[PATCH 6/9] wal: simplify watcher API

[Vladimir Davydov <vdavydov.dev@gmail.com>]

This patch reverts changes done in order to make WAL watcher API
suitable for notiying TX about WAL garbage collection triggered on
ENOSPC, namely:

 b073b0176704 wal: add event_mask to wal_watcher
 7077341ec5b3 wal: pass wal_watcher_msg to wal_watcher callback

We don't need them anymore, because now we piggyback the notification
on the WAL request message that triggered ENOSPC.
---
 src/box/relay.cc | 12 ++++--------
 src/box/wal.c    | 27 ++++++---------------------
 src/box/wal.h    | 25 ++++++-------------------
 3 files changed, 16 insertions(+), 48 deletions(-)

diff --git a/src/box/relay.cc b/src/box/relay.cc
index 0034f99a..0a1e95af 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -406,12 +406,9 @@ relay_schedule_pending_gc(struct relay *relay, const struct vclock *vclock)
 }
 
 static void
-relay_process_wal_event(struct wal_watcher_msg *msg)
+relay_process_wal_event(struct wal_watcher *watcher, unsigned events)
 {
-	assert((msg->events & (WAL_EVENT_WRITE | WAL_EVENT_ROTATE)) != 0);
-
-	struct relay *relay = container_of(msg->watcher, struct relay,
-					   wal_watcher);
+	struct relay *relay = container_of(watcher, struct relay, wal_watcher);
 	if (relay->state != RELAY_FOLLOW) {
 		/*
 		 * Do not try to send anything to the replica
@@ -421,7 +418,7 @@ relay_process_wal_event(struct wal_watcher_msg *msg)
 	}
 	try {
 		recover_remaining_wals(relay->r, &relay->stream, NULL,
-				       (msg->events & WAL_EVENT_ROTATE) != 0);
+				       (events & WAL_EVENT_ROTATE) != 0);
 	} catch (Exception *e) {
 		e->log();
 		diag_move(diag_get(), &relay->diag);
@@ -507,8 +504,7 @@ relay_subscribe_f(va_list ap)
 	};
 	trigger_add(&r->on_close_log, &on_close_log);
 	wal_set_watcher(&relay->wal_watcher, cord_name(cord()),
-			relay_process_wal_event, cbus_process,
-			WAL_EVENT_WRITE | WAL_EVENT_ROTATE);
+			relay_process_wal_event, cbus_process);
 
 	relay_set_cord_name(relay->io.fd);
 
diff --git a/src/box/wal.c b/src/box/wal.c
index c47535e4..31385642 100644
--- a/src/box/wal.c
+++ b/src/box/wal.c
@@ -1137,13 +1137,6 @@ wal_watcher_notify(struct wal_watcher *watcher, unsigned events)
 	assert(!rlist_empty(&watcher->next));
 
 	struct wal_watcher_msg *msg = &watcher->msg;
-
-	events &= watcher->event_mask;
-	if (events == 0) {
-		/* The watcher isn't interested in this event. */
-		return;
-	}
-
 	if (msg->cmsg.route != NULL) {
 		/*
 		 * If the notification message is still en route,
@@ -1163,7 +1156,10 @@ static void
 wal_watcher_notify_perform(struct cmsg *cmsg)
 {
 	struct wal_watcher_msg *msg = (struct wal_watcher_msg *) cmsg;
-	msg->watcher->cb(msg);
+	struct wal_watcher *watcher = msg->watcher;
+	unsigned events = msg->events;
+
+	watcher->cb(watcher, events);
 }
 
 static void
@@ -1216,9 +1212,8 @@ wal_watcher_detach(void *arg)
 
 void
 wal_set_watcher(struct wal_watcher *watcher, const char *name,
-		void (*watcher_cb)(struct wal_watcher_msg *),
-		void (*process_cb)(struct cbus_endpoint *),
-		unsigned event_mask)
+		void (*watcher_cb)(struct wal_watcher *, unsigned events),
+		void (*process_cb)(struct cbus_endpoint *))
 {
 	assert(journal_is_initialized(&wal_writer_singleton.base));
 
@@ -1228,7 +1223,6 @@ wal_set_watcher(struct wal_watcher *watcher, const char *name,
 	watcher->msg.events = 0;
 	watcher->msg.cmsg.route = NULL;
 	watcher->pending_events = 0;
-	watcher->event_mask = event_mask;
 
 	assert(lengthof(watcher->route) == 2);
 	watcher->route[0] = (struct cmsg_hop)
@@ -1249,15 +1243,6 @@ wal_clear_watcher(struct wal_watcher *watcher,
 		    wal_watcher_detach, watcher, process_cb);
 }
 
-/**
- * Notify all interested watchers about a WAL event.
- *
- * XXX: Note, this function iterates over all registered watchers,
- * including those that are not interested in the given event.
- * This is OK only as long as the number of events/watchers is
- * small. If this ever changes, we should consider maintaining
- * a separate watcher list per each event type.
- */
 static void
 wal_notify_watchers(struct wal_writer *writer, unsigned events)
 {
diff --git a/src/box/wal.h b/src/box/wal.h
index e5079552..1e070625 100644
--- a/src/box/wal.h
+++ b/src/box/wal.h
@@ -73,15 +73,9 @@ wal_init(enum wal_mode wal_mode, const char *wal_dirname, int64_t wal_max_rows,
 void
 wal_thread_stop();
 
-/**
- * A notification message sent from the WAL to a watcher
- * when a WAL event occurs.
- */
 struct wal_watcher_msg {
 	struct cmsg cmsg;
-	/** Pointer to the watcher this message is for. */
 	struct wal_watcher *watcher;
-	/** Bit mask of events, see wal_event. */
 	unsigned events;
 };
 
@@ -96,7 +90,7 @@ struct wal_watcher {
 	/** Link in wal_writer::watchers. */
 	struct rlist next;
 	/** The watcher callback function. */
-	void (*cb)(struct wal_watcher_msg *);
+	void (*cb)(struct wal_watcher *, unsigned events);
 	/** Pipe from the watcher to WAL. */
 	struct cpipe wal_pipe;
 	/** Pipe from WAL to the watcher. */
@@ -106,11 +100,6 @@ struct wal_watcher {
 	/** Message sent to notify the watcher. */
 	struct wal_watcher_msg msg;
 	/**
-	 * Bit mask of WAL events that this watcher is
-	 * interested in.
-	 */
-	unsigned event_mask;
-	/**
 	 * Bit mask of WAL events that happened while
 	 * the notification message was en route.
 	 * It indicates that the message must be resend
@@ -135,19 +124,17 @@ struct wal_watcher {
  * @param watcher     WAL watcher to register.
  * @param name        Name of the cbus endpoint at the caller's cord.
  * @param watcher_cb  Callback to invoke from the caller's cord
- *                    upon receiving a WAL event. It takes an object
- *                    of type wal_watcher_msg that stores a pointer
- *                    to the watcher and information about the event.
+ *                    upon receiving a WAL event. Apart from the
+ *                    watcher itself, it takes a bit mask of events.
+ *                    Events are described in wal_event enum.
  * @param process_cb  Function called to process cbus messages
  *                    while the watcher is being attached or NULL
  *                    if the cbus loop is running elsewhere.
- * @param event_mask  Bit mask of events the watcher is interested in.
  */
 void
 wal_set_watcher(struct wal_watcher *watcher, const char *name,
-		void (*watcher_cb)(struct wal_watcher_msg *),
-		void (*process_cb)(struct cbus_endpoint *),
-		unsigned event_mask);
+		void (*watcher_cb)(struct wal_watcher *, unsigned events),
+		void (*process_cb)(struct cbus_endpoint *));
 
 /**
  * Unsubscribe from WAL events.
-- 
2.11.0