struct n_tty_data *ldata, size_t i)
@@ -198,7 +197,6 @@ static void put_tty_queue_nolock(unsigned char c, struct n_tty_data *ldata)
        if (read_cnt(ldata) < N_TTY_BUF_SIZE) {
                *read_buf_addr(ldata, ldata->read_head) = c;
                ldata->read_head++;
-               ldata->read_cnt++;
        }
 }
 
@@ -239,7 +237,7 @@ static void reset_buffer_flags(struct n_tty_data *ldata)
        unsigned long flags;
 
        raw_spin_lock_irqsave(&ldata->read_lock, flags);
-       ldata->read_head = ldata->read_tail = ldata->read_cnt = 0;
+       ldata->read_head = ldata->read_tail = 0;
        raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
 
        mutex_lock(&ldata->echo_lock);
@@ -942,16 +940,12 @@ static void eraser(unsigned char c, struct tty_struct *tty)
        else {
                if (!L_ECHO(tty)) {
                        raw_spin_lock_irqsave(&ldata->read_lock, flags);
-                       ldata->read_cnt -= ((ldata->read_head - ldata->canon_head) &
-                                         (N_TTY_BUF_SIZE - 1));
                        ldata->read_head = ldata->canon_head;
                        raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
                        return;
                }
                if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
                        raw_spin_lock_irqsave(&ldata->read_lock, flags);
-                       ldata->read_cnt -= ((ldata->read_head - ldata->canon_head) &
-                                         (N_TTY_BUF_SIZE - 1));
                        ldata->read_head = ldata->canon_head;
                        raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
                        finish_erasing(ldata);
@@ -989,7 +983,6 @@ static void eraser(unsigned char c, struct tty_struct *tty)
                cnt = ldata->read_head - head;
                raw_spin_lock_irqsave(&ldata->read_lock, flags);
                ldata->read_head = head;
-               ldata->read_cnt -= cnt;
                raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
                if (L_ECHO(tty)) {
                        if (L_ECHOPRT(tty)) {
@@ -1448,7 +1441,6 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
                i = min(count, i);
                memcpy(read_buf_addr(ldata, ldata->read_head), cp, i);
                ldata->read_head += i;
-               ldata->read_cnt += i;
                cp += i;
                count -= i;
 
@@ -1457,7 +1449,6 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
                i = min(count, i);
                memcpy(read_buf_addr(ldata, ldata->read_head), cp, i);
                ldata->read_head += i;
-               ldata->read_cnt += i;
                raw_spin_unlock_irqrestore(&ldata->read_lock, cpuflags);
        } else {
                for (i = count, p = cp, f = fp; i; i--, p++) {
@@ -1762,7 +1753,6 @@ static int copy_from_read_buf(struct tty_struct *tty,
                                ldata->icanon);
                raw_spin_lock_irqsave(&ldata->read_lock, flags);
                ldata->read_tail += n;
-               ldata->read_cnt -= n;
                /* Turn single EOF into zero-length read */
                if (L_EXTPROC(tty) && ldata->icanon && is_eof && !read_cnt(ldata))
                        n = 0;
@@ -1850,7 +1840,6 @@ static int canon_copy_from_read_buf(struct tty_struct *tty,
 
        raw_spin_lock_irqsave(&ldata->read_lock, flags);
        ldata->read_tail += c;
-       ldata->read_cnt -= c;
        if (found) {
                __clear_bit(eol, ldata->read_flags);
                /* this test should be redundant: