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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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2016-01-09 21:45:09 -08:00 committed by Greg Kroah-Hartman
parent 33d7136336
commit bee6741ca0
3 changed files with 0 additions and 19 deletions
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5
drivers/tty/n_tty.c
View File

@ -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,
};

8
drivers/tty/tty_io.c
View File

@ -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;

6
include/linux/tty_ldisc.h
View File

@ -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);