Bugfix setting the timer interval from ttl.

And test reading updated file contents after the interval elapses.

src/tests/get.vtc

@@ -28,3 +28,33 @@ client c1 {
 	expect resp.status == 200
 	expect resp.http.Get == "foo bar baz quux"
 } -run
+
+varnish v1 -vcl+backend {
+	import ${vmod_file};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new rdr = file.reader("${tmpdir}/file", ttl=0.1s);
+	}
+
+	sub vcl_recv {
+		return (synth(200));
+	}
+
+	sub vcl_synth {
+		set resp.http.Get = rdr.get();
+		return (deliver);
+	}
+}
+
+client c1 -run
+
+shell {echo -n "quux baz bar foo" > ${tmpdir}/file}
+delay .1
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.Get == "quux baz bar foo"
+} -run

src/vmod_file.c

@@ -258,9 +258,9 @@ vmod_reader__init(VRT_CTX, struct VPFX(file_reader) **rdrp,
 	timerspec.it_value.tv_sec = 0;
 	timerspec.it_value.tv_nsec = 1;
 	timerspec.it_interval.tv_sec = (time_t)ttl;
-	assert(timerspec.it_interval.tv_sec - ttl < 1.);
+	assert(ttl - timerspec.it_interval.tv_sec < 1.);
 	timerspec.it_interval.tv_nsec
-		= (long)(1e9 * (timerspec.it_interval.tv_sec - ttl));
+		= (long)(1e9 * (ttl - timerspec.it_interval.tv_sec));
 
 	errno = 0;
 	if (timer_settime(timerid, 0, &timerspec, NULL) != 0) {