af_packet: TX_RING support for TPACKET_V3

Although TPACKET_V3 Rx has some benefits over TPACKET_V2 Rx, *_v3
does not currently have TX_RING support. As a result an application
that wants the best perf for Tx and Rx (e.g. to handle request/response
transacations) ends up needing 2 sockets, one with *_v2 for Tx and
another with *_v3 for Rx.

This patch enables TPACKET_V2 compatible Tx features in TPACKET_V3
so that an application can use a single descriptor to get the benefits
of _v3 RX_RING and _v2 TX_RING. An application may do a block-send by
first filling up multiple frames in the Tx ring and then triggering a
transmit. This patch only support fixed size Tx frames for TPACKET_V3,
and requires that tp_next_offset must be zero.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/packet_mmap.txt

@@ -565,7 +565,7 @@ TPACKET_V1 --> TPACKET_V2:
 		   (void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
 
 TPACKET_V2 --> TPACKET_V3:
-	- Flexible buffer implementation:
+	- Flexible buffer implementation for RX_RING:
 		1. Blocks can be configured with non-static frame-size
 		2. Read/poll is at a block-level (as opposed to packet-level)
 		3. Added poll timeout to avoid indefinite user-space wait
@@ -574,7 +574,12 @@ TPACKET_V2 --> TPACKET_V3:
 			4.1 block::timeout
 			4.2 tpkt_hdr::sk_rxhash
 	- RX Hash data available in user space
-	- Currently only RX_RING available
+	- TX_RING semantics are conceptually similar to TPACKET_V2;
+	  use tpacket3_hdr instead of tpacket2_hdr, and TPACKET3_HDRLEN
+	  instead of TPACKET2_HDRLEN. In the current implementation,
+	  the tp_next_offset field in the tpacket3_hdr MUST be set to
+	  zero, indicating that the ring does not hold variable sized frames.
+	  Packets with non-zero values of tp_next_offset will be dropped.
 
 -------------------------------------------------------------------------------
 + AF_PACKET fanout mode

net/packet/af_packet.c

@@ -409,6 +409,9 @@ static void __packet_set_status(struct packet_sock *po, void *frame, int status)
 		flush_dcache_page(pgv_to_page(&h.h2->tp_status));
 		break;
 	case TPACKET_V3:
+		h.h3->tp_status = status;
+		flush_dcache_page(pgv_to_page(&h.h3->tp_status));
+		break;
 	default:
 		WARN(1, "TPACKET version not supported.\n");
 		BUG();
@@ -432,6 +435,8 @@ static int __packet_get_status(struct packet_sock *po, void *frame)
 		flush_dcache_page(pgv_to_page(&h.h2->tp_status));
 		return h.h2->tp_status;
 	case TPACKET_V3:
+		flush_dcache_page(pgv_to_page(&h.h3->tp_status));
+		return h.h3->tp_status;
 	default:
 		WARN(1, "TPACKET version not supported.\n");
 		BUG();
@@ -2497,6 +2502,13 @@ static int tpacket_parse_header(struct packet_sock *po, void *frame,
 	ph.raw = frame;
 
 	switch (po->tp_version) {
+	case TPACKET_V3:
+		if (ph.h3->tp_next_offset != 0) {
+			pr_warn_once("variable sized slot not supported");
+			return -EINVAL;
+		}
+		tp_len = ph.h3->tp_len;
+		break;
 	case TPACKET_V2:
 		tp_len = ph.h2->tp_len;
 		break;
@@ -2516,6 +2528,9 @@ static int tpacket_parse_header(struct packet_sock *po, void *frame,
 		off_max = po->tx_ring.frame_size - tp_len;
 		if (po->sk.sk_type == SOCK_DGRAM) {
 			switch (po->tp_version) {
+			case TPACKET_V3:
+				off = ph.h3->tp_net;
+				break;
 			case TPACKET_V2:
 				off = ph.h2->tp_net;
 				break;
@@ -2525,6 +2540,9 @@ static int tpacket_parse_header(struct packet_sock *po, void *frame,
 			}
 		} else {
 			switch (po->tp_version) {
+			case TPACKET_V3:
+				off = ph.h3->tp_mac;
+				break;
 			case TPACKET_V2:
 				off = ph.h2->tp_mac;
 				break;
@@ -4113,11 +4131,6 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 	struct tpacket_req *req = &req_u->req;
 
 	lock_sock(sk);
-	/* Opening a Tx-ring is NOT supported in TPACKET_V3 */
-	if (!closing && tx_ring && (po->tp_version > TPACKET_V2)) {
-		net_warn_ratelimited("Tx-ring is not supported.\n");
-		goto out;
-	}
 
 	rb = tx_ring ? &po->tx_ring : &po->rx_ring;
 	rb_queue = tx_ring ? &sk->sk_write_queue : &sk->sk_receive_queue;
@@ -4177,11 +4190,19 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 			goto out;
 		switch (po->tp_version) {
 		case TPACKET_V3:
-		/* Transmit path is not supported. We checked
+			/* Block transmit is not supported yet */
-		 * it above but just being paranoid
+			if (!tx_ring) {
-		 */
-			if (!tx_ring)
 				init_prb_bdqc(po, rb, pg_vec, req_u);
+			} else {
+				struct tpacket_req3 *req3 = &req_u->req3;
+
+				if (req3->tp_retire_blk_tov ||
+				    req3->tp_sizeof_priv ||
+				    req3->tp_feature_req_word) {
+					err = -EINVAL;
+					goto out;
+				}
+			}
 			break;
 		default:
 			break;