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tap: Remove unhelpeful vnet_pre optimization from tap_send()

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Callers of tap_send() can optionally use a small optimization by adding
extra space for the 4 byte length header used on the qemu socket interface.
tap_ip_send() is currently the only user of this, but this is used only
for "slow path" ICMP and DHCP packets, so there's not a lot of value to
the optimization.

Worse, having the two paths here complicates the interface and makes future
cleanups difficult, so just remove it.  I have some plans to bring back the
optimization in a more general way in future, but for now it's just in the
way.

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 2022-10-19 11:43:51 +11:00 committed by Stefano Brivio
parent f72b63e92f
commit fb5d1c5d7d
5 changed files with 13 additions and 24 deletions
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2
arp.c
View File

@ -81,7 +81,7 @@ int arp(const struct ctx *c, const struct pool *p)
memcpy(eh->h_dest, eh->h_source, sizeof(eh->h_dest));
memcpy(eh->h_source, c->mac, sizeof(eh->h_source));
if (tap_send(c, eh, len, 0) < 0)
if (tap_send(c, eh, len) < 0)
perror("ARP: send");
return 1;

2
dhcp.c
View File

@ -377,7 +377,7 @@ int dhcp(const struct ctx *c, const struct pool *p)
memcpy(eh->h_dest, eh->h_source, ETH_ALEN);
memcpy(eh->h_source, c->mac, ETH_ALEN);
if (tap_send(c, eh, len, 0) < 0)
if (tap_send(c, eh, len) < 0)
perror("DHCP: send");
return 1;

2
ndp.c
View File

@ -200,7 +200,7 @@ dns_done:
memcpy(ehr->h_source, c->mac, ETH_ALEN);
ehr->h_proto = htons(ETH_P_IPV6);
if (tap_send(c, ehr, len, 0) < 0)
if (tap_send(c, ehr, len) < 0)
perror("NDP: send");
return 1;

29
tap.c
View File

@ -66,34 +66,24 @@ static PACKET_POOL_NOINIT(pool_tap6, TAP_MSGS, pkt_buf);
* @c: Execution context
* @data: Packet buffer
* @len: Total L2 packet length
* @vnet_pre: Buffer has four-byte headroom
*
* Return: return code from send() or write()
*/
int tap_send(const struct ctx *c, const void *data, size_t len, int vnet_pre)
int tap_send(const struct ctx *c, const void *data, size_t len)
{
if (vnet_pre)
pcap((char *)data + 4, len);
else
pcap(data, len);
pcap(data, len);
if (c->mode == MODE_PASST) {
int flags = MSG_NOSIGNAL | MSG_DONTWAIT;
uint32_t vnet_len = htonl(len);
if (vnet_pre) {
*((uint32_t *)data) = htonl(len);
len += 4;
} else {
uint32_t vnet_len = htonl(len);
if (send(c->fd_tap, &vnet_len, 4, flags) < 0)
return -1;
}
if (send(c->fd_tap, &vnet_len, 4, flags) < 0)
return -1;
return send(c->fd_tap, data, len, flags);
}
return write(c->fd_tap, (char *)data + (vnet_pre ? 4 : 0), len);
return write(c->fd_tap, (char *)data, len);
}
/**
@ -135,10 +125,9 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
const char *in, size_t len, uint32_t flow)
{
char buf[USHRT_MAX];
char *pkt = buf + 4;
struct ethhdr *eh;
eh = (struct ethhdr *)pkt;
eh = (struct ethhdr *)buf;
/* TODO: ARP table lookup */
memcpy(eh->h_dest, c->mac_guest, ETH_ALEN);
@ -174,7 +163,7 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
csum_icmp4(ih, ih + 1, len - sizeof(*ih));
}
if (tap_send(c, buf, len + sizeof(*iph) + sizeof(*eh), 1) < 0)
if (tap_send(c, buf, len + sizeof(*iph) + sizeof(*eh)) < 0)
debug("tap: failed to send %lu bytes (IPv4)", len);
} else {
struct ipv6hdr *ip6h = (struct ipv6hdr *)(eh + 1);
@ -215,7 +204,7 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
ip6h->flow_lbl[2] = (flow >> 0) & 0xff;
}
if (tap_send(c, buf, len + sizeof(*ip6h) + sizeof(*eh), 1) < 1)
if (tap_send(c, buf, len + sizeof(*ip6h) + sizeof(*eh)) < 1)
debug("tap: failed to send %lu bytes (IPv6)", len);
}
}

2
tap.h
View File

@ -11,7 +11,7 @@ const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
const struct in6_addr *src);
void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
const char *in, size_t len, uint32_t flow);
int tap_send(const struct ctx *c, const void *data, size_t len, int vnet_pre);
int tap_send(const struct ctx *c, const void *data, size_t len);
void tap_handler(struct ctx *c, int fd, uint32_t events,
const struct timespec *now);
void tap_sock_init(struct ctx *c);