// 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
 *
 * migrate.c - Migration sections, layout, and routines
 *
 * Copyright (c) 2025 Red Hat GmbH
 * Author: Stefano Brivio <sbrivio@redhat.com>
 */

#include <errno.h>
#include <sys/uio.h>

#include "util.h"
#include "ip.h"
#include "passt.h"
#include "inany.h"
#include "flow.h"
#include "flow_table.h"

#include "migrate.h"

/* Current version of migration data */
#define MIGRATE_VERSION		1

/* Magic as we see it and as seen with reverse endianness */
#define MIGRATE_MAGIC		0xB1BB1D1B0BB1D1B0
#define MIGRATE_MAGIC_SWAPPED	0xB0D1B1B01B1DBBB1

/* Migration header to send from source */
static union migrate_header header = {
	.magic		= MIGRATE_MAGIC,
	.version	= htonl_constant(MIGRATE_VERSION),
	.time_t_size	= htonl_constant(sizeof(time_t)),
	.flow_size	= htonl_constant(sizeof(union flow)),
	.flow_sidx_size	= htonl_constant(sizeof(struct flow_sidx)),
	.voidp_size	= htonl_constant(sizeof(void *)),
};

/* Data sections for version 1 */
static struct iovec sections_v1[] = {
	{ &header,	sizeof(header) },
};

/* Set of data versions */
static struct migrate_data data_versions[] = {
	{
		1,	sections_v1,
	},
	{ 0 },
};

/* Handlers to call in source before sending data */
struct migrate_handler handlers_source_pre[] = {
	{ flow_migrate_source_pre },
	{ 0 },
};

/* Handlers to call in source after sending data */
struct migrate_handler handlers_source_post[] = {
	{ 0 },
};

/* Handlers to call in target before receiving data with version 1 */
struct migrate_handler handlers_target_pre_v1[] = {
	{ 0 },
};

/* Handlers to call in target after receiving data with version 1 */
struct migrate_handler handlers_target_post_v1[] = {
	{ 0 },
};

/* Versioned sets of migration handlers */
struct migrate_target_handlers target_handlers[] = {
	{
		1,
		handlers_target_pre_v1,
		handlers_target_post_v1,
	},
	{ 0 },
};

/**
 * migrate_source_pre() - Pre-migration tasks as source
 * @c:		Execution context
 * @m:		Migration metadata
 *
 * Return: 0 on success, error code on failure
 */
static int migrate_source_pre(struct ctx *c, struct migrate_meta *m)
{
	struct migrate_handler *h;

	for (h = handlers_source_pre; h->fn; h++) {
		int rc;

		if ((rc = h->fn(c, m)))
			return rc;
	}

	return 0;
}

/**
 * migrate_source_state() - Send device state as migration source
 * @fd:		Descriptor for state transfer
 * @m:		Migration metadata
 *
 * Return: 0 on success, error code on failure
 */
static int migrate_source_state(int fd, const struct migrate_meta *m)
{
	static struct migrate_data *d;
	int count, rc;

	(void)m;

	for (d = data_versions; d->v != MIGRATE_VERSION; d++);

	for (count = 0; d->sections[count].iov_len; count++);

	debug("Writing %u migration sections", count - 1 /* minus header */);
	rc = write_remainder(fd, d->sections, count, 0);
	if (rc < 0)
		return errno;

	return 0;
}

/**
 * migrate_source_post() - Post-migration tasks as source
 * @c:		Execution context
 * @m:		Migration metadata
 *
 * Return: 0 on success, error code on failure
 */
static void migrate_source_post(struct ctx *c, struct migrate_meta *m)
{
	struct migrate_handler *h;

	for (h = handlers_source_post; h->fn; h++)
		h->fn(c, m);
}

/**
 * migrate_source() - Migration as source, send state to hypervisor
 * @c:		Execution context
 * @fd:		File descriptor for state transfer
 *
 * Return: 0 on success, positive error code on failure
 */
int migrate_source(struct ctx *c, int fd)
{
	struct migrate_meta m;
	int rc;

	if ((rc = migrate_source_pre(c, &m))) {
		err("Source pre-migration failed: %s, abort", strerror_(rc));
		return rc;
	}

	debug("Saving backend state");

	rc = migrate_source_state(fd, &m);
	if (rc)
		err("Source migration failed: %s", strerror_(rc));
	else
		migrate_source_post(c, &m);

	return rc;
}

/**
 * migrate_target_read_header() - Set metadata in target from source header
 * @fd:		Descriptor for state transfer
 * @m:		Migration metadata, filled on return
 *
 * Return: 0 on success, error code on failure
 */
static int migrate_target_read_header(int fd, struct migrate_meta *m)
{
	static struct migrate_data *d;
	union migrate_header h;

	if (read_all_buf(fd, &h, sizeof(h)))
		return errno;

	debug("Source magic: 0x%016" PRIx64 ", sizeof(void *): %u, version: %u",
	      h.magic, ntohl(h.voidp_size), ntohl(h.version));

	for (d = data_versions; d->v != ntohl(h.version) && d->v; d++);
	if (!d->v)
		return ENOTSUP;
	m->v = d->v;

	if (h.magic == MIGRATE_MAGIC)
		m->bswap = false;
	else if (h.magic == MIGRATE_MAGIC_SWAPPED)
		m->bswap = true;
	else
		return ENOTSUP;

	if (ntohl(h.voidp_size) == 4)
		m->source_64b = false;
	else if (ntohl(h.voidp_size) == 8)
		m->source_64b = true;
	else
		return ENOTSUP;

	if (ntohl(h.time_t_size) == 4)
		m->time_64b = false;
	else if (ntohl(h.time_t_size) == 8)
		m->time_64b = true;
	else
		return ENOTSUP;

	m->flow_size = ntohl(h.flow_size);
	m->flow_sidx_size = ntohl(h.flow_sidx_size);

	return 0;
}

/**
 * migrate_target_pre() - Pre-migration tasks as target
 * @c:		Execution context
 * @m:		Migration metadata
 *
 * Return: 0 on success, error code on failure
 */
static int migrate_target_pre(struct ctx *c, struct migrate_meta *m)
{
	struct migrate_target_handlers *th;
	struct migrate_handler *h;

	for (th = target_handlers; th->v != m->v && th->v; th++);

	for (h = th->pre; h->fn; h++) {
		int rc;

		if ((rc = h->fn(c, m)))
			return rc;
	}

	return 0;
}

/**
 * migrate_target_state() - Receive device state as migration target
 * @fd:		Descriptor for state transfer
 * @m:		Migration metadata
 *
 * Return: 0 on success, error code on failure
 *
 * #syscalls:vu readv
 */
static int migrate_target_state(int fd, const struct migrate_meta *m)
{
	static struct migrate_data *d;
	unsigned cnt;
	int rc;

	for (d = data_versions; d->v != m->v && d->v; d++);

	for (cnt = 0; d->sections[cnt + 1 /* skip header */].iov_len; cnt++);

	debug("Reading %u migration sections", cnt);
	rc = read_remainder(fd, d->sections + 1, cnt, 0);
	if (rc < 0)
		return errno;

	return 0;
}

/**
 * migrate_target_post() - Post-migration tasks as target
 * @c:		Execution context
 * @m:		Migration metadata
 */
static void migrate_target_post(struct ctx *c, struct migrate_meta *m)
{
	struct migrate_target_handlers *th;
	struct migrate_handler *h;

	for (th = target_handlers; th->v != m->v && th->v; th++);

	for (h = th->post; h->fn; h++)
		h->fn(c, m);
}

/**
 * migrate_target() - Migration as target, receive state from hypervisor
 * @c:		Execution context
 * @fd:		File descriptor for state transfer
 *
 * Return: 0 on success, positive error code on failure
 */
int migrate_target(struct ctx *c, int fd)
{
	struct migrate_meta m;
	int rc;

	rc = migrate_target_read_header(fd, &m);
	if (rc) {
		err("Migration header check failed: %s, abort", strerror_(rc));
		return rc;
	}

	if ((rc = migrate_target_pre(c, &m))) {
		err("Target pre-migration failed: %s, abort", strerror_(rc));
		return rc;
	}

	debug("Loading backend state");

	rc = migrate_target_state(fd, &m);
	if (rc)
		err("Target migration failed: %s", strerror_(rc));
	else
		migrate_target_post(c, &m);

	return rc;
}