seatd: Implement ping request to wake up later

When device open or close messages are sent to seatd, libseat must read
messages from the socket until it sees the associated response message.
This means that it may drain enable/disable seat events from the socket,
queueing them internally for deferred processing.

As the socket is drained, the caller will not wake from a poll and have
no reason to dispatch libseat. To ensure that these messages would not
be left in the queue, 6fa82930d0c5660eea3102989c765dc864514e36 made it
so that open/close calls would execute all queued events just before
returning.

Unfortunately, this had the side-effect of having events fire from the
stack of libseat_open_device or libseat_close_device, which we now see
cause problems in compositors. Specifically, an issue has been observed
where libinput end up calling libseat_close_device, which in turn
dispatch a disable seat event that calls libinput_suspend. libinput does
not like this.

Instead, remove the execution from libseat_open_device and
libseat_close_device, and instead make a "ping" request to seatd if
events have been queued. The response to this will wake us up and ensure
that dispatch is called.

1 files changed, 22 insertions, 0 deletions

diff --git a/seatd/client.c b/seatd/client.c
index 1bfe94a..220c5d3 100644
--- a/seatd/client.c
+++ b/seatd/client.c
@@ -309,6 +309,20 @@ error:
 	return client_send_error(client, errno);
 }
 
+static int handle_ping(struct client *client) {
+	struct proto_header header = {
+		.opcode = SERVER_PONG,
+		.size = 0,
+	};
+
+	if (connection_put(&client->connection, &header, sizeof header) == -1) {
+		log_errorf("Could not write response: %s", strerror(errno));
+		return -1;
+	}
+
+	return 0;
+}
+
 static int client_handle_opcode(struct client *client, uint16_t opcode, size_t size) {
 	int res = 0;
 	switch (opcode) {
@@ -372,6 +386,14 @@ static int client_handle_opcode(struct client *client, uint16_t opcode, size_t s
 		res = handle_disable_seat(client);
 		break;
 	}
+	case CLIENT_PING: {
+		if (size != 0) {
+			log_error("Protocol error: invalid ping message");
+			return -1;
+		}
+		res = handle_ping(client);
+		break;
+	}
 	default:
 		log_errorf("Protocol error: unknown opcode: %d", opcode);
 		res = -1;