dccp: Clamping RTT values

This extracts the clamping part of dccp_sample_rtt() and makes it available
to other parts of the code (as e.g. used in the next patch).

Note: The function dccp_sample_rtt() now reduces to subtracting the elapsed
time. This could be eliminated but would require shorter prefixes and thus
is not done by this patch - maybe an idea for later.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

net/dccp/dccp.h

@@ -334,7 +334,14 @@ extern struct sk_buff *dccp_ctl_make_reset(struct sock *sk,
 extern int	   dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);
 extern void	   dccp_send_close(struct sock *sk, const int active);
 extern int	   dccp_invalid_packet(struct sk_buff *skb);
-extern u32	   dccp_sample_rtt(struct sock *sk, long delta);
+
+static inline u32  dccp_sane_rtt(long usec_sample)
+{
+	if (unlikely(usec_sample <= 0 || usec_sample > DCCP_SANE_RTT_MAX))
+		DCCP_WARN("RTT sample %ld out of bounds!\n", usec_sample);
+	return clamp_val(usec_sample, DCCP_SANE_RTT_MIN, DCCP_SANE_RTT_MAX);
+}
+extern u32 dccp_sample_rtt(struct sock *sk, long delta);
 
 static inline int dccp_bad_service_code(const struct sock *sk,
 					const __be32 service)

net/dccp/input.c

@@ -707,16 +707,7 @@ u32 dccp_sample_rtt(struct sock *sk, long delta)
 	/* dccpor_elapsed_time is either zeroed out or set and > 0 */
 	delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10;
 
-	if (unlikely(delta <= 0)) {
-		DCCP_WARN("unusable RTT sample %ld, using min\n", delta);
-		return DCCP_SANE_RTT_MIN;
-	}
-	if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
-		DCCP_WARN("RTT sample %ld too large, using max\n", delta);
-		return DCCP_SANE_RTT_MAX;
-	}
-
-	return delta;
+	return dccp_sane_rtt(delta);
 }
 
 EXPORT_SYMBOL_GPL(dccp_sample_rtt);