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doc: Add mock of migration source and target

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These test programs show the migration of a TCP connection using the
passt-repair helper.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2025-02-02 10:38:46 +01:00
parent 52e57f9c9a
commit dcf014be88
5 changed files with 267 additions and 0 deletions

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doc/migration/.gitignore vendored Normal file
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/source
/target

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# SPDX-License-Identifier: GPL-2.0-or-later
#
# PASST - Plug A Simple Socket Transport
# for qemu/UNIX domain socket mode
#
# PASTA - Pack A Subtle Tap Abstraction
# for network namespace/tap device mode
#
# Copyright (c) 2025 Red Hat GmbH
# Author: Stefano Brivio <sbrivio@redhat.com>
TARGETS = source target
CFLAGS = -Wall -Wextra -pedantic
all: $(TARGETS)
$(TARGETS): %: %.c
clean:
rm -f $(TARGETS)

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<!---
SPDX-License-Identifier: GPL-2.0-or-later
Copyright (c) 2025 Red Hat GmbH
Author: Stefano Brivio <sbrivio@redhat.com>
-->
Migration
=========
These test programs show a migration of a TCP connection from one process to
another using the TCP_REPAIR socket option.
The two processes are a mock of the matching implementation in passt(1), and run
unprivileged, so they rely on the passt-repair helper to connect to them and set
or clear TCP_REPAIR on the connection socket, transferred to the helper using
SCM_RIGHTS.
The passt-repair helper needs to have the CAP_NET_ADMIN capability, or run as
root.
Example of usage
----------------
* Start the test server
$ nc -l 9999
* Start the source side of the TCP client (mock of the source instance of passt)
$ ./source 127.0.0.1 9999 9998 /tmp/repair.sock
* The client sends a test string, and waits for a connection from passt-repair
# passt-repair /tmp/repair.sock
* The socket is now in repair mode, and `source` dumps sequences, then exits
sending sequence: 3244673313
receiving sequence: 2250449386
* Continue the connection on the target side, restarting from those sequences
$ ./target 127.0.0.1 9999 9998 /tmp/repair.sock 3244673313 2250449386
* The target side now waits for a connection from passt-repair
# passt-repair /tmp/repair.sock
* The target side asks passt-repair to switch the socket to repair mode, sets up
the TCP sequences, then asks passt-repair to clear repair mode, and sends a
test string to the server

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// SPDX-License-Identifier: GPL-2.0-or-later
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* doc/migration/source.c - Mock of TCP migration source, use with passt-repair
*
* Copyright (c) 2025 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*/
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/tcp.h>
int main(int argc, char **argv)
{
struct sockaddr_in a = { AF_INET, htons(atoi(argv[3])), { 0 }, { 0 } };
struct addrinfo hints = { 0, AF_UNSPEC, SOCK_STREAM, 0, 0,
NULL, NULL, NULL };
struct sockaddr_un a_helper = { AF_UNIX, { 0 } };
int seq, s, s_helper;
int8_t cmd;
struct iovec iov = { &cmd, sizeof(cmd) };
char buf[CMSG_SPACE(sizeof(int))];
struct msghdr msg = { NULL, 0, &iov, 1, buf, sizeof(buf), 0 };
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
socklen_t seqlen = sizeof(int);
struct addrinfo *r;
(void)argc;
if (argc != 5) {
fprintf(stderr, "%s DST_ADDR DST_PORT SRC_PORT HELPER_PATH\n",
argv[0]);
return -1;
}
strcpy(a_helper.sun_path, argv[4]);
getaddrinfo(argv[1], argv[2], &hints, &r);
/* Connect socket to server and send some data */
s = socket(r->ai_family, SOCK_STREAM, IPPROTO_TCP);
setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &((int){ 1 }), sizeof(int));
bind(s, (struct sockaddr *)&a, sizeof(a));
connect(s, r->ai_addr, r->ai_addrlen);
send(s, "before migration\n", sizeof("before migration\n"), 0);
/* Wait for helper */
s_helper = socket(AF_UNIX, SOCK_STREAM, 0);
unlink(a_helper.sun_path);
bind(s_helper, (struct sockaddr *)&a_helper, sizeof(a_helper));
listen(s_helper, 1);
s_helper = accept(s_helper, NULL, NULL);
/* Set up message for helper, with socket */
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
memcpy(CMSG_DATA(cmsg), &s, sizeof(s));
/* Send command to helper: turn repair mode on, wait for reply */
cmd = TCP_REPAIR_ON;
sendmsg(s_helper, &msg, 0);
recv(s_helper, &((int8_t){ 0 }), 1, 0);
/* Terminate helper */
close(s_helper);
/* Get sending sequence */
seq = TCP_SEND_QUEUE;
setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &seq, sizeof(seq));
getsockopt(s, SOL_TCP, TCP_QUEUE_SEQ, &seq, &seqlen);
fprintf(stdout, "%u ", seq);
/* Get receiving sequence */
seq = TCP_RECV_QUEUE;
setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &seq, sizeof(seq));
getsockopt(s, SOL_TCP, TCP_QUEUE_SEQ, &seq, &seqlen);
fprintf(stdout, "%u\n", seq);
}

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// SPDX-License-Identifier: GPL-2.0-or-later
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* doc/migration/target.c - Mock of TCP migration target, use with passt-repair
*
* Copyright (c) 2025 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*/
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/tcp.h>
int main(int argc, char **argv)
{
struct sockaddr_in a = { AF_INET, htons(atoi(argv[3])), { 0 }, { 0 } };
struct addrinfo hints = { 0, AF_UNSPEC, SOCK_STREAM, 0, 0,
NULL, NULL, NULL };
struct sockaddr_un a_helper = { AF_UNIX, { 0 } };
int s, s_helper, seq;
int8_t cmd;
struct iovec iov = { &cmd, sizeof(cmd) };
char buf[CMSG_SPACE(sizeof(int))];
struct msghdr msg = { NULL, 0, &iov, 1, buf, sizeof(buf), 0 };
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
struct addrinfo *r;
(void)argc;
strcpy(a_helper.sun_path, argv[4]);
getaddrinfo(argv[1], argv[2], &hints, &r);
if (argc != 7) {
fprintf(stderr,
"%s DST_ADDR DST_PORT SRC_PORT HELPER_PATH SSEQ RSEQ\n",
argv[0]);
return -1;
}
/* Prepare socket, bind to source port */
s = socket(r->ai_family, SOCK_STREAM, IPPROTO_TCP);
setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &((int){ 1 }), sizeof(int));
bind(s, (struct sockaddr *)&a, sizeof(a));
/* Wait for helper */
s_helper = socket(AF_UNIX, SOCK_STREAM, 0);
unlink(a_helper.sun_path);
bind(s_helper, (struct sockaddr *)&a_helper, sizeof(a_helper));
listen(s_helper, 1);
s_helper = accept(s_helper, NULL, NULL);
/* Set up message for helper, with socket */
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
memcpy(CMSG_DATA(cmsg), &s, sizeof(s));
/* Send command to helper: turn repair mode on, wait for reply */
cmd = TCP_REPAIR_ON;
sendmsg(s_helper, &msg, 0);
recv(s_helper, &((int){ 0 }), 1, 0);
/* Set sending sequence */
seq = TCP_SEND_QUEUE;
setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &seq, sizeof(seq));
seq = atoi(argv[5]);
setsockopt(s, SOL_TCP, TCP_QUEUE_SEQ, &seq, sizeof(seq));
/* Set receiving sequence */
seq = TCP_RECV_QUEUE;
setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &seq, sizeof(seq));
seq = atoi(argv[6]);
setsockopt(s, SOL_TCP, TCP_QUEUE_SEQ, &seq, sizeof(seq));
/* Connect setting kernel state only, without actual SYN / handshake */
connect(s, r->ai_addr, r->ai_addrlen);
/* Send command to helper: turn repair mode off, wait for reply */
cmd = TCP_REPAIR_OFF;
sendmsg(s_helper, &msg, 0);
recv(s_helper, &((int8_t){ 0 }), 1, 0);
/* Terminate helper */
close(s_helper);
/* Send some more data */
send(s, "after migration\n", sizeof("after migration\n"), 0);
}