arping: exit 0 if running in deadline mode and we see replies

The arping behavior when running in deadline mode without a packet
count (-w without -c) should match that of ping: any replies indicate
that the host is up and should result in a zero (success) exit status.

Fixes: iputils#392
Closes: iputils#395

Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Noah Meyerhans <noahm@debian.org>

arping.c

@@ -848,6 +848,8 @@ static int event_loop(struct run_state *ctl)
 	else if (ctl->dad && ctl->quit_on_reply)
 		/* Duplicate address detection mode return value */
 		rc |= !(ctl->brd_sent != ctl->received);
+	else if (ctl->timeout && !(ctl->count > 0))
+		rc |= !(ctl->received > 0);
 	else
 		rc |= (ctl->sent != ctl->received);
 	return rc;

doc/arping.xml

@@ -202,13 +202,13 @@ xml:id="man.arping">
         <listitem>
           <para>Specify a timeout, in seconds, before
           <command>arping</command> exits regardless of how many
-          packets have been sent or received. In this case
-          <command>arping</command> does not stop after
-          <emphasis remap='I'>count</emphasis> packet are sent, it
-          waits either for
-          <emphasis remap='I'>deadline</emphasis> expire or until
-          <emphasis remap='I'>count</emphasis> probes are
-          answered.</para>
+          packets have been sent or received.  If any replies are
+          received, exit with status 0, otherwise status 1.  When
+          combined with the <emphasis remap="I">count</emphasis>
+          option, exit with status 0 if <emphasis
+          remap="I">count</emphasis> replies are received before the
+          deadline expiration, otherwise status 1.
+	  </para>
         </listitem>
       </varlistentry>
       <varlistentry>