[PATCH v3 2/5] wal: pass wal_watcher_msg to wal_watcher callback

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

This should make it easier to pass some extra information along with the
event mask. For example, we will use it to pass the vclock of the oldest
stored WAL, which is needed for WAL auto-deletion.

Needed for #3397
---
 src/box/relay.cc |  7 ++++---
 src/box/wal.c    |  7 ++-----
 src/box/wal.h    | 16 +++++++++++-----
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/box/relay.cc b/src/box/relay.cc
index 0a1e95af..2a4cb412 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -406,9 +406,10 @@ relay_schedule_pending_gc(struct relay *relay, const struct vclock *vclock)
 }
 
 static void
-relay_process_wal_event(struct wal_watcher *watcher, unsigned events)
+relay_process_wal_event(struct wal_watcher_msg *msg)
 {
-	struct relay *relay = container_of(watcher, struct relay, wal_watcher);
+	struct relay *relay = container_of(msg->watcher, struct relay,
+					   wal_watcher);
 	if (relay->state != RELAY_FOLLOW) {
 		/*
 		 * Do not try to send anything to the replica
@@ -418,7 +419,7 @@ relay_process_wal_event(struct wal_watcher *watcher, unsigned events)
 	}
 	try {
 		recover_remaining_wals(relay->r, &relay->stream, NULL,
-				       (events & WAL_EVENT_ROTATE) != 0);
+				       (msg->events & WAL_EVENT_ROTATE) != 0);
 	} catch (Exception *e) {
 		e->log();
 		diag_move(diag_get(), &relay->diag);
diff --git a/src/box/wal.c b/src/box/wal.c
index b7acb50e..d231cc98 100644
--- a/src/box/wal.c
+++ b/src/box/wal.c
@@ -1046,10 +1046,7 @@ static void
 wal_watcher_notify_perform(struct cmsg *cmsg)
 {
 	struct wal_watcher_msg *msg = (struct wal_watcher_msg *) cmsg;
-	struct wal_watcher *watcher = msg->watcher;
-	unsigned events = msg->events;
-
-	watcher->cb(watcher, events);
+	msg->watcher->cb(msg);
 }
 
 static void
@@ -1102,7 +1099,7 @@ wal_watcher_detach(void *arg)
 
 void
 wal_set_watcher(struct wal_watcher *watcher, const char *name,
-		void (*watcher_cb)(struct wal_watcher *, unsigned events),
+		void (*watcher_cb)(struct wal_watcher_msg *),
 		void (*process_cb)(struct cbus_endpoint *))
 {
 	assert(journal_is_initialized(&wal_writer_singleton.base));
diff --git a/src/box/wal.h b/src/box/wal.h
index 8ef1fb1d..7371ce93 100644
--- a/src/box/wal.h
+++ b/src/box/wal.h
@@ -63,9 +63,15 @@ wal_init(enum wal_mode wal_mode, const char *wal_dirname,
 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;
 };
 
@@ -80,7 +86,7 @@ struct wal_watcher {
 	/** Link in wal_writer::watchers. */
 	struct rlist next;
 	/** The watcher callback function. */
-	void (*cb)(struct wal_watcher *, unsigned events);
+	void (*cb)(struct wal_watcher_msg *);
 	/** Pipe from the watcher to WAL. */
 	struct cpipe wal_pipe;
 	/** Pipe from WAL to the watcher. */
@@ -114,16 +120,16 @@ 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. Apart from the
- *                    watcher itself, it takes a bit mask of events.
- *                    Events are described in wal_event enum.
+ *                    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.
  * @param process_cb  Function called to process cbus messages
  *                    while the watcher is being attached or NULL
  *                    if the cbus loop is running elsewhere.
  */
 void
 wal_set_watcher(struct wal_watcher *watcher, const char *name,
-		void (*watcher_cb)(struct wal_watcher *, unsigned events),
+		void (*watcher_cb)(struct wal_watcher_msg *),
 		void (*process_cb)(struct cbus_endpoint *));
 
 /**
-- 
2.11.0