[PATCH Trusty SRU] n_tty: Fix poll() when TIME_CHAR and MIN_CHAR == 0

[tim.gardner at canonical.com]

From: Peter Hurley <peter at hurleysoftware.com>

BugLink: http://bugs.launchpad.net/bugs/1397976

Commit eafbe67f84761d787802e5113d895a316b6292fe,
  n_tty: Refactor input_available_p() by call site
broke poll() when TIME_CHAR(tty) and MIN_CHAR(tty) are both 0.

When TIME_CHAR and MIN_CHAR are both 0, input is available if the
read_cnt is 1 (not 0).

Reported-by: Eric Dumazet <edumazet at google.com>
Tested-by: Eric Dumazet <edumazet at google.com>
Reported-by: Stephane Eranian <eranian at google.com>
Tested-by: David Ahern <dsahern at gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme at redhat.com>
Signed-off-by: Peter Hurley <peter at hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit a5934804a834f525c9e6289935ceef65b952b101)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---

It appears we didn't get all of the relevant commits. This looks good for stable as well.
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1397976/comments/4

 drivers/tty/n_tty.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 3480a67..84dcdf4 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1961,7 +1961,7 @@ err:
 static inline int input_available_p(struct tty_struct *tty, int poll)
 {
 	struct n_tty_data *ldata = tty->disc_data;
-	int amt = poll && !TIME_CHAR(tty) ? MIN_CHAR(tty) : 1;
+	int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
 
 	if (ldata->icanon && !L_EXTPROC(tty)) {
 		if (ldata->canon_head != ldata->read_tail)
-- 
1.9.1