[B.A.T.M.A.N.] [PATCHv3] batman-adv: use __constant_htons when possible

[B.A.T.M.A.N.] [PATCHv3] batman-adv: use __constant_htons when possible

[Antonio Quartulli]

When comparing a network ordered value with a constant, it
is better to convert the constant at compile time by means
of __constant_htons() instead of converting the value at
runtime using ntohs().

This refactoring may slightly improve the code performance.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
---

v2:
- patch rebased on top of
"batman-adv: use VLAN_ETH_HLEN instead of sizeof(struct vlan_eth_hdr)"

v3:
- use __constant* for vlan_insert_tag() argument



 bridge_loop_avoidance.c | 14 +++++++-------
 gateway_client.c        |  4 ++--
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/bridge_loop_avoidance.c b/bridge_loop_avoidance.c
index 9e691b0..de02e7c 100644
--- a/bridge_loop_avoidance.c
+++ b/bridge_loop_avoidance.c
@@ -343,7 +343,7 @@ static void batadv_bla_send_claim(struct batadv_priv *bat_priv, uint8_t *mac,
 	}
 
 	if (vid & BATADV_VLAN_HAS_TAG)
-		skb = vlan_insert_tag(skb, htons(ETH_P_8021Q),
+		skb = vlan_insert_tag(skb, __constant_htons(ETH_P_8021Q),
 				      vid & VLAN_VID_MASK);
 
 	skb_reset_mac_header(skb);
@@ -863,25 +863,25 @@ static int batadv_bla_process_claim(struct batadv_priv *bat_priv,
 	struct arphdr *arphdr;
 	uint8_t *hw_src, *hw_dst;
 	struct batadv_bla_claim_dst *bla_dst;
-	uint16_t proto;
+	__be16 proto;
 	int headlen;
 	unsigned short vid = BATADV_NO_FLAGS;
 	int ret;
 
 	ethhdr = eth_hdr(skb);
 
-	if (ntohs(ethhdr->h_proto) == ETH_P_8021Q) {
+	if (ethhdr->h_proto == __constant_htons(ETH_P_8021Q)) {
 		vhdr = (struct vlan_ethhdr *)ethhdr;
 		vid = ntohs(vhdr->h_vlan_TCI) & VLAN_VID_MASK;
 		vid |= BATADV_VLAN_HAS_TAG;
-		proto = ntohs(vhdr->h_vlan_encapsulated_proto);
+		proto = vhdr->h_vlan_encapsulated_proto;
 		headlen = sizeof(*vhdr);
 	} else {
-		proto = ntohs(ethhdr->h_proto);
+		proto = ethhdr->h_proto;
 		headlen = ETH_HLEN;
 	}
 
-	if (proto != ETH_P_ARP)
+	if (proto != __constant_htons(ETH_P_ARP))
 		return 0; /* not a claim frame */
 
 	/* this must be a ARP frame. check if it is a claim. */
@@ -1375,7 +1375,7 @@ int batadv_bla_is_backbone_gw(struct sk_buff *skb,
 
 	ethhdr = (struct ethhdr *)(((uint8_t *)skb->data) + hdr_size);
 
-	if (ntohs(ethhdr->h_proto) == ETH_P_8021Q) {
+	if (ethhdr->h_proto == __constant_htons(ETH_P_8021Q)) {
 		if (!pskb_may_pull(skb, hdr_size + VLAN_ETH_HLEN))
 			return 0;
 
diff --git a/gateway_client.c b/gateway_client.c
index f59e58d..3cf92f8 100644
--- a/gateway_client.c
+++ b/gateway_client.c
@@ -682,11 +682,11 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
 
 	/* check for bootp port */
 	if ((proto == __constant_htons(ETH_P_IP)) &&
-	    (ntohs(udphdr->dest) != 67))
+	    (udphdr->dest != __constant_htons(67)))
 		return false;
 
 	if ((proto == __constant_htons(ETH_P_IPV6)) &&
-	    (ntohs(udphdr->dest) != 547))
+	    (udphdr->dest != __constant_htons(547)))
 		return false;
 
 	return true;
-- 
1.8.1.5

Re: [B.A.T.M.A.N.] [PATCHv3] batman-adv: use __constant_htons when possible

[Antonio Quartulli]

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On Fri, May 17, 2013 at 10:21:43AM +0200, Antonio Quartulli wrote:
> When comparing a network ordered value with a constant, it
> is better to convert the constant at compile time by means
> of __constant_htons() instead of converting the value at
> runtime using ntohs().
> 
> This refactoring may slightly improve the code performance.
> 
> Signed-off-by: Antonio Quartulli <ordex@autistici.org>

After discussing with Simon, we realised that using __constant_htons is useless
since htons is smart enough to be as efficient as his brother __constant*.

Therefore this patch will be re-arranged to use htons only.
It will still remove some ntohs and make use of htons at their place.


Cheers,

-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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