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tap: Implement tap_send() "slow path" in terms of fast path 

Most times we send frames to the guest it goes via tap_send_frames().
However "slow path" protocols - ARP, ICMP, ICMPv6, DHCP and DHCPv6 - go
via tap_send().

As well as being a semantic duplication, tap_send() contains at least one
serious problem: it doesn't properly handle short sends, which can be fatal
on the qemu socket connection, since frame boundaries will get out of sync.

Rewrite tap_send() to call tap_send_frames().  While we're there, rename it
tap_send_single() for clarity.

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 2024-03-08 17:53:24 +11:00 committed by Stefano Brivio
parent 1ebe787fe4
commit 4db947d17c
3 changed files with 19 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arp.c
View File

@ -44,7 +44,6 @@ int arp(const struct ctx *c, const struct pool *p)
struct arphdr *ah;
struct arpmsg *am;
size_t len;
int ret;
eh = packet_get(p, 0, 0, sizeof(*eh), NULL);
ah = packet_get(p, 0, sizeof(*eh), sizeof(*ah), NULL);
@ -83,8 +82,7 @@ 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 ((ret = tap_send(c, eh, len)) < 0)
warn("ARP: send: %s", strerror(ret));
tap_send_single(c, eh, len);
return 1;
}

38
tap.c
View File

@ -67,28 +67,28 @@ static PACKET_POOL_NOINIT(pool_tap6, TAP_MSGS, pkt_buf);
#define FRAGMENT_MSG_RATE 10 /* # seconds between fragment warnings */
/**
* tap_send() - Send frame, with qemu socket header if needed
* tap_send_single() - Send a single frame
* @c: Execution context
* @data: Packet buffer
* @len: Total L2 packet length
*
* Return: return code from send() or write()
*/
int tap_send(const struct ctx *c, const void *data, size_t len)
void tap_send_single(const struct ctx *c, const void *data, size_t len)
{
pcap(data, len);
uint32_t vnet_len = htonl(len);
struct iovec iov[2];
size_t iovcnt = 0;
if (c->mode == MODE_PASST) {
int flags = MSG_NOSIGNAL | MSG_DONTWAIT;
uint32_t vnet_len = htonl(len);
if (send(c->fd_tap, &vnet_len, 4, flags) < 0)
return -1;
return send(c->fd_tap, data, len, flags);
iov[iovcnt].iov_base = &vnet_len;
iov[iovcnt].iov_len = sizeof(vnet_len);
iovcnt++;
}
return write(c->fd_tap, (char *)data, len);
iov[iovcnt].iov_base = (void *)data;
iov[iovcnt].iov_len = len;
iovcnt++;
tap_send_frames(c, iov, iovcnt, 1);
}
/**
@ -189,8 +189,7 @@ void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
csum_udp4(uh, src, dst, in, len);
memcpy(data, in, len);
if (tap_send(c, buf, len + (data - buf)) < 0)
debug("tap: failed to send %zu bytes (IPv4)", len);
tap_send_single(c, buf, len + (data - buf));
}
/**
@ -212,8 +211,7 @@ void tap_icmp4_send(const struct ctx *c, struct in_addr src, struct in_addr dst,
memcpy(icmp4h, in, len);
csum_icmp4(icmp4h, icmp4h + 1, len - sizeof(*icmp4h));
if (tap_send(c, buf, len + ((char *)icmp4h - buf)) < 0)
debug("tap: failed to send %zu bytes (IPv4)", len);
tap_send_single(c, buf, len + ((char *)icmp4h - buf));
}
/**
@ -274,8 +272,7 @@ void tap_udp6_send(const struct ctx *c,
csum_udp6(uh, src, dst, in, len);
memcpy(data, in, len);
if (tap_send(c, buf, len + (data - buf)) < 1)
debug("tap: failed to send %zu bytes (IPv6)", len);
tap_send_single(c, buf, len + (data - buf));
}
/**
@ -298,8 +295,7 @@ void tap_icmp6_send(const struct ctx *c,
memcpy(icmp6h, in, len);
csum_icmp6(icmp6h, src, dst, icmp6h + 1, len - sizeof(*icmp6h));
if (tap_send(c, buf, len + ((char *)icmp6h - buf)) < 1)
debug("tap: failed to send %zu bytes (IPv6)", len);
tap_send_single(c, buf, len + ((char *)icmp6h - buf));
}
/**

2
tap.h
View File

@ -72,7 +72,7 @@ void tap_udp6_send(const struct ctx *c,
void tap_icmp6_send(const struct ctx *c,
const struct in6_addr *src, const struct in6_addr *dst,
const void *in, size_t len);
int tap_send(const struct ctx *c, const void *data, size_t len);
void tap_send_single(const struct ctx *c, const void *data, size_t len);
size_t tap_send_frames(const struct ctx *c, const struct iovec *iov,
size_t bufs_per_frame, size_t nframes);
void eth_update_mac(struct ethhdr *eh,