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tap: Add "tap headers" abstraction

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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>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-01-06 11:43:17 +11:00 committed by Stefano Brivio
parent e4443ba9bd
commit 4b3d38a069
2 changed files with 66 additions and 0 deletions
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15
tap.c
View File

@ -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);
/**

51
tap.h
View File

@ -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);