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: 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 c1c721f..18d72a0 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -108,7 +108,8 @@
/* 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 @@
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 @@
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 @@
{
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 @@
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 @@
* 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 @@
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 @@
tty_put_char(tty, ECHO_OP_START);
ldata->column++;
space--;
- cp += 2;
+ tail += 2;
nr -= 2;
break;
@@ -751,7 +755,7 @@
tty_put_char(tty, op ^ 0100);
ldata->column += 2;
space -= 2;
- cp += 2;
+ tail += 2;
nr -= 2;
}
@@ -769,24 +773,13 @@
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_cnt = nr;
- }
+ ldata->echo_tail = tail;
+ ldata->echo_cnt = nr;
mutex_unlock(&ldata->echo_lock);
mutex_unlock(&ldata->output_lock);
@@ -807,37 +800,26 @@
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;
}
/**