n_tty: Encapsulate minimum_to_wake within N_TTY

minimum_to_wake is unique to N_TTY processing, and belongs in
per-ldisc data.

Add the ldisc method, ldisc_ops::fasync(), to notify line disciplines
when signal-driven I/O is enabled or disabled. When enabled for N_TTY
(by fcntl(F_SETFL, O_ASYNC)), blocking reader/polls will be woken
for any readable input. When disabled, blocking reader/polls are not
woken until the read buffer is full.

Canonical mode (L_ICANON(tty), n_tty_data::icanon) is not affected by
the minimum_to_wake setting.

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

1 files changed, 9 insertions, 8 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 6464029e4860..bd88007fa6ea 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2138,6 +2138,7 @@ static unsigned int tty_poll(struct file *filp, poll_table *wait)
 static int __tty_fasync(int fd, struct file *filp, int on)
 {
         struct tty_struct *tty = file_tty(filp);
+        struct tty_ldisc *ldisc;
         unsigned long flags;
         int retval = 0;
 
@@ -2148,11 +2149,17 @@ static int __tty_fasync(int fd, struct file *filp, int on)
         if (retval <= 0)
                 goto out;
 
+        ldisc = tty_ldisc_ref(tty);
+        if (ldisc) {
+                if (ldisc->ops->fasync)
+                        ldisc->ops->fasync(tty, on);
+                tty_ldisc_deref(ldisc);
+        }
+
         if (on) {
                 enum pid_type type;
                 struct pid *pid;
-                if (!waitqueue_active(&tty->read_wait))
-                        tty->minimum_to_wake = 1;
+
                 spin_lock_irqsave(&tty->ctrl_lock, flags);
                 if (tty->pgrp) {
                         pid = tty->pgrp;
@@ -2165,13 +2172,7 @@ static int __tty_fasync(int fd, struct file *filp, int on)
                 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                 retval = __f_setown(filp, pid, type, 0);
                 put_pid(pid);
-                if (retval)
-                        goto out;
-        } else {
-                if (!tty->fasync && !waitqueue_active(&tty->read_wait))
-                        tty->minimum_to_wake = N_TTY_BUF_SIZE;
         }
-        retval = 0;
 out:
         return retval;
 }