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(a)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);
--
2.38.1