gossip: add COMPLETED bit to mark records which are complete.

This should detect partial writes more robustly, since we make a
separate pwrite() call to update this flag after the record is written.

Previously we were playing a bit loose with synchronization assumptions,
which seemed to work on Linux ext4, but not so well elsewhere.

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

devtools/create-gossipstore.c

@@ -47,7 +47,8 @@ static void write_outmsg(int outfd, const u8 *outmsg, u32 timestamp)
 {
 	struct gossip_hdr hdr;
 
-	hdr.len = cpu_to_be32(tal_count(outmsg));
+	hdr.flags = CPU_TO_BE16(GOSSIP_STORE_COMPLETED_BIT);
+	hdr.len = cpu_to_be16(tal_count(outmsg));
 	hdr.crc = cpu_to_be32(crc32c(timestamp, outmsg, tal_count(outmsg)));
 	hdr.timestamp = cpu_to_be32(timestamp);
 

devtools/dump-gossipstore.c

@@ -11,7 +11,7 @@
 
 /* Current versions we support */
 #define GSTORE_MAJOR 0
-#define GSTORE_MINOR 14
+#define GSTORE_MINOR 15
 
 int main(int argc, char *argv[])
 {