Allow ttl=0s, so that no update checks are performed.

This falls out automatically from the use of POSIX timers, by
setting the interval to 0.

Whether or not the client nevertheless sees changes in the file
is platform-dependent, since mmap(2) leaves this unspecified for
MAP_PRIVATE. On Linux, changes are seen, and the mapping is
retained after the file is deleted (until munmap).

src/tests/get.vtc

@@ -83,6 +83,51 @@ logexpect l1 -v v1 -d 1 -g raw -q "Error" {
 	expect * 0 Error	{^vmod file failure: rdr: cannot read info about}
 } -run
 
+shell {echo -n "The quick brown fox jumps over the lazy dog." > ${tmpdir}/fox}
+
+varnish v1 -vcl {
+	import ${vmod_file};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new rdr = file.reader("${tmpdir}/fox", ttl=0s);
+	}
+
+	sub vcl_recv {
+		return (synth(200));
+	}
+
+	sub vcl_synth {
+		set resp.http.Get = rdr.get();
+		return (deliver);
+	}
+}
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.Get ~ "fox"
+} -run
+
+shell {echo -n "twentieth century fox" > ${tmpdir}/fox}
+delay .1
+
+# Whether or not the client sees the change, although no update checks
+# are performed, depends on whether changes in MAP_PRIVATE mapped
+# files are reflected in the mapped page. According to mmap(2), this
+# is unspecified. The change is apparently seen on Linux. Check the
+# test log to see if it happened on the present platform.
+client c1 -run
+
+shell {rm -f ${tmpdir}/fox}
+delay .1
+
+# On Linux at least, the mapping is retained after file deletion
+# (until munmap), so the client will still see the mapped contents.
+# XXX test on other platforms
+client c1 -run
+
 varnish v1 -errvcl {not a regular file} {
 	import ${vmod_file};
 	backend b { .host = "${bad_ip}"; }
@@ -101,7 +146,7 @@ varnish v1 -errvcl {vmod file failure: new rdr: name is empty} {
 	}
 }
 
-varnish v1 -errvcl {vmod file failure: new rdr: ttl -1.000 must be > 0s} {
+varnish v1 -errvcl {vmod file failure: new rdr: ttl -1.000 must be >= 0s} {
 	import ${vmod_file};
 	backend b { .host = "${bad_ip}"; }
 

src/vmod_file.c

@@ -207,8 +207,8 @@ vmod_reader__init(VRT_CTX, struct VPFX(file_reader) **rdrp,
 		VFAIL(ctx, "new %s: name is empty", vcl_name);
 		return;
 	}
-	if (ttl <= 0) {
-		VFAIL(ctx, "new %s: ttl %.03f must be > 0s", vcl_name, ttl);
+	if (ttl < 0) {
+		VFAIL(ctx, "new %s: ttl %.03f must be >= 0s", vcl_name, ttl);
 		return;
 	}