passt/qrap.c

// SPDX-License-Identifier: AGPL-3.0-or-later

/* PASST - Plug A Simple Socket Transport
 *
 * qrap.c - qemu wrapper connecting UNIX domain socket to file descriptor
 *
 * Copyright (c) 2020-2021 Red Hat GmbH
 * Author: Stefano Brivio <sbrivio@redhat.com>
 *
 * TODO: Implement this functionality directly in qemu: we have TCP and UDP
 * socket back-ends already.
 */

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <linux/limits.h>
#include <limits.h>
#include <fcntl.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <time.h>

#include "util.h"
#include "passt.h"
#include "arp.h"

static char *qemu_names[] = {
	"kvm",
	"qemu-kvm",
#ifdef ARCH
	( "qemu-system-" ARCH ),
#endif
	"/usr/libexec/qemu-kvm",
	NULL,
};

/**
 * struct drop_arg - Drop matching arguments on command line
 * @name:	Option name
 * @val:	Substring in option value, NULL matches any value
 */
static const struct drop_arg {
	char *name;
	char *val;
} drop_args[] = {
	{ "-netdev",	NULL },
	{ "-net",	NULL },
	{ "-device",	"virtio-net-pci," },
	{ "-device",	"virtio-net-ccw," },
	{ "-device",	"e1000," },
	{ "-device",	"e1000e," },
	{ "-device",	"rtl8139," },
	{ 0 },
};

/**
 * struct pci_dev - PCI devices to add on command line depending on machine name
 * @mach:		Machine name
 * @name:		Device ("-device") name to insert
 * @template:		Prefix for device specification (first part of address)
 * @template_post:	Suffix for device specification (last part of address)
 * @first:		First usable PCI address
 * @last:		Last usable PCI address
 */
static const struct pci_dev {
	char *mach;
	char *name;
	char *template;
	char *template_post;
	int first;
	int last;
} pci_devs[] = {
	{ "pc-q35",	"virtio-net-pci",
		"bus=pci.", ",addr=0x0",	3, /* 2: hotplug bus */	16 },
	{ "pc-",	"virtio-net-pci",
		"bus=pci.0,addr=0x", "",	2, /* 1: ISA bridge */	16 },
	{ "s390-ccw",	"virtio-net-ccw",
		"devno=fe.0.", "",		1,			16 },
	{ 0 },
};

#define DEFAULT_FD	5

/**
 * usage() - Print usage and exit
 * @name:	Executable name
 */
void usage(const char *name)
{
	fprintf(stderr, "Usage: %s [FDNUM QEMU_CMD] [QEMU_ARG]...\n", name);
	fprintf(stderr, "\n");
	fprintf(stderr, "If first and second arguments aren't a socket number\n"
			"and a path, %s will try to locate a qemu binary\n"
			"and directly patch the command line\n", name);

	exit(EXIT_FAILURE);
}

/**
 * main() - Entry point and main loop
 * @argc:	Argument count
 * @argv:	File descriptor number, then qemu with arguments
 *
 * Return: 0 once interrupted, non-zero on failure
 */
int main(int argc, char **argv)
{
	struct timeval tv = { .tv_sec = 0, .tv_usec = (long)(500 * 1000) };
	int i, s, qemu_argc = 0, addr_map = 0, has_dev = 0, retry_on_reset;
	char *qemu_argv[ARG_MAX], dev_str[ARG_MAX];
	struct sockaddr_un addr = {
		.sun_family = AF_UNIX,
	};
	const struct pci_dev *dev = NULL;
	long fd;
	struct {
		uint32_t vnet_len;
		struct ethhdr eh;
		struct arphdr ah;
		struct arpmsg am;
	} probe = {
		.vnet_len = htonl(42),
		{
			.h_dest   = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
			.h_source = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
			.h_proto  = htons(ETH_P_ARP),
		},
		{	.ar_hrd = htons(ARPHRD_ETHER),
			.ar_pro = htons(ETH_P_IP),
			.ar_hln = ETH_ALEN,
			.ar_pln = 4,
			.ar_op  = htons(ARPOP_REQUEST),
		},
		{
			.sha = { 0 }, .sip = { 0 }, .tha = { 0 }, .tip = { 0 },
		},
	};
	char probe_r;

	if (argc >= 3) {
		errno = 0;
		fd = strtol(argv[1], NULL, 0);
		if (fd >= 3 && fd < INT_MAX && !errno) {
			char env_path[ARG_MAX + 1], *p, command[ARG_MAX];

			strncpy(env_path, getenv("PATH"), ARG_MAX);
			p = strtok(env_path, ":");
			while (p) {
				snprintf(command, ARG_MAX, "%s/%s", p, argv[2]);
				if (!access(command, X_OK))
					goto valid_args;

				p = strtok(NULL, ":");
			}
		}
	}

	fd = DEFAULT_FD;

	for (i = 1; i < argc - 1; i++) {
		if (strcmp(argv[i], "-machine"))
			continue;

		for (dev = pci_devs; dev->mach; dev++) {
			if (strstr(argv[i + 1], dev->mach) == argv[i + 1])
				break;
		}
	}

	if (!dev || !dev->mach)
		dev = pci_devs;

	for (qemu_argc = 1, i = 1; i < argc; i++) {
		const struct drop_arg *a;

		for (a = drop_args; a->name; a++) {
			if (!strcmp(argv[i], a->name)) {
				if (!a->val)
					break;

				if (i + 1 < argc &&
				    strstr(argv[i + 1], a->val) == argv[i + 1])
					break;
			}
		}
		if (a->name) {
			i++;
			continue;
		}

		if (!strcmp(argv[i], "-device") && i + 1 < argc) {
			char *p;

			has_dev = 1;

			if ((p = strstr(argv[i + 1], dev->template))) {
				long n;

				n = strtol(p + strlen(dev->template), NULL, 16);
				if (!errno)
					addr_map |= (1 << n);
			}
		}

		qemu_argv[qemu_argc++] = argv[i];
	}

	for (i = dev->first; i < dev->last; i++) {
		if (!(addr_map & (1 << i)))
			break;
	}
	if (i == dev->last) {
		fprintf(stderr, "Couldn't find free address for device\n");
		usage(argv[0]);
	}

	if (has_dev) {
		qemu_argv[qemu_argc++] = "-device";
		snprintf(dev_str, ARG_MAX, "%s,%s%x%s,netdev=hostnet0,x-txburst=4096",
			 dev->name, dev->template, i, dev->template_post);
		qemu_argv[qemu_argc++] = dev_str;
	}

	qemu_argv[qemu_argc++] = "-netdev";
	qemu_argv[qemu_argc++] = "socket,fd=" STR(DEFAULT_FD) ",id=hostnet0";
	qemu_argv[qemu_argc] = NULL;

valid_args:
	for (i = 1; i < UNIX_SOCK_MAX; i++) {
		retry_on_reset = 50;

retry:
		s = socket(AF_UNIX, SOCK_STREAM, 0);
		if (s < 0) {
			perror("socket");
			exit(EXIT_FAILURE);
		}

		if (setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
			perror("setsockopt SO_RCVTIMEO");
		if (setsockopt(s, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)))
			perror("setsockopt SO_SNDTIMEO");

		snprintf(addr.sun_path, UNIX_PATH_MAX, UNIX_SOCK_PATH, i);
		if (connect(s, (const struct sockaddr *)&addr, sizeof(addr)))
			perror("connect");
		else if (send(s, &probe, sizeof(probe), 0) != sizeof(probe))
			perror("send");
		else if (recv(s, &probe_r, 1, MSG_PEEK) <= 0)
			perror("recv");
		else
			break;

		/* FIXME: in a KubeVirt environment, libvirtd invokes qrap three
		 * times in a strict sequence when a virtual machine needs to
		 * be started, namely, when:
		 * - the domain XML is saved
		 * - the domain is started (for "probing")
		 * - the virtual machine is started for real
		 * and it often happens that the qemu process is still running
		 * when qrap is invoked again, so passt will refuse the new
		 * connection because the previous one is still active. This
		 * overlap seems to be anywhere between 0 and 3ms.
		 *
		 * If we get a connection reset, retry a few times, to allow for
		 * the previous qemu instance to terminate and, in turn, for the
		 * connection to passt to be closed.
		 *
		 * This should be fixed in libvirt instead. It probably makes
		 * sense to check this behaviour once native libvirt support is
		 * there, and this implies native qemu support too, so at that
		 * point qrap will have no reason to exist anymore -- that is,
		 * this FIXME will probably remain until the tool itself is
		 * obsoleted.
		 */
		if (retry_on_reset && errno == ECONNRESET) {
			retry_on_reset--;
			usleep(50 * 1000);
			goto retry;
		}

		fprintf(stderr, "Probe of %s failed\n", addr.sun_path);

		close(s);
	}

	if (i == UNIX_SOCK_MAX) {
		perror("connect");
		exit(EXIT_FAILURE);
	}

	tv.tv_usec = 0;
	if (setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
		perror("setsockopt, SO_RCVTIMEO reset");
	if (setsockopt(s, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)))
		perror("setsockopt, SO_SNDTIMEO reset");

	fprintf(stderr, "Connected to %s\n", addr.sun_path);

	if (dup2(s, (int)fd) < 0) {
		perror("dup");
		exit(EXIT_FAILURE);
	}

	close(s);

	if (qemu_argc) {
		char **name;

		for (name = qemu_names; *name; name++) {
			qemu_argv[0] = *name;
			execvp(*name, qemu_argv);
			if (errno != ENOENT) {
				perror("execvp");
				usage(argv[0]);
			}
		}
		if (errno == ENOENT)
			fprintf(stderr, "Couldn't find qemu command\n");
	} else {
		execvp(argv[2], argv + 2);
	}

	perror("execvp");

	return EXIT_FAILURE;
}