tap: Split tap specific and L2 (ethernet) headers

In some places (well, actually only UDP now) we use struct tap_hdr to
represent both tap backend specific and L2 ethernet headers.  Handling
these together seemed like a good idea at the time, but Laurent's changes
in the TCP code working towards vhost-user support suggest that treating
them separately is more useful, more often.

Alter struct tap_hdr to represent only the TAP backend specific headers.
Updated related helpers and the UDP code to match.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 23 insertions, 21 deletions

diff --git a/tap.h b/tap.h
index 2adc4e2..dbc23b3 100644
--- a/tap.h
+++ b/tap.h
@@ -6,30 +6,28 @@
 #ifndef TAP_H
 #define TAP_H
 
+#define ETH_HDR_INIT(proto) { .h_proto = htons_constant(proto) }
+
 /**
- * struct tap_hdr - L2 and tap specific headers
+ * struct tap_hdr - tap backend specific headers
  * @vnet_len:	Frame length (for qemu socket transport)
- * @eh:		Ethernet header
  */
 struct tap_hdr {
 	uint32_t vnet_len;
-	struct ethhdr eh;
 } __attribute__((packed));
 
-#define TAP_HDR_INIT(proto) { .eh.h_proto = htons_constant(proto) }
-
 static inline size_t tap_hdr_len_(const struct ctx *c)
 {
 	if (c->mode == MODE_PASST)
 		return sizeof(struct tap_hdr);
 	else
-		return sizeof(struct ethhdr);
+		return 0;
 }
 
 /**
  * tap_frame_base() - Find start of tap frame
  * @c:		Execution context
- * @taph:	Pointer to L2 and tap specific header buffer
+ * @taph:	Pointer to tap specific header buffer
  *
  * Returns: pointer to the start of tap frame - suitable for an
  *          iov_base to be passed to tap_send_frames())
@@ -43,17 +41,16 @@ static inline void *tap_frame_base(const struct ctx *c, struct tap_hdr *taph)
  * tap_frame_len() - Finalize tap frame and return total length
  * @c:		Execution context
  * @taph:	Tap header to finalize
- * @plen:	L3 packet length (excludes L2 and tap specific headers)
+ * @plen:	L2 packet length (includes L2, excludes tap specific headers)
  *
- * Returns: length of the tap frame including L2 and tap specific
- *          headers - suitable for an iov_len to be passed to
- *          tap_send_frames()
+ * Returns: length of the tap frame including tap specific headers - suitable
+ *          for an iov_len to be passed to tap_send_frames()
  */
 static inline size_t tap_frame_len(const struct ctx *c, struct tap_hdr *taph,
 				   size_t plen)
 {
 	if (c->mode == MODE_PASST)
-		taph->vnet_len = htonl(plen + sizeof(taph->eh));
+		taph->vnet_len = htonl(plen);
 	return plen + tap_hdr_len_(c);
 }
 
diff --git a/udp.c b/udp.c
index 594ea19..4bf9059 100644
--- a/udp.c
+++ b/udp.c
@@ -173,7 +173,8 @@ static uint8_t udp_act[IP_VERSIONS][UDP_ACT_TYPE_MAX][DIV_ROUND_UP(NUM_PORTS, 8)
 /**
  * udp4_l2_buf_t - Pre-cooked IPv4 packet buffers for tap connections
  * @s_in:	Source socket address, filled in by recvmmsg()
- * @taph:	Tap-level headers (partially pre-filled)
+ * @taph:	Tap backend specific header
+ * @eh:		Prefilled ethernet header
  * @iph:	Pre-filled IP header (except for tot_len and saddr)
  * @uh:		Headroom for UDP header
  * @data:	Storage for UDP payload
@@ -182,6 +183,7 @@ static struct udp4_l2_buf_t {
 	struct sockaddr_in s_in;
 
 	struct tap_hdr taph;
+	struct ethhdr eh;
 	struct iphdr iph;
 	struct udphdr uh;
 	uint8_t data[USHRT_MAX -
@@ -192,7 +194,8 @@ udp4_l2_buf[UDP_MAX_FRAMES];
 /**
  * udp6_l2_buf_t - Pre-cooked IPv6 packet buffers for tap connections
  * @s_in6:	Source socket address, filled in by recvmmsg()
- * @taph:	Tap-level headers (partially pre-filled)
+ * @taph:	Tap backend specific header
+ * @eh:		Pre-filled ethernet header
  * @ip6h:	Pre-filled IP header (except for payload_len and addresses)
  * @uh:		Headroom for UDP header
  * @data:	Storage for UDP payload
@@ -202,10 +205,11 @@ struct udp6_l2_buf_t {
 #ifdef __AVX2__
 	/* Align ip6h to 32-byte boundary. */
 	uint8_t pad[64 - (sizeof(struct sockaddr_in6) + sizeof(struct ethhdr) +
-			  sizeof(uint32_t))];
+			  sizeof(struct tap_hdr))];
 #endif
 
 	struct tap_hdr taph;
+	struct ethhdr eh;
 	struct ipv6hdr ip6h;
 	struct udphdr uh;
 	uint8_t data[USHRT_MAX -
@@ -289,8 +293,8 @@ void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s)
 		struct udp4_l2_buf_t *b4 = &udp4_l2_buf[i];
 		struct udp6_l2_buf_t *b6 = &udp6_l2_buf[i];
 
-		eth_update_mac(&b4->taph.eh, eth_d, eth_s);
-		eth_update_mac(&b6->taph.eh, eth_d, eth_s);
+		eth_update_mac(&b4->eh, eth_d, eth_s);
+		eth_update_mac(&b6->eh, eth_d, eth_s);
 	}
 }
 
@@ -307,7 +311,7 @@ static void udp_sock4_iov_init_one(const struct ctx *c, size_t i)
 	struct iovec *tiov = &udp4_l2_iov_tap[i];
 
 	*buf = (struct udp4_l2_buf_t) {
-		.taph = TAP_HDR_INIT(ETH_P_IP),
+		.eh  = ETH_HDR_INIT(ETH_P_IP),
 		.iph = L2_BUF_IP4_INIT(IPPROTO_UDP)
 	};
 
@@ -335,7 +339,7 @@ static void udp_sock6_iov_init_one(const struct ctx *c, size_t i)
 	struct iovec *tiov = &udp6_l2_iov_tap[i];
 
 	*buf = (struct udp6_l2_buf_t) {
-		.taph = TAP_HDR_INIT(ETH_P_IPV6),
+		.eh   = ETH_HDR_INIT(ETH_P_IPV6),
 		.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP)
 	};
 
@@ -608,7 +612,7 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
 	b->uh.dest = htons(dstport);
 	b->uh.len = htons(datalen + sizeof(b->uh));
 
-	return tap_frame_len(c, &b->taph, ip_len);
+	return tap_frame_len(c, &b->taph, ip_len + sizeof(b->eh));
 }
 
 /**
@@ -676,7 +680,8 @@ static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *b,
 	b->uh.len = b->ip6h.payload_len;
 	csum_udp6(&b->uh, src, dst, b->data, datalen);
 
-	return tap_frame_len(c, &b->taph, payload_len + sizeof(b->ip6h));
+	return tap_frame_len(c, &b->taph, payload_len +
+			                  sizeof(b->ip6h) + sizeof(b->eh));
 }
 
 /**