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From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>, passt-dev@passt.top
Cc: David Gibson <david@gibson.dropbear.id.au>
Subject: [PATCH v2 13/18] tap: Add "tap headers" abstraction
Date: Fri,  9 Dec 2022 16:42:23 +1100	[thread overview]
Message-ID: <20221209054228.4085990-14-david@gibson.dropbear.id.au> (raw)
In-Reply-To: <20221209054228.4085990-1-david@gibson.dropbear.id.au>

Currently both the TCP and UDP code need to deal in various places with the
details of the L2 headers, and also the tap-specific "vnet_len" header.
This makes abstracting the tap interface to new backends (e.g. vhost-user
or tun) more difficult.

To improve this abstraction, create a new 'tap_hdr' structure which
represents both L2 (always Ethernet at the moment, but might be vary in
future) and any additional tap specific headers (such as the qemu socket's
vnet_len field).  Provide helper functions and macros to initialize, update
and use it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tap.c | 15 +++++++++++++++
 tap.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/tap.c b/tap.c
index 558a734..d0dd72c 100644
--- a/tap.c
+++ b/tap.c
@@ -386,6 +386,21 @@ void tap_send_frames(struct ctx *c, const struct iovec *iov, size_t n)
 	pcap_multiple(iov, n, sizeof(uint32_t));
 }
 
+/**
+ * tap_update_mac() - Update tap L2 header with new Ethernet addresses
+ * @taph:	Tap headers to update
+ * @eth_d:	Ethernet destination address, NULL if unchanged
+ * @eth_s:	Ethernet source address, NULL if unchanged
+ */
+void tap_update_mac(struct tap_hdr *taph,
+		    const unsigned char *eth_d, const unsigned char *eth_s)
+{
+	if (eth_d)
+		memcpy(taph->eh.h_dest, eth_d, sizeof(taph->eh.h_dest));
+	if (eth_s)
+		memcpy(taph->eh.h_source, eth_s, sizeof(taph->eh.h_source));
+}
+
 PACKET_POOL_DECL(pool_l4, UIO_MAXIOV, pkt_buf);
 
 /**
diff --git a/tap.h b/tap.h
index ceac890..8fe460a 100644
--- a/tap.h
+++ b/tap.h
@@ -6,6 +6,55 @@
 #ifndef TAP_H
 #define TAP_H
 
+/**
+ * struct tap_hdr - L2 and tap 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)
+{
+	(void)c;
+	return sizeof(struct tap_hdr);
+}
+
+/**
+ * tap_iov_base() - Find start of tap frame
+ * @c:		Execution context
+ * @taph:	Pointer to L2 header buffer
+ *
+ * Returns: pointer to the start of tap frame - suitable for an
+ *          iov_base to be passed to tap_send_frames())
+ */
+static inline void *tap_iov_base(const struct ctx *c, struct tap_hdr *taph)
+{
+	return (char *)(taph + 1) - tap_hdr_len_(c);
+}
+
+/**
+ * tap_iov_len() - Finalize tap frame and return total length
+ * @c:		Execution context
+ * @taph:	Tap header to finalize
+ * @plen:	L2 payload length (excludes L2 and 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()
+ */
+static inline size_t tap_iov_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));
+	return plen + tap_hdr_len_(c);
+}
+
 struct in_addr tap_ip4_daddr(const struct ctx *c);
 void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
 		   struct in_addr dst, in_port_t dport,
@@ -23,6 +72,8 @@ void tap_icmp6_send(const struct ctx *c,
 		    void *in, size_t len);
 int tap_send(const struct ctx *c, const void *data, size_t len);
 void tap_send_frames(struct ctx *c, const struct iovec *iov, size_t n);
+void tap_update_mac(struct tap_hdr *taph,
+		    const unsigned char *eth_d, const unsigned char *eth_s);
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now);
 void tap_sock_init(struct ctx *c);
-- 
@@ -6,6 +6,55 @@
 #ifndef TAP_H
 #define TAP_H
 
+/**
+ * struct tap_hdr - L2 and tap 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)
+{
+	(void)c;
+	return sizeof(struct tap_hdr);
+}
+
+/**
+ * tap_iov_base() - Find start of tap frame
+ * @c:		Execution context
+ * @taph:	Pointer to L2 header buffer
+ *
+ * Returns: pointer to the start of tap frame - suitable for an
+ *          iov_base to be passed to tap_send_frames())
+ */
+static inline void *tap_iov_base(const struct ctx *c, struct tap_hdr *taph)
+{
+	return (char *)(taph + 1) - tap_hdr_len_(c);
+}
+
+/**
+ * tap_iov_len() - Finalize tap frame and return total length
+ * @c:		Execution context
+ * @taph:	Tap header to finalize
+ * @plen:	L2 payload length (excludes L2 and 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()
+ */
+static inline size_t tap_iov_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));
+	return plen + tap_hdr_len_(c);
+}
+
 struct in_addr tap_ip4_daddr(const struct ctx *c);
 void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
 		   struct in_addr dst, in_port_t dport,
@@ -23,6 +72,8 @@ void tap_icmp6_send(const struct ctx *c,
 		    void *in, size_t len);
 int tap_send(const struct ctx *c, const void *data, size_t len);
 void tap_send_frames(struct ctx *c, const struct iovec *iov, size_t n);
+void tap_update_mac(struct tap_hdr *taph,
+		    const unsigned char *eth_d, const unsigned char *eth_s);
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now);
 void tap_sock_init(struct ctx *c);
-- 
2.38.1


  parent reply	other threads:[~2022-12-09  5:42 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-09  5:42 [PATCH v2 00/18] RFC: Unify and simplify tap send path David Gibson
2022-12-09  5:42 ` [PATCH v2 01/18] pcap: Introduce pcap_frame() helper David Gibson
2023-01-04 17:45   ` Stefano Brivio
2023-01-05  4:47     ` David Gibson
2022-12-09  5:42 ` [PATCH v2 02/18] pcap: Replace pcapm() with pcap_multiple() David Gibson
2022-12-09  5:42 ` [PATCH v2 03/18] tcp: Combine two parts of passt tap send path together David Gibson
2022-12-09  5:42 ` [PATCH v2 04/18] tcp: Don't keep compute total bytes in a message until we need it David Gibson
2023-01-04 17:45   ` Stefano Brivio
2023-01-05  4:48     ` David Gibson
2022-12-09  5:42 ` [PATCH v2 05/18] tcp: Improve interface to tcp_l2_buf_flush() David Gibson
2023-01-04 17:45   ` Stefano Brivio
2023-01-05  4:53     ` David Gibson
2022-12-09  5:42 ` [PATCH v2 06/18] tcp: Combine two parts of pasta tap send path together David Gibson
2022-12-09  5:42 ` [PATCH v2 07/18] tap, tcp: Move tap send path to tap.c David Gibson
2022-12-09  5:42 ` [PATCH v2 08/18] util: Introduce hton*_constant() in place of #ifdefs David Gibson
2022-12-09  5:42 ` [PATCH v2 09/18] tcp, udp: Use named field initializers in iov_init functions David Gibson
2022-12-09  5:42 ` [PATCH v2 10/18] util: Parameterize ethernet header initializer macro David Gibson
2022-12-09  5:42 ` [PATCH v2 11/18] tcp: Remove redundant and incorrect initialization from *_iov_init() David Gibson
2022-12-09  5:42 ` [PATCH v2 12/18] tcp: Consolidate calculation of total frame size David Gibson
2022-12-09  5:42 ` David Gibson [this message]
2022-12-09  5:42 ` [PATCH v2 14/18] tcp: Use abstracted tap header David Gibson
2022-12-09  5:42 ` [PATCH v2 15/18] tap: Use different io vector bases depending on tap type David Gibson
2022-12-09  5:42 ` [PATCH v2 16/18] udp: Use abstracted tap header David Gibson
2022-12-09  5:42 ` [PATCH v2 17/18] udp: Use tap_send_frames() David Gibson
2023-01-04 17:45   ` Stefano Brivio
2023-01-05  4:54     ` David Gibson
2022-12-09  5:42 ` [PATCH v2 18/18] tap: Improve handling of partial frame sends David Gibson
2023-01-04 17:45   ` Stefano Brivio
2023-01-05  4:57     ` David Gibson
2023-01-04 17:45 ` [PATCH v2 00/18] RFC: Unify and simplify tap send path Stefano Brivio

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