From 0cd8a05ec036ca8f950d4d4034a80bf485581b6a Mon Sep 17 00:00:00 2001
From: Jesse Gross <jesse@nicira.com>
Date: Tue, 17 Nov 2009 19:03:27 -0800
Subject: [PATCH 1/1] datapath: Allow minimum headroom to be set when copying
 buffers.

If we need to copy an sk_buff in order to make it writable, allow
the minimum headroom to be specified.  This ensures that if we
need to add additional data, such as a VLAN tag, we will not have
to make a second copy.

Solves bug #2197 in certain situations.
---
 datapath/actions.c | 25 +++++++++++++++++--------
 datapath/actions.h |  1 -
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/datapath/actions.c b/datapath/actions.c
index 226a4f91a..15263281b 100644
--- a/datapath/actions.c
+++ b/datapath/actions.c
@@ -22,12 +22,21 @@
 #include "actions.h"
 #include "openvswitch/datapath-protocol.h"
 
-struct sk_buff *
-make_writable(struct sk_buff *skb, gfp_t gfp)
+static struct sk_buff *
+make_writable(struct sk_buff *skb, unsigned min_headroom, gfp_t gfp)
 {
 	if (skb_shared(skb) || skb_cloned(skb)) {
-		struct sk_buff *nskb = skb_copy(skb, gfp);
+		struct sk_buff *nskb;
+		unsigned headroom = max(min_headroom, skb_headroom(skb));
+
+		nskb = skb_copy_expand(skb, headroom, skb_tailroom(skb), gfp);
 		if (nskb) {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,24)
+			/* Before 2.6.24 these fields were not copied when
+			 * doing an skb_copy_expand. */
+			nskb->ip_summed = skb->ip_summed;
+			nskb->csum = skb->csum;
+#endif
 #if defined(CONFIG_XEN) && LINUX_VERSION_CODE == KERNEL_VERSION(2,6,18)
 			/* These fields are copied in skb_clone but not in
 			 * skb_copy or related functions.  We need to manually
@@ -87,7 +96,7 @@ modify_vlan_tci(struct datapath *dp, struct sk_buff *skb,
 		mask = VLAN_PCP_MASK;
 	}
 
-	skb = make_writable(skb, gfp);
+	skb = make_writable(skb, VLAN_HLEN, gfp);
 	if (!skb)
 		return ERR_PTR(-ENOMEM);
 
@@ -175,7 +184,7 @@ modify_vlan_tci(struct datapath *dp, struct sk_buff *skb,
 static struct sk_buff *strip_vlan(struct sk_buff *skb,
 				  struct odp_flow_key *key, gfp_t gfp)
 {
-	skb = make_writable(skb, gfp);
+	skb = make_writable(skb, 0, gfp);
 	if (skb) {
 		vlan_pull_tag(skb);
 		key->dl_vlan = htons(ODP_VLAN_NONE);
@@ -187,7 +196,7 @@ static struct sk_buff *set_dl_addr(struct sk_buff *skb,
 				   const struct odp_action_dl_addr *a,
 				   gfp_t gfp)
 {
-	skb = make_writable(skb, gfp);
+	skb = make_writable(skb, 0, gfp);
 	if (skb) {
 		struct ethhdr *eh = eth_hdr(skb);
 		memcpy(a->type == ODPAT_SET_DL_SRC ? eh->h_source : eh->h_dest,
@@ -223,7 +232,7 @@ static struct sk_buff *set_nw_addr(struct sk_buff *skb,
 	if (key->dl_type != htons(ETH_P_IP))
 		return skb;
 
-	skb = make_writable(skb, gfp);
+	skb = make_writable(skb, 0, gfp);
 	if (skb) {
 		struct iphdr *nh = ip_hdr(skb);
 		u32 *f = a->type == ODPAT_SET_NW_SRC ? &nh->saddr : &nh->daddr;
@@ -260,7 +269,7 @@ set_tp_port(struct sk_buff *skb, struct odp_flow_key *key,
 	else
 		return skb;
 
-	skb = make_writable(skb, gfp);
+	skb = make_writable(skb, 0, gfp);
 	if (skb) {
 		struct udphdr *th = udp_hdr(skb);
 		u16 *f = a->type == ODPAT_SET_TP_SRC ? &th->source : &th->dest;
diff --git a/datapath/actions.h b/datapath/actions.h
index bda6d55a3..065c0e40e 100644
--- a/datapath/actions.h
+++ b/datapath/actions.h
@@ -16,7 +16,6 @@ struct sk_buff;
 struct odp_flow_key;
 union odp_action;
 
-struct sk_buff *make_writable(struct sk_buff *, gfp_t gfp);
 int dp_xmit_skb(struct sk_buff *);
 int execute_actions(struct datapath *dp, struct sk_buff *skb,
 		    struct odp_flow_key *key,
-- 
2.45.2