diff --git a/respodns/dns.py b/respodns/dns.py
index bb0ace6..cf78378 100644
--- a/respodns/dns.py
+++ b/respodns/dns.py
@@ -215,9 +215,7 @@ async def main(db, filepaths, checks, opts: Options):
 
     pooler = make_pooler(opts.ip_simul, finisher)
 
-    blocking_file_io = False  # TODO: put in Options.
-
-    if blocking_file_io:
+    if opts.blocking_file_io:
         from .ip_util import read_ips
 
         seen = 0
diff --git a/respodns/structs.py b/respodns/structs.py
index f8d3691..c6d875f 100644
--- a/respodns/structs.py
+++ b/respodns/structs.py
@@ -16,7 +16,8 @@ class Options:
     impatient: bool = False  # reduce retries and times for timeouts
     early_stopping: bool = True  # stop at the first invalid domain
     dry: bool = True  # don't write anything to database
-    progress: bool = False
+    progress: bool = False  # periodically print progress to stderr
+    blocking_file_io: bool = False  # halt execution until inputs arrive
 
 
 @dataclass