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Commit 1bf931ab authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Greg Kroah-Hartman
Browse files

vcs: poll(): cope with a deallocated vt 



When VT_DISALLOCATE is used on a vt, user space waiting with poll() on
the corresponding /dev/vcs device is not awakened. This is now fixed by
returning POLLHUP|POLLERR to user space.

Also, in the normal screen update case, we don't set POLLERR anymore as
POLLPRI alone is a much more logical response in a non-error situation,
saving some confusion on the user space side. The only known user app
making use of poll() on /dev/vcs* is BRLTTY which is known to cope with
that change already, so the risk of breakage is pretty much nonexistent.

Signed-off-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8a085494

drivers/tty/vt/vc_screen.c

+15 −6
Original line number Diff line number Diff line
@@ -80,7 +80,7 @@ 
struct vcs_poll_data {

	struct notifier_block notifier;

	unsigned int cons_num;

	bool seen_last_update;

	int event;

	wait_queue_head_t waitq;

	struct fasync_struct *fasync;

};
@@ -94,7 +94,7 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param) 
		container_of(nb, struct vcs_poll_data, notifier);

	int currcons = poll->cons_num;



	if (code != VT_UPDATE)

	if (code != VT_UPDATE && code != VT_DEALLOCATE)

		return NOTIFY_DONE;



	if (currcons == 0)
@@ -104,7 +104,7 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param) 
	if (currcons != vc->vc_num)

		return NOTIFY_DONE;



	poll->seen_last_update = false;

	poll->event = code;

	wake_up_interruptible(&poll->waitq);

	kill_fasync(&poll->fasync, SIGIO, POLL_IN);

	return NOTIFY_OK;
@@ -261,7 +261,7 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) 


	poll = file->private_data;

	if (count && poll)

		poll->seen_last_update = true;

		poll->event = 0;

	read = 0;

	ret = 0;

	while (count) {
@@ -616,12 +616,21 @@ static __poll_t 
vcs_poll(struct file *file, poll_table *wait)

{

	struct vcs_poll_data *poll = vcs_poll_data_get(file);

	__poll_t ret = DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;

	__poll_t ret = DEFAULT_POLLMASK|EPOLLERR;



	if (poll) {

		poll_wait(file, &poll->waitq, wait);

		if (poll->seen_last_update)

		switch (poll->event) {

		case VT_UPDATE:

			ret = DEFAULT_POLLMASK|EPOLLPRI;

			break;

		case VT_DEALLOCATE:

			ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;

			break;

		case 0:

			ret = DEFAULT_POLLMASK;

			break;

		}

	}

	return ret;

}