Phonet: zero-copy GPRS TX

Send aligned pipe payload if requested to do so. Then, the socket buffer
needs not be fragmented anymore.
Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/phonet/pep.h

@@ -44,6 +44,7 @@ struct pep_sock {
 	u8			rx_fc;	/* RX flow control */
 	u8			tx_fc;	/* TX flow control */
 	u8			init_enable;	/* auto-enable at creation */
+	u8			aligned;
 };
 
 static inline struct pep_sock *pep_sk(struct sock *sk)
@@ -139,6 +140,7 @@ enum {
 	PN_PIPE_SB_NEGOTIATED_FC,
 	PN_PIPE_SB_REQUIRED_FC_TX,
 	PN_PIPE_SB_PREFERRED_FC_RX,
+	PN_PIPE_SB_ALIGNED_DATA,
 };
 
 /* Phonet pipe flow control models */

net/phonet/pep.c

@@ -444,6 +444,7 @@ static int pep_connreq_rcv(struct sock *sk, struct sk_buff *skb)
 	struct sockaddr_pn dst;
 	u16 peer_type;
 	u8 pipe_handle, enabled, n_sb;
+	u8 aligned = 0;
 
 	if (!pskb_pull(skb, sizeof(*hdr) + 4))
 		return -EINVAL;
@@ -482,6 +483,9 @@ static int pep_connreq_rcv(struct sock *sk, struct sk_buff *skb)
 				return -EINVAL;
 			peer_type = (peer_type & 0xff00) | data[0];
 			break;
+		case PN_PIPE_SB_ALIGNED_DATA:
+			aligned = data[0] != 0;
+			break;
 		}
 		n_sb--;
 	}
@@ -513,6 +517,7 @@ static int pep_connreq_rcv(struct sock *sk, struct sk_buff *skb)
 	newpn->rx_credits = 0;
 	newpn->rx_fc = newpn->tx_fc = PN_LEGACY_FLOW_CONTROL;
 	newpn->init_enable = enabled;
+	newpn->aligned = aligned;
 
 	BUG_ON(!skb_queue_empty(&newsk->sk_receive_queue));
 	skb_queue_head(&newsk->sk_receive_queue, skb);
@@ -832,10 +837,14 @@ static int pipe_skb_send(struct sock *sk, struct sk_buff *skb)
 		return -ENOBUFS;
 	}
 
-	skb_push(skb, 3);
+	skb_push(skb, 3 + pn->aligned);
 	skb_reset_transport_header(skb);
 	ph = pnp_hdr(skb);
 	ph->utid = 0;
+	if (pn->aligned) {
+		ph->message_id = PNS_PIPE_ALIGNED_DATA;
+		ph->data[0] = 0; /* padding */
+	} else
 		ph->message_id = PNS_PIPE_DATA;
 	ph->pipe_handle = pn->pipe_handle;
 
@@ -930,6 +939,9 @@ int pep_write(struct sock *sk, struct sk_buff *skb)
 	struct sk_buff *rskb, *fs;
 	int flen = 0;
 
+	if (pep_sk(sk)->aligned)
+		return pipe_skb_send(sk, skb);
+
 	rskb = alloc_skb(MAX_PNPIPE_HEADER, GFP_ATOMIC);
 	if (!rskb) {
 		kfree_skb(skb);