gossipd: have gossip_store_load() return a timestamp.

This is the modified-time of the file.  We have to store it internally
since we overwrite the gossip file with compaction on startup.

This means the "are we behind on gossip?" heuristic is no longer inside
gossip_store.c, which is cleaner.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/gossip_store.c

@@ -15,6 +15,7 @@
 #include <gossipd/gen_gossip_store.h>
 #include <gossipd/gen_gossip_wire.h>
 #include <stdio.h>
+#include <sys/stat.h>
 #include <sys/uio.h>
 #include <unistd.h>
 #include <wire/gen_peer_wire.h>
@@ -48,6 +49,9 @@ struct gossip_store {
 	/* Disable compaction if we encounter an error during a prior
 	 * compaction */
 	bool disable_compaction;
+
+	/* Timestamp of store when we opened it (0 if we created it) */
+	u32 timestamp;
 };
 
 static void gossip_store_destroy(struct gossip_store *gs)
@@ -111,16 +115,24 @@ static bool append_msg(int fd, const u8 *msg, u32 timestamp, u64 *len)
 
 /* Read gossip store entries, copy non-deleted ones.  This code is written
  * as simply and robustly as possible! */
-static void gossip_store_compact_offline(void)
+static u32 gossip_store_compact_offline(void)
 {
 	size_t count = 0, deleted = 0;
 	int old_fd, new_fd;
 	struct gossip_hdr hdr;
 	u8 version;
+	struct stat st;
 
 	old_fd = open(GOSSIP_STORE_FILENAME, O_RDONLY);
 	if (old_fd == -1)
-		return;
+		return 0;
+
+	if (fstat(old_fd, &st) != 0) {
+		status_broken("Could not stat gossip_store: %s",
+			      strerror(errno));
+		goto close_old;
+	}
+
 	new_fd = open(GOSSIP_STORE_TEMP_FILENAME, O_RDWR|O_TRUNC|O_CREAT, 0600);
 	if (new_fd < 0) {
 		status_broken(
@@ -182,13 +194,14 @@ static void gossip_store_compact_offline(void)
 	}
 	status_debug("gossip_store_compact_offline: %zu deleted, %zu copied",
 		     deleted, count);
-	return;
+	return st.st_mtime;
 
 close_and_delete:
 	close(new_fd);
 close_old:
 	close(old_fd);
 	unlink(GOSSIP_STORE_TEMP_FILENAME);
+	return 0;
 }
 
 struct gossip_store *gossip_store_new(struct routing_state *rstate,
@@ -197,7 +210,7 @@ struct gossip_store *gossip_store_new(struct routing_state *rstate,
 	struct gossip_store *gs = tal(rstate, struct gossip_store);
 	gs->count = gs->deleted = 0;
 	gs->writable = true;
-	gossip_store_compact_offline();
+	gs->timestamp = gossip_store_compact_offline();
 	gs->fd = open(GOSSIP_STORE_FILENAME, O_RDWR|O_CREAT, 0600);
 	if (gs->fd < 0)
 		status_failed(STATUS_FAIL_INTERNAL_ERROR,
@@ -624,7 +637,7 @@ int gossip_store_readonly_fd(struct gossip_store *gs)
 	return fd;
 }
 
-bool gossip_store_load(struct routing_state *rstate, struct gossip_store *gs)
+u32 gossip_store_load(struct routing_state *rstate, struct gossip_store *gs)
 {
 	struct gossip_hdr hdr;
 	u32 msglen, checksum;
@@ -634,8 +647,6 @@ bool gossip_store_load(struct routing_state *rstate, struct gossip_store *gs)
 	size_t stats[] = {0, 0, 0, 0};
 	struct timeabs start = time_now();
 	const u8 *chan_ann = NULL;
-	bool contents_ok;
-	u32 last_timestamp = 0;
 	u64 chan_ann_off = 0; /* Spurious gcc-9 (Ubuntu 9-20190402-1ubuntu1) 9.0.1 20190402 (experimental) warning */
 
 	gs->writable = false;
@@ -690,9 +701,6 @@ bool gossip_store_load(struct routing_state *rstate, struct gossip_store *gs)
 			/* Save for channel_amount (next msg) */
 			chan_ann = tal_steal(gs, msg);
 			chan_ann_off = gs->len;
-			/* If we have a channel_announcement, that's a reasonable
-			 * timestamp to use. */
-			last_timestamp = be32_to_cpu(hdr.timestamp);
 			break;
 		case WIRE_GOSSIP_STORE_PRIVATE_UPDATE:
 			if (!fromwire_gossip_store_private_update(tmpctx, msg, &msg)) {
@@ -742,8 +750,6 @@ bool gossip_store_load(struct routing_state *rstate, struct gossip_store *gs)
 	if (bad)
 		goto corrupt;
 
-	/* If last timestamp is within 24 hours, say we're OK. */
-	contents_ok = (last_timestamp >= gossip_time_now(rstate).ts.tv_sec - 24*3600);
 	goto out;
 
 badmsg:
@@ -763,7 +769,7 @@ corrupt:
 	remove_all_gossip(rstate);
 	gs->count = gs->deleted = 0;
 	gs->len = 1;
-	contents_ok = false;
+	gs->timestamp = 0;
 out:
 	gs->writable = true;
 	status_debug("total store load time: %"PRIu64" msec",
@@ -772,5 +778,5 @@ out:
 		     stats[0], stats[1], stats[2], stats[3], gs->deleted,
 		     gs->len);
 
-	return contents_ok;
+	return gs->timestamp;
 }

gossipd/gossip_store.h

@@ -24,9 +24,9 @@ struct gossip_store *gossip_store_new(struct routing_state *rstate,
  * @param rstate The routing state to load init.
  * @param gs  The `gossip_store` to read from
  *
- * Returns true if the store seems fully populated.
+ * Returns the last-modified time of the store, or 0 if it was created new.
  */
-bool gossip_store_load(struct routing_state *rstate, struct gossip_store *gs);
+u32 gossip_store_load(struct routing_state *rstate, struct gossip_store *gs);
 
 /**
  * Add a private channel_update message to the gossip_store

gossipd/gossipd.c

@@ -939,6 +939,7 @@ static struct io_plan *gossip_init(struct io_conn *conn,
 {
 	u32 *dev_gossip_time;
 	bool dev_fast_gossip, dev_fast_gossip_prune;
+	u32 timestamp;
 
 	if (!fromwire_gossipctl_init(daemon, msg,
 				     &chainparams,
@@ -964,7 +965,9 @@ static struct io_plan *gossip_init(struct io_conn *conn,
 					   dev_fast_gossip_prune);
 
 	/* Load stored gossip messages */
-	if (!gossip_store_load(daemon->rstate, daemon->rstate->gs))
+	timestamp = gossip_store_load(daemon->rstate, daemon->rstate->gs);
+	/* If gossip_store less than 24 hours old, say we're OK. */
+	if (timestamp < gossip_time_now(daemon->rstate).ts.tv_sec - 24*3600)
 		gossip_missing(daemon);
 
 	/* Now disable all local channels, they can't be connected yet. */