log: add ltmp convenience context.

It's sometimes nicer where you don't have a convenient tmpctx.

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

lightningd/log.c

@@ -108,6 +108,10 @@ struct log_book *new_log_book(const tal_t *ctx,
 	lr->init_time = time_now();
 	list_head_init(&lr->log);
 
+	/* In case ltmp not initialized, do so now. */
+	if (!ltmp)
+		ltmp = tal_tmpctx(lr);
+
 	return lr;
 }
 
@@ -185,6 +189,12 @@ static void add_entry(struct log *log, struct log_entry *l)
 		log_debug(log, "Log pruned %zu entries (mem %zu -> %zu)",
 			  deleted, old_mem, log->lr->mem_used);
 	}
+
+	/* Free up temporaries now if any */
+	if (tal_first(ltmp)) {
+		tal_free(ltmp);
+		ltmp = tal_tmpctx(log->lr);
+	}
 }
 
 static struct log_entry *new_log_entry(struct log *log, enum log_level level)

lightningd/log.h

@@ -129,6 +129,10 @@ void log_dump_to_file(int fd, const struct log_book *lr);
 void opt_register_logging(struct log *log);
 void crashlog_activate(struct log *log);
 
+/* Convenience parent for temporary allocations (eg. type_to_string)
+ * during log calls; freed after every log_*() */
+const tal_t *ltmp;
+
 /* Before the crashlog is activated, just prints to stderr. */
 void NORETURN PRINTF_FMT(1,2) fatal(const char *fmt, ...);
 #endif /* LIGHTNING_LIGHTNINGD_LOG_H */