From 4db947d17c8c7dac3b344c8ce0a266f7be159200 Mon Sep 17 00:00:00 2001
From: David Gibson <david@gibson.dropbear.id.au>
Date: Fri, 8 Mar 2024 17:53:24 +1100
Subject: 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>
---
arp.c | 4 +---
tap.c | 38 +++++++++++++++++---------------------
tap.h | 2 +-
3 files changed, 19 insertions(+), 25 deletions(-)
diff --git a/arp.c b/arp.c
index a35c1b6..113cda2 100644
--- a/arp.c
+++ b/arp.c
@@ -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;
}
diff --git a/tap.c b/tap.c
index b6cc14c..13e4da7 100644
--- a/tap.c
+++ b/tap.c
@@ -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));
}
/**
diff --git a/tap.h b/tap.h
index c45aab3..aa3b1af 100644
--- a/tap.h
+++ b/tap.h
@@ -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,
--
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