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54502cca7f
To send frames on the tap interface, the UDP uses a fairly complicated two
level batching. First multiple frames are gathered into a single "message"
for the qemu stream socket, then multiple messages are send with
sendmmsg(). We now have tap_send_frames() which already deals with sending
a number of frames, including batching and handling partial sends. Use
that to considerably simplify things.
This does make a couple of behavioural changes:
* We used to split messages to keep them under 32kiB (except when a
single frame was longer than that). The comments claim this is
needed to stop qemu from closing the connection, but we don't have any
equivalent logic for TCP. I wasn't able to reproduce the problem with
this series, although it was apparently easy to reproduce earlier.
My suspicion is that there was never an inherent need to keep messages
small, however with larger messages (and default kernel buffer sizes)
the chances of needing more than one resend for partial send()s is
greatly increased. We used not to correctly handle that case of
multiple resends, but now we do.
* Previously when we got a partial send on UDP, we would resend the
remainder of the entire "message", including multiple frames. The
common code now only resends the remainder of a single frame, simply
dropping any frames which weren't even partially sent. This is what
TCP always did and is probably a better idea for UDP too.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
159 lines
3.2 KiB
C
159 lines
3.2 KiB
C
// SPDX-License-Identifier: AGPL-3.0-or-later
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/* PASST - Plug A Simple Socket Transport
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* for qemu/UNIX domain socket mode
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*
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* PASTA - Pack A Subtle Tap Abstraction
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* for network namespace/tap device mode
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*
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* pcap.c - Packet capture for PASST/PASTA
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*
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* Copyright (c) 2021 Red Hat GmbH
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* Author: Stefano Brivio <sbrivio@redhat.com>
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*/
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#include <stdio.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <time.h>
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#include <errno.h>
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#include <net/ethernet.h>
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#include <netinet/in.h>
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#include <unistd.h>
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#include <net/if.h>
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#include "util.h"
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#include "passt.h"
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#include "log.h"
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#define PCAP_VERSION_MINOR 4
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static int pcap_fd = -1;
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/* See pcap.h from libpcap, or pcap-savefile(5) */
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static const struct {
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uint32_t magic;
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#define PCAP_MAGIC 0xa1b2c3d4
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uint16_t major;
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#define PCAP_VERSION_MAJOR 2
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uint16_t minor;
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#define PCAP_VERSION_MINOR 4
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int32_t thiszone;
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uint32_t sigfigs;
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uint32_t snaplen;
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uint32_t linktype;
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#define PCAP_LINKTYPE_ETHERNET 1
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} pcap_hdr = {
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PCAP_MAGIC, PCAP_VERSION_MAJOR, PCAP_VERSION_MINOR, 0, 0, ETH_MAX_MTU,
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PCAP_LINKTYPE_ETHERNET
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};
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struct pcap_pkthdr {
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uint32_t tv_sec;
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uint32_t tv_usec;
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uint32_t caplen;
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uint32_t len;
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};
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/**
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* pcap_frame() - Capture a single frame to pcap file with given timestamp
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* @pkt: Pointer to data buffer, including L2 headers
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* @len: L2 packet length
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* @tv: Timestamp
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*
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* Returns: 0 on success, -errno on error writing to the file
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*/
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static int pcap_frame(const char *pkt, size_t len, const struct timeval *tv)
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{
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struct pcap_pkthdr h;
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h.tv_sec = tv->tv_sec;
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h.tv_usec = tv->tv_usec;
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h.caplen = h.len = len;
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if (write(pcap_fd, &h, sizeof(h)) < 0 || write(pcap_fd, pkt, len) < 0)
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return -errno;
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return 0;
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}
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/**
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* pcap() - Capture a single frame to pcap file
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* @pkt: Pointer to data buffer, including L2 headers
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* @len: L2 packet length
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*/
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void pcap(const char *pkt, size_t len)
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{
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struct timeval tv;
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if (pcap_fd == -1)
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return;
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gettimeofday(&tv, NULL);
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if (pcap_frame(pkt, len, &tv) != 0)
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debug("Cannot log packet, length %lu", len);
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}
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/**
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* pcap_multiple() - Capture multiple frames
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* @iov: Array of iovecs, one entry per frame
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* @n: Number of frames to capture
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* @offset: Offset of the frame within each iovec buffer
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*/
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void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset)
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{
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struct timeval tv;
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unsigned int i;
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if (pcap_fd == -1)
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return;
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gettimeofday(&tv, NULL);
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for (i = 0; i < n; i++) {
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if (pcap_frame((char *)iov[i].iov_base + offset,
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iov[i].iov_len - offset, &tv) != 0) {
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debug("Cannot log packet, length %lu",
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iov->iov_len - offset);
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return;
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}
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}
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}
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/**
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* pcap_init() - Initialise pcap file
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* @c: Execution context
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*/
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void pcap_init(struct ctx *c)
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{
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int flags = O_WRONLY | O_CREAT | O_TRUNC;
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if (pcap_fd != -1)
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return;
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if (!*c->pcap)
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return;
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flags |= c->foreground ? O_CLOEXEC : 0;
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pcap_fd = open(c->pcap, flags, S_IRUSR | S_IWUSR);
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if (pcap_fd == -1) {
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perror("open");
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return;
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}
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info("Saving packet capture to %s", c->pcap);
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if (write(pcap_fd, &pcap_hdr, sizeof(pcap_hdr)) < 0)
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warn("Cannot write PCAP header: %s", strerror(errno));
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}
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