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Commit bee6741c authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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tty, n_tty: Remove fasync() ldisc notification 



Only the N_TTY line discipline implements the signal-driven i/o
notification enabled/disabled by fcntl(F_SETFL, O_ASYNC). The ldisc
fasync() notification is sent to the ldisc when the enable state has
changed (the tty core is notified via the fasync() VFS file operation).

The N_TTY line discipline used the enable state to change the wakeup
condition (minimum_to_wake = 1) for notifying the signal handler i/o is
available. However, just the presence of data is sufficient and necessary
to signal i/o is available, so changing minimum_to_wake is unnecessary
(and creates a race condition with read() and poll() which may be
concurrently updating minimum_to_wake).

Furthermore, since the kill_fasync() VFS helper performs no action if
the fasync list is empty, calling unconditionally is preferred; if
signal driven i/o just has been disabled, no signal will be sent by
kill_fasync() anyway so notification of the change via the ldisc
fasync() method is superfluous.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 33d71363

drivers/tty/n_tty.c

+0 −5
Original line number Diff line number Diff line
@@ -2448,10 +2448,6 @@ static int n_tty_ioctl(struct tty_struct *tty, struct file *file, 
	}

}



static void n_tty_fasync(struct tty_struct *tty, int on)

{

}



static struct tty_ldisc_ops n_tty_ops = {

	.magic           = TTY_LDISC_MAGIC,

	.name            = "n_tty",
@@ -2465,7 +2461,6 @@ static struct tty_ldisc_ops n_tty_ops = { 
	.poll            = n_tty_poll,

	.receive_buf     = n_tty_receive_buf,

	.write_wakeup    = n_tty_write_wakeup,

	.fasync		 = n_tty_fasync,

	.receive_buf2	 = n_tty_receive_buf2,

};

drivers/tty/tty_io.c

+0 −8
Original line number Diff line number Diff line
@@ -2219,7 +2219,6 @@ 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;
@@ -2230,13 +2229,6 @@ 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;

include/linux/tty_ldisc.h

+0 −6
Original line number Diff line number Diff line
@@ -98,11 +98,6 @@ 
 *	seek to perform this action quickly but should wait until

 *	any pending driver I/O is completed.

 *

 * void (*fasync)(struct tty_struct *, int on)

 *

 *	Notify line discipline when signal-driven I/O is enabled or

 *	disabled.

 *

 * void (*dcd_change)(struct tty_struct *tty, unsigned int status)

 *

 *	Tells the discipline that the DCD pin has changed its status.
@@ -202,7 +197,6 @@ struct tty_ldisc_ops { 
			       char *fp, int count);

	void	(*write_wakeup)(struct tty_struct *);

	void	(*dcd_change)(struct tty_struct *, unsigned int);

	void	(*fasync)(struct tty_struct *tty, int on);

	int	(*receive_buf2)(struct tty_struct *, const unsigned char *cp,

				char *fp, int count);