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tty, n_tty: Remove fasync() ldisc notification

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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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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);