log: block reporting on minor memleak.

Exception: Node /tmp/lightning-t5gxc6gs/test_closing_different_fees/lightning-2/ has memory leaks: [{'value': '0x55caa0a0b8d0', 'label': 'ccan/ccan/tal/str/str.c:90:char[]', 'backtrace': ['ccan/ccan/tal/tal.c:467 (tal_alloc_)', 'ccan/ccan/tal/tal.c:496 (tal_alloc_arr_)', 'ccan/ccan/tal/str/str.c:90 (tal_vfmt)', 'lightningd/log.c:131 (new_log)', 'lightningd/subd.c:632 (new_subd)', 'lightningd/subd.c:686 (new_peer_subd)', 'lightningd/peer_control.c:2487 (peer_accept_channel)', 'lightningd/peer_control.c:674 (peer_sent_nongossip)', 'lightningd/gossip_control.c:55 (peer_nongossip)', 'lightningd/gossip_control.c:142 (gossip_msg)', 'lightningd/subd.c:477 (sd_msg_read)', 'lightningd/subd.c:319 (read_fds)', 'ccan/ccan/io/io.c:59 (next_plan)', 'ccan/ccan/io/io.c:387 (do_plan)', 'ccan/ccan/io/io.c:397 (io_ready)', 'ccan/ccan/io/poll.c:305 (io_loop)', 'lightningd/lightningd.c:347 (main)', '(null):0 ((null))', '(null):0 ((null))', '(null):0 ((null))'], 'parents': ['lightningd/log.c:103:struct log_book', 'lightningd/lightningd.c:43:struct lightningd']}]

Technically, true, but we save more memory by sharing the prefix pointer
than we lose by leaking it.

However, we'd ideally refcount so it's freed if the log is freed and
all the entries using it are pruned from the log book.

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

lightningd/log.c

@@ -128,7 +128,8 @@ new_log(const tal_t *ctx, struct log_book *record, const char *fmt, ...)
 	log->lr = record;
 	va_start(ap, fmt);
 	/* log->lr owns this, since its entries keep a pointer to it. */
-	log->prefix = tal_vfmt(log->lr, fmt, ap);
+	/* FIXME: Refcount this! */
+	log->prefix = notleak(tal_vfmt(log->lr, fmt, ap));
 	va_end(ap);
 
 	return log;