net: TX_RING and packet mmap

New packet socket feature that makes packet socket more efficient for
transmission.

- It reduces number of system call through a PACKET_TX_RING mechanism,
  based on PACKET_RX_RING (Circular buffer allocated in kernel space
  which is mmapped from user space).

- It minimizes CPU copy using fragmented SKB (almost zero copy).

Signed-off-by: Johann Baudy <johann.baudy@gnu-log.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if_packet.h

@@ -46,6 +46,8 @@ struct sockaddr_ll
 #define PACKET_VERSION			10
 #define PACKET_HDRLEN			11
 #define PACKET_RESERVE			12
+#define PACKET_TX_RING			13
+#define PACKET_LOSS			14
 
 struct tpacket_stats
 {
@@ -63,14 +65,22 @@ struct tpacket_auxdata
 	__u16		tp_vlan_tci;
 };
 
+/* Rx ring - header status */
+#define TP_STATUS_KERNEL	0x0
+#define TP_STATUS_USER		0x1
+#define TP_STATUS_COPY		0x2
+#define TP_STATUS_LOSING	0x4
+#define TP_STATUS_CSUMNOTREADY	0x8
+
+/* Tx ring - header status */
+#define TP_STATUS_AVAILABLE	0x0
+#define TP_STATUS_SEND_REQUEST	0x1
+#define TP_STATUS_SENDING	0x2
+#define TP_STATUS_WRONG_FORMAT	0x4
+
 struct tpacket_hdr
 {
 	unsigned long	tp_status;
-#define TP_STATUS_KERNEL	0
-#define TP_STATUS_USER		1
-#define TP_STATUS_COPY		2
-#define TP_STATUS_LOSING	4
-#define TP_STATUS_CSUMNOTREADY	8
 	unsigned int	tp_len;
 	unsigned int	tp_snaplen;
 	unsigned short	tp_mac;