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tty: clean up the tty time logic a bit

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We only care if anything other than the lower 3 bits of the tty has
changed, so just check that way, which makes it a bit faster, and more
obvious what is going on.  Also, document this for future developers to
understand why we did this.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
This commit is contained in:
Greg Kroah-Hartman 2015-03-26 23:10:27 +01:00
parent 23f5b3fdd0
commit fbf4763531
1 changed files with 8 additions and 2 deletions
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10
drivers/tty/tty_io.c
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@ -1025,11 +1025,17 @@ void start_tty(struct tty_struct *tty)
}
EXPORT_SYMBOL(start_tty);
/* We limit tty time update visibility to every 8 seconds or so. */
static void tty_update_time(struct timespec *time)
{
unsigned long sec = get_seconds();
if (abs(sec - time->tv_sec) & ~7)
/*
* We only care if the two values differ in anything other than the
* lower three bits (i.e every 8 seconds). If so, then we can update
* the time of the tty device, otherwise it could be construded as a
* security leak to let userspace know the exact timing of the tty.
*/
if ((sec ^ time->tv_sec) & ~7)
time->tv_sec = sec;
}