cdev: introduce client 'dead' state

Files have the disadvantage that the kernel (or in this case 'we') cannot
force a client to close it. Instead, we have to mark it as 'dead' and wait
until the client closes the file theirself.
While marked as 'dead' we always return EPIPE or signal EPOLLHUP so the
client will notice that the file is dead.

This fixes a bug where when we forced an unregistration of a cdev session,
the cdev_client went away too early and the user still had the file open.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>

src/kmscon_cdev.c

@@ -81,6 +81,7 @@ struct kmscon_cdev {
 struct cdev_client {
 	struct shl_dlist list;
 	struct kmscon_cdev *cdev;
+	bool dead;
 
 	struct tsm_screen *screen;
 	struct tsm_vte *vte;
@@ -164,7 +165,7 @@ err_unlock:
  * so you actually can run "agetty" on this fake-VT. When set into graphical
  * mode, the terminal is suspended and you can run an XServer on it. We emulate
  * the VT-switching signal-API, too. We release all DRM devices if a fake-VT is
- * active and reqcuire them afterwards. This allows the clients to actually
+ * active and reacquire them afterwards. This allows the clients to actually
  * implement graphical terminals. However, if you fail to release the DRM
  * devices, we actually try to kill the fake-VT so we can get access again.
  */
@@ -353,37 +354,6 @@ static void client_input_event(struct uterm_input *input,
 	}
 }
 
-static void client_free(struct cdev_client *client)
-{
-	struct cdev_reader *reader;
-	struct cdev_waiter *waiter;
-
-	log_debug("free fake TTY client %p", client);
-
-	shl_dlist_unlink(&client->list);
-	if (client->ph)
-		fuse_pollhandle_destroy(client->ph);
-
-	while (!shl_dlist_empty(&client->readers)) {
-		reader = shl_dlist_entry(client->readers.next,
-					 struct cdev_reader, list);
-		reader_free(reader, -EPIPE);
-	}
-
-	while (!shl_dlist_empty(&client->waiters)) {
-		waiter = shl_dlist_entry(client->waiters.next,
-					 struct cdev_waiter, list);
-		waiter_free(waiter, -EPIPE);
-	}
-
-	uterm_input_unregister_cb(client->cdev->input, client_input_event,
-				  client);
-	tsm_vte_unref(client->vte);
-	tsm_screen_unref(client->screen);
-	shl_ring_free(client->ring);
-	free(client);
-}
-
 static int client_activate(struct cdev_client *client)
 {
 	int ret;
@@ -428,6 +398,44 @@ static int client_deactivate(struct cdev_client *client)
 	return 0;
 }
 
+static void client_kill(struct cdev_client *client)
+{
+	struct cdev_reader *reader;
+	struct cdev_waiter *waiter;
+
+	if (client->dead) {
+		log_error("killing already dead client");
+		return;
+	}
+
+	log_debug("kill fake TTY client %p", client);
+
+	client->dead = true;
+
+	if (client->ph) {
+		fuse_notify_poll(client->ph);
+		fuse_pollhandle_destroy(client->ph);
+	}
+
+	while (!shl_dlist_empty(&client->readers)) {
+		reader = shl_dlist_entry(client->readers.next,
+					 struct cdev_reader, list);
+		reader_free(reader, -EPIPE);
+	}
+
+	while (!shl_dlist_empty(&client->waiters)) {
+		waiter = shl_dlist_entry(client->waiters.next,
+					 struct cdev_waiter, list);
+		waiter_free(waiter, -EPIPE);
+	}
+
+	uterm_input_unregister_cb(client->cdev->input, client_input_event,
+				  client);
+	tsm_vte_unref(client->vte);
+	tsm_screen_unref(client->screen);
+	shl_ring_free(client->ring);
+}
+
 static int client_session_event(struct kmscon_session *s,
 				struct kmscon_session_event *ev,
 				void *data)
@@ -440,7 +448,7 @@ static int client_session_event(struct kmscon_session *s,
 	case KMSCON_SESSION_DEACTIVATE:
 		return client_deactivate(client);
 	case KMSCON_SESSION_UNREGISTER:
-		client_free(client);
+		client_kill(client);
 		break;
 	}
 
@@ -528,7 +536,12 @@ err_free:
 
 static void client_destroy(struct cdev_client *client)
 {
-	kmscon_session_unregister(client->s);
+	log_debug("destroy client %p", client);
+
+	if (!client->dead)
+		kmscon_session_unregister(client->s);
+	shl_dlist_unlink(&client->list);
+	free(client);
 }
 
 /* This must be called after each event dispatch round. It cleans up all
@@ -613,6 +626,11 @@ static void ll_read(fuse_req_t req, size_t size, off_t off,
 		return;
 	}
 
+	if (client->dead) {
+		fuse_reply_err(req, EPIPE);
+		return;
+	}
+
 	if (off != 0) {
 		fuse_reply_err(req, EINVAL);
 		return;
@@ -661,6 +679,11 @@ static void ll_write(fuse_req_t req, const char *buf, size_t size, off_t off,
 		return;
 	}
 
+	if (client->dead) {
+		fuse_reply_err(req, EPIPE);
+		return;
+	}
+
 	ret = fuse_reply_write(req, size);
 	if (ret < 0)
 		return;
@@ -678,6 +701,14 @@ static void ll_poll(fuse_req_t req, struct fuse_file_info *fi,
 		return;
 	}
 
+	if (client->dead) {
+		if (ph)
+			fuse_pollhandle_destroy(ph);
+		fuse_reply_poll(req, EPOLLHUP | EPOLLIN | EPOLLOUT |
+				     EPOLLWRNORM | EPOLLRDNORM);
+		return;
+	}
+
 	if (client->ph)
 		fuse_pollhandle_destroy(client->ph);
 	client->ph = ph;
@@ -932,6 +963,11 @@ static void ll_ioctl(fuse_req_t req, int cmd, void *arg,
 		return;
 	}
 
+	if (client->dead) {
+		fuse_reply_err(req, EPIPE);
+		return;
+	}
+
 	/* TODO: fix compat-ioctls */
 	compat = !!(flags & FUSE_IOCTL_COMPAT);
 	if (compat) {