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Block when initially opening a TTY multiple times.

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In the original MPSAFE TTY code, I changed the behaviour by returning
EBUSY. I thought this made more sense, because it's basically a race to
see who gets the TTY first.

It turns out this is not a good change, because it also causes EBUSY to
be returned when another process is closing the TTY. This can happen
during startup, when /etc/rc (or one of its children) is still busy
draining its data and /sbin/init is attempting to open the TTY to spawn
a getty.

Reported by:	bz
Tested by:	bz
This commit is contained in:
Ed Schouten 2009-05-24 12:32:03 +00:00
parent 8aec91b5e8
commit 47e6a3971f
1 changed files with 11 additions and 5 deletions
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16
sys/kern/tty.c
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@ -206,6 +206,7 @@ ttydev_leave(struct tty *tp)
ttydevsw_close(tp);
tp->t_flags &= ~TF_OPENCLOSE;
cv_broadcast(&tp->t_dcdwait);
tty_rel_free(tp);
}
@ -231,13 +232,17 @@ ttydev_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
tty_unlock(tp);
return (ENXIO);
}
/*
* Prevent the TTY from being opened when being torn down or
* built up by unrelated processes.
* Block when other processes are currently opening or closing
* the TTY.
*/
if (tp->t_flags & TF_OPENCLOSE) {
tty_unlock(tp);
return (EBUSY);
while (tp->t_flags & TF_OPENCLOSE) {
error = tty_wait(tp, &tp->t_dcdwait);
if (error != 0) {
tty_unlock(tp);
return (error);
}
}
tp->t_flags |= TF_OPENCLOSE;
@ -299,6 +304,7 @@ ttydev_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
tp->t_flags |= TF_OPENED_IN;
done: tp->t_flags &= ~TF_OPENCLOSE;
cv_broadcast(&tp->t_dcdwait);
ttydev_leave(tp);
return (error);