migration/migration.c

/*
 * QEMU live migration
 *
 * Copyright IBM, Corp. 2008
 *
 * Authors:
 *  Anthony Liguori   <aliguori@us.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 * Contributions after 2012-01-13 are licensed under the terms of the
 * GNU GPL, version 2 or (at your option) any later version.
 */

#include "qemu/osdep.h"
#include "qemu/cutils.h"
#include "qemu/error-report.h"
#include "qemu/main-loop.h"
#include "migration/blocker.h"
#include "exec.h"
#include "fd.h"
#include "socket.h"
#include "rdma.h"
#include "ram.h"
#include "migration/migration.h"
#include "savevm.h"
#include "qemu-file-channel.h"
#include "qemu-file.h"
#include "migration/vmstate.h"
#include "sysemu/sysemu.h"
#include "block/block.h"
#include "qapi/qmp/qerror.h"
#include "qapi/util.h"
#include "qemu/sockets.h"
#include "qemu/rcu.h"
#include "block.h"
#include "postcopy-ram.h"
#include "qemu/thread.h"
#include "qmp-commands.h"
#include "trace.h"
#include "qapi-event.h"
#include "qom/cpu.h"
#include "exec/memory.h"
#include "exec/address-spaces.h"
#include "exec/target_page.h"
#include "io/channel-buffer.h"
#include "migration/colo.h"

#define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */

/* Amount of time to allocate to each "chunk" of bandwidth-throttled
 * data. */
#define BUFFER_DELAY     100
#define XFER_LIMIT_RATIO (1000 / BUFFER_DELAY)

/* Time in milliseconds we are allowed to stop the source,
 * for sending the last part */
#define DEFAULT_MIGRATE_SET_DOWNTIME 300

/* Maximum migrate downtime set to 2000 seconds */
#define MAX_MIGRATE_DOWNTIME_SECONDS 2000
#define MAX_MIGRATE_DOWNTIME (MAX_MIGRATE_DOWNTIME_SECONDS * 1000)

/* Default compression thread count */
#define DEFAULT_MIGRATE_COMPRESS_THREAD_COUNT 8
/* Default decompression thread count, usually decompression is at
 * least 4 times as fast as compression.*/
#define DEFAULT_MIGRATE_DECOMPRESS_THREAD_COUNT 2
/*0: means nocompress, 1: best speed, ... 9: best compress ratio */
#define DEFAULT_MIGRATE_COMPRESS_LEVEL 1
/* Define default autoconverge cpu throttle migration parameters */
#define DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL 20
#define DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT 10

/* Migration XBZRLE default cache size */
#define DEFAULT_MIGRATE_CACHE_SIZE (64 * 1024 * 1024)

/* The delay time (in ms) between two COLO checkpoints
 * Note: Please change this default value to 10000 when we support hybrid mode.
 */
#define DEFAULT_MIGRATE_X_CHECKPOINT_DELAY 200

static NotifierList migration_state_notifiers =
    NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);

static bool deferred_incoming;

/* When we add fault tolerance, we could have several
   migrations at once.  For now we don't need to add
   dynamic creation of migration */

/* For outgoing */
MigrationState *migrate_get_current(void)
{
    static bool once;
    static MigrationState current_migration = {
        .state = MIGRATION_STATUS_NONE,
        .xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE,
        .mbps = -1,
        .parameters = {
            .compress_level = DEFAULT_MIGRATE_COMPRESS_LEVEL,
            .compress_threads = DEFAULT_MIGRATE_COMPRESS_THREAD_COUNT,
            .decompress_threads = DEFAULT_MIGRATE_DECOMPRESS_THREAD_COUNT,
            .cpu_throttle_initial = DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL,
            .cpu_throttle_increment = DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT,
            .max_bandwidth = MAX_THROTTLE,
            .downtime_limit = DEFAULT_MIGRATE_SET_DOWNTIME,
            .x_checkpoint_delay = DEFAULT_MIGRATE_X_CHECKPOINT_DELAY,
        },
    };

    if (!once) {
        current_migration.parameters.tls_creds = g_strdup("");
        current_migration.parameters.tls_hostname = g_strdup("");
        once = true;
    }
    return &current_migration;
}

MigrationIncomingState *migration_incoming_get_current(void)
{
    static bool once;
    static MigrationIncomingState mis_current;

    if (!once) {
        mis_current.state = MIGRATION_STATUS_NONE;
        memset(&mis_current, 0, sizeof(MigrationIncomingState));
        qemu_mutex_init(&mis_current.rp_mutex);
        qemu_event_init(&mis_current.main_thread_load_event, false);
        once = true;
    }
    return &mis_current;
}

void migration_incoming_state_destroy(void)
{
    struct MigrationIncomingState *mis = migration_incoming_get_current();

    if (mis->to_src_file) {
        /* Tell source that we are done */
        migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0);
        qemu_fclose(mis->to_src_file);
        mis->to_src_file = NULL;
    }

    if (mis->from_src_file) {
        qemu_fclose(mis->from_src_file);
        mis->from_src_file = NULL;
    }

    qemu_event_destroy(&mis->main_thread_load_event);
}


typedef struct {
    bool optional;
    uint32_t size;
    uint8_t runstate[100];
    RunState state;
    bool received;
} GlobalState;

static GlobalState global_state;

int global_state_store(void)
{
    if (!runstate_store((char *)global_state.runstate,
                        sizeof(global_state.runstate))) {
        error_report("runstate name too big: %s", global_state.runstate);
        trace_migrate_state_too_big();
        return -EINVAL;
    }
    return 0;
}

void global_state_store_running(void)
{
    const char *state = RunState_lookup[RUN_STATE_RUNNING];
    strncpy((char *)global_state.runstate,
           state, sizeof(global_state.runstate));
}

static bool global_state_received(void)
{
    return global_state.received;
}

static RunState global_state_get_runstate(void)
{
    return global_state.state;
}

void global_state_set_optional(void)
{
    global_state.optional = true;
}

static bool global_state_needed(void *opaque)
{
    GlobalState *s = opaque;
    char *runstate = (char *)s->runstate;

    /* If it is not optional, it is mandatory */

    if (s->optional == false) {
        return true;
    }

    /* If state is running or paused, it is not needed */

    if (strcmp(runstate, "running") == 0 ||
        strcmp(runstate, "paused") == 0) {
        return false;
    }

    /* for any other state it is needed */
    return true;
}

static int global_state_post_load(void *opaque, int version_id)
{
    GlobalState *s = opaque;
    Error *local_err = NULL;
    int r;
    char *runstate = (char *)s->runstate;

    s->received = true;
    trace_migrate_global_state_post_load(runstate);

    r = qapi_enum_parse(RunState_lookup, runstate, RUN_STATE__MAX,
                                -1, &local_err);

    if (r == -1) {
        if (local_err) {
            error_report_err(local_err);
        }
        return -EINVAL;
    }
    s->state = r;

    return 0;
}

static void global_state_pre_save(void *opaque)
{
    GlobalState *s = opaque;

    trace_migrate_global_state_pre_save((char *)s->runstate);
    s->size = strlen((char *)s->runstate) + 1;
}

static const VMStateDescription vmstate_globalstate = {
    .name = "globalstate",
    .version_id = 1,
    .minimum_version_id = 1,
    .post_load = global_state_post_load,
    .pre_save = global_state_pre_save,
    .needed = global_state_needed,
    .fields = (VMStateField[]) {
        VMSTATE_UINT32(size, GlobalState),
        VMSTATE_BUFFER(runstate, GlobalState),
        VMSTATE_END_OF_LIST()
    },
};

void register_global_state(void)
{
    /* We would use it independently that we receive it */
    strcpy((char *)&global_state.runstate, "");
    global_state.received = false;
    vmstate_register(NULL, 0, &vmstate_globalstate, &global_state);
}

static void migrate_generate_event(int new_state)
{
    if (migrate_use_events()) {
        qapi_event_send_migration(new_state, &error_abort);
    }
}

/*
 * Called on -incoming with a defer: uri.
 * The migration can be started later after any parameters have been
 * changed.
 */
static void deferred_incoming_migration(Error **errp)
{
    if (deferred_incoming) {
        error_setg(errp, "Incoming migration already deferred");
    }
    deferred_incoming = true;
}

/* Request a range of pages from the source VM at the given
 * start address.
 *   rbname: Name of the RAMBlock to request the page in, if NULL it's the same
 *           as the last request (a name must have been given previously)
 *   Start: Address offset within the RB
 *   Len: Length in bytes required - must be a multiple of pagesize
 */
void migrate_send_rp_req_pages(MigrationIncomingState *mis, const char *rbname,
                               ram_addr_t start, size_t len)
{
    uint8_t bufc[12 + 1 + 255]; /* start (8), len (4), rbname up to 256 */
    size_t msglen = 12; /* start + len */

    *(uint64_t *)bufc = cpu_to_be64((uint64_t)start);
    *(uint32_t *)(bufc + 8) = cpu_to_be32((uint32_t)len);

    if (rbname) {
        int rbname_len = strlen(rbname);
        assert(rbname_len < 256);

        bufc[msglen++] = rbname_len;
        memcpy(bufc + msglen, rbname, rbname_len);
        msglen += rbname_len;
        migrate_send_rp_message(mis, MIG_RP_MSG_REQ_PAGES_ID, msglen, bufc);
    } else {
        migrate_send_rp_message(mis, MIG_RP_MSG_REQ_PAGES, msglen, bufc);
    }
}

void qemu_start_incoming_migration(const char *uri, Error **errp)
{
    const char *p;

    qapi_event_send_migration(MIGRATION_STATUS_SETUP, &error_abort);
    if (!strcmp(uri, "defer")) {
        deferred_incoming_migration(errp);
    } else if (strstart(uri, "tcp:", &p)) {
        tcp_start_incoming_migration(p, errp);
#ifdef CONFIG_RDMA
    } else if (strstart(uri, "rdma:", &p)) {
        rdma_start_incoming_migration(p, errp);
#endif
    } else if (strstart(uri, "exec:", &p)) {
        exec_start_incoming_migration(p, errp);
    } else if (strstart(uri, "unix:", &p)) {
        unix_start_incoming_migration(p, errp);
    } else if (strstart(uri, "fd:", &p)) {
        fd_start_incoming_migration(p, errp);
    } else {
        error_setg(errp, "unknown migration protocol: %s", uri);
    }
}

static void process_incoming_migration_bh(void *opaque)
{
    Error *local_err = NULL;
    MigrationIncomingState *mis = opaque;

    /* Make sure all file formats flush their mutable metadata.
     * If we get an error here, just don't restart the VM yet. */
    bdrv_invalidate_cache_all(&local_err);
    if (local_err) {
        error_report_err(local_err);
        local_err = NULL;
        autostart = false;
    }

    /*
     * This must happen after all error conditions are dealt with and
     * we're sure the VM is going to be running on this host.
     */
    qemu_announce_self();

    /* If global state section was not received or we are in running
       state, we need to obey autostart. Any other state is set with
       runstate_set. */

    if (!global_state_received() ||
        global_state_get_runstate() == RUN_STATE_RUNNING) {
        if (autostart) {
            vm_start();
        } else {
            runstate_set(RUN_STATE_PAUSED);
        }
    } else {
        runstate_set(global_state_get_runstate());
    }
    migrate_decompress_threads_join();
    /*
     * This must happen after any state changes since as soon as an external
     * observer sees this event they might start to prod at the VM assuming
     * it's ready to use.
     */
    migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                      MIGRATION_STATUS_COMPLETED);
    qemu_bh_delete(mis->bh);
    migration_incoming_state_destroy();
}

static void process_incoming_migration_co(void *opaque)
{
    QEMUFile *f = opaque;
    MigrationIncomingState *mis = migration_incoming_get_current();
    PostcopyState ps;
    int ret;

    mis->from_src_file = f;
    mis->largest_page_size = qemu_ram_pagesize_largest();
    postcopy_state_set(POSTCOPY_INCOMING_NONE);
    migrate_set_state(&mis->state, MIGRATION_STATUS_NONE,
                      MIGRATION_STATUS_ACTIVE);
    ret = qemu_loadvm_state(f);

    ps = postcopy_state_get();
    trace_process_incoming_migration_co_end(ret, ps);
    if (ps != POSTCOPY_INCOMING_NONE) {
        if (ps == POSTCOPY_INCOMING_ADVISE) {
            /*
             * Where a migration had postcopy enabled (and thus went to advise)
             * but managed to complete within the precopy period, we can use
             * the normal exit.
             */
            postcopy_ram_incoming_cleanup(mis);
        } else if (ret >= 0) {
            /*
             * Postcopy was started, cleanup should happen at the end of the
             * postcopy thread.
             */
            trace_process_incoming_migration_co_postcopy_end_main();
            return;
        }
        /* Else if something went wrong then just fall out of the normal exit */
    }

    /* we get COLO info, and know if we are in COLO mode */
    if (!ret && migration_incoming_enable_colo()) {
        mis->migration_incoming_co = qemu_coroutine_self();
        qemu_thread_create(&mis->colo_incoming_thread, "COLO incoming",
             colo_process_incoming_thread, mis, QEMU_THREAD_JOINABLE);
        mis->have_colo_incoming_thread = true;
        qemu_coroutine_yield();

        /* Wait checkpoint incoming thread exit before free resource */
        qemu_thread_join(&mis->colo_incoming_thread);
    }

    if (ret < 0) {
        migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                          MIGRATION_STATUS_FAILED);
        error_report("load of migration failed: %s", strerror(-ret));
        migrate_decompress_threads_join();
        exit(EXIT_FAILURE);
    }

    free_xbzrle_decoded_buf();

    mis->bh = qemu_bh_new(process_incoming_migration_bh, mis);
    qemu_bh_schedule(mis->bh);
}

void migration_fd_process_incoming(QEMUFile *f)
{
    Coroutine *co = qemu_coroutine_create(process_incoming_migration_co, f);

    migrate_decompress_threads_create();
    qemu_file_set_blocking(f, false);
    qemu_coroutine_enter(co);
}

/*
 * Send a message on the return channel back to the source
 * of the migration.
 */
void migrate_send_rp_message(MigrationIncomingState *mis,
                             enum mig_rp_message_type message_type,
                             uint16_t len, void *data)
{
    trace_migrate_send_rp_message((int)message_type, len);
    qemu_mutex_lock(&mis->rp_mutex);
    qemu_put_be16(mis->to_src_file, (unsigned int)message_type);
    qemu_put_be16(mis->to_src_file, len);
    qemu_put_buffer(mis->to_src_file, data, len);
    qemu_fflush(mis->to_src_file);
    qemu_mutex_unlock(&mis->rp_mutex);
}

/*
 * Send a 'SHUT' message on the return channel with the given value
 * to indicate that we've finished with the RP.  Non-0 value indicates
 * error.
 */
void migrate_send_rp_shut(MigrationIncomingState *mis,
                          uint32_t value)
{
    uint32_t buf;

    buf = cpu_to_be32(value);
    migrate_send_rp_message(mis, MIG_RP_MSG_SHUT, sizeof(buf), &buf);
}

/*
 * Send a 'PONG' message on the return channel with the given value
 * (normally in response to a 'PING')
 */
void migrate_send_rp_pong(MigrationIncomingState *mis,
                          uint32_t value)
{
    uint32_t buf;

    buf = cpu_to_be32(value);
    migrate_send_rp_message(mis, MIG_RP_MSG_PONG, sizeof(buf), &buf);
}

MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
{
    MigrationCapabilityStatusList *head = NULL;
    MigrationCapabilityStatusList *caps;
    MigrationState *s = migrate_get_current();
    int i;

    caps = NULL; /* silence compiler warning */
    for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
#ifndef CONFIG_LIVE_BLOCK_MIGRATION
        if (i == MIGRATION_CAPABILITY_BLOCK) {
            continue;
        }
#endif
        if (i == MIGRATION_CAPABILITY_X_COLO && !colo_supported()) {
            continue;
        }
        if (head == NULL) {
            head = g_malloc0(sizeof(*caps));
            caps = head;
        } else {
            caps->next = g_malloc0(sizeof(*caps));
            caps = caps->next;
        }
        caps->value =
            g_malloc(sizeof(*caps->value));
        caps->value->capability = i;
        caps->value->state = s->enabled_capabilities[i];
    }

    return head;
}

MigrationParameters *qmp_query_migrate_parameters(Error **errp)
{
    MigrationParameters *params;
    MigrationState *s = migrate_get_current();

    params = g_malloc0(sizeof(*params));
    params->has_compress_level = true;
    params->compress_level = s->parameters.compress_level;
    params->has_compress_threads = true;
    params->compress_threads = s->parameters.compress_threads;
    params->has_decompress_threads = true;
    params->decompress_threads = s->parameters.decompress_threads;
    params->has_cpu_throttle_initial = true;
    params->cpu_throttle_initial = s->parameters.cpu_throttle_initial;
    params->has_cpu_throttle_increment = true;
    params->cpu_throttle_increment = s->parameters.cpu_throttle_increment;
    params->has_tls_creds = !!s->parameters.tls_creds;
    params->tls_creds = g_strdup(s->parameters.tls_creds);
    params->has_tls_hostname = !!s->parameters.tls_hostname;
    params->tls_hostname = g_strdup(s->parameters.tls_hostname);
    params->has_max_bandwidth = true;
    params->max_bandwidth = s->parameters.max_bandwidth;
    params->has_downtime_limit = true;
    params->downtime_limit = s->parameters.downtime_limit;
    params->has_x_checkpoint_delay = true;
    params->x_checkpoint_delay = s->parameters.x_checkpoint_delay;
    params->has_block_incremental = true;
    params->block_incremental = s->parameters.block_incremental;

    return params;
}

/*
 * Return true if we're already in the middle of a migration
 * (i.e. any of the active or setup states)
 */
static bool migration_is_setup_or_active(int state)
{
    switch (state) {
    case MIGRATION_STATUS_ACTIVE:
    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
    case MIGRATION_STATUS_SETUP:
        return true;

    default:
        return false;

    }
}

static void populate_ram_info(MigrationInfo *info, MigrationState *s)
{
    info->has_ram = true;
    info->ram = g_malloc0(sizeof(*info->ram));
    info->ram->transferred = ram_counters.transferred;
    info->ram->total = ram_bytes_total();
    info->ram->duplicate = ram_counters.duplicate;
    /* legacy value.  It is not used anymore */
    info->ram->skipped = 0;
    info->ram->normal = ram_counters.normal;
    info->ram->normal_bytes = ram_counters.normal *
        qemu_target_page_size();
    info->ram->mbps = s->mbps;
    info->ram->dirty_sync_count = ram_counters.dirty_sync_count;
    info->ram->postcopy_requests = ram_counters.postcopy_requests;
    info->ram->page_size = qemu_target_page_size();

    if (migrate_use_xbzrle()) {
        info->has_xbzrle_cache = true;
        info->xbzrle_cache = g_malloc0(sizeof(*info->xbzrle_cache));
        info->xbzrle_cache->cache_size = migrate_xbzrle_cache_size();
        info->xbzrle_cache->bytes = xbzrle_counters.bytes;
        info->xbzrle_cache->pages = xbzrle_counters.pages;
        info->xbzrle_cache->cache_miss = xbzrle_counters.cache_miss;
        info->xbzrle_cache->cache_miss_rate = xbzrle_counters.cache_miss_rate;
        info->xbzrle_cache->overflow = xbzrle_counters.overflow;
    }

    if (cpu_throttle_active()) {
        info->has_cpu_throttle_percentage = true;
        info->cpu_throttle_percentage = cpu_throttle_get_percentage();
    }

    if (s->state != MIGRATION_STATUS_COMPLETED) {
        info->ram->remaining = ram_bytes_remaining();
        info->ram->dirty_pages_rate = ram_counters.dirty_pages_rate;
    }
}

static void populate_disk_info(MigrationInfo *info)
{
    if (blk_mig_active()) {
        info->has_disk = true;
        info->disk = g_malloc0(sizeof(*info->disk));
        info->disk->transferred = blk_mig_bytes_transferred();
        info->disk->remaining = blk_mig_bytes_remaining();
        info->disk->total = blk_mig_bytes_total();
    }
}

MigrationInfo *qmp_query_migrate(Error **errp)
{
    MigrationInfo *info = g_malloc0(sizeof(*info));
    MigrationState *s = migrate_get_current();

    switch (s->state) {
    case MIGRATION_STATUS_NONE:
        /* no migration has happened ever */
        break;
    case MIGRATION_STATUS_SETUP:
        info->has_status = true;
        info->has_total_time = false;
        break;
    case MIGRATION_STATUS_ACTIVE:
    case MIGRATION_STATUS_CANCELLING:
    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
         /* TODO add some postcopy stats */
        info->has_status = true;
        info->has_total_time = true;
        info->total_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME)
            - s->total_time;
        info->has_expected_downtime = true;
        info->expected_downtime = s->expected_downtime;
        info->has_setup_time = true;
        info->setup_time = s->setup_time;

        populate_ram_info(info, s);
        populate_disk_info(info);
        break;
    case MIGRATION_STATUS_COLO:
        info->has_status = true;
        /* TODO: display COLO specific information (checkpoint info etc.) */
        break;
    case MIGRATION_STATUS_COMPLETED:
        info->has_status = true;
        info->has_total_time = true;
        info->total_time = s->total_time;
        info->has_downtime = true;
        info->downtime = s->downtime;
        info->has_setup_time = true;
        info->setup_time = s->setup_time;

        populate_ram_info(info, s);
        break;
    case MIGRATION_STATUS_FAILED:
        info->has_status = true;
        if (s->error) {
            info->has_error_desc = true;
            info->error_desc = g_strdup(error_get_pretty(s->error));
        }
        break;
    case MIGRATION_STATUS_CANCELLED:
        info->has_status = true;
        break;
    }
    info->status = s->state;

    return info;
}

void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
                                  Error **errp)
{
    MigrationState *s = migrate_get_current();
    MigrationCapabilityStatusList *cap;
    bool old_postcopy_cap = migrate_postcopy_ram();

    if (migration_is_setup_or_active(s->state)) {
        error_setg(errp, QERR_MIGRATION_ACTIVE);
        return;
    }

    for (cap = params; cap; cap = cap->next) {
#ifndef CONFIG_LIVE_BLOCK_MIGRATION
        if (cap->value->capability == MIGRATION_CAPABILITY_BLOCK
            && cap->value->state) {
            error_setg(errp, "QEMU compiled without old-style (blk/-b, inc/-i) "
                       "block migration");
            error_append_hint(errp, "Use drive_mirror+NBD instead.\n");
            continue;
        }
#endif
        if (cap->value->capability == MIGRATION_CAPABILITY_X_COLO) {
            if (!colo_supported()) {
                error_setg(errp, "COLO is not currently supported, please"
                             " configure with --enable-colo option in order to"
                             " support COLO feature");
                continue;
            }
        }
        s->enabled_capabilities[cap->value->capability] = cap->value->state;
    }

    if (migrate_postcopy_ram()) {
        if (migrate_use_compression()) {
            /* The decompression threads asynchronously write into RAM
             * rather than use the atomic copies needed to avoid
             * userfaulting.  It should be possible to fix the decompression
             * threads for compatibility in future.
             */
            error_report("Postcopy is not currently compatible with "
                         "compression");
            s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM] =
                false;
        }
        /* This check is reasonably expensive, so only when it's being
         * set the first time, also it's only the destination that needs
         * special support.
         */
        if (!old_postcopy_cap && runstate_check(RUN_STATE_INMIGRATE) &&
            !postcopy_ram_supported_by_host()) {
            /* postcopy_ram_supported_by_host will have emitted a more
             * detailed message
             */
            error_report("Postcopy is not supported");
            s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM] =
                false;
        }
    }
}

void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
{
    MigrationState *s = migrate_get_current();

    if (params->has_compress_level &&
        (params->compress_level < 0 || params->compress_level > 9)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "compress_level",
                   "is invalid, it should be in the range of 0 to 9");
        return;
    }
    if (params->has_compress_threads &&
        (params->compress_threads < 1 || params->compress_threads > 255)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "compress_threads",
                   "is invalid, it should be in the range of 1 to 255");
        return;
    }
    if (params->has_decompress_threads &&
        (params->decompress_threads < 1 || params->decompress_threads > 255)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "decompress_threads",
                   "is invalid, it should be in the range of 1 to 255");
        return;
    }
    if (params->has_cpu_throttle_initial &&
        (params->cpu_throttle_initial < 1 ||
         params->cpu_throttle_initial > 99)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "cpu_throttle_initial",
                   "an integer in the range of 1 to 99");
        return;
    }
    if (params->has_cpu_throttle_increment &&
        (params->cpu_throttle_increment < 1 ||
         params->cpu_throttle_increment > 99)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "cpu_throttle_increment",
                   "an integer in the range of 1 to 99");
        return;
    }
    if (params->has_max_bandwidth &&
        (params->max_bandwidth < 0 || params->max_bandwidth > SIZE_MAX)) {
        error_setg(errp, "Parameter 'max_bandwidth' expects an integer in the"
                         " range of 0 to %zu bytes/second", SIZE_MAX);
        return;
    }
    if (params->has_downtime_limit &&
        (params->downtime_limit < 0 ||
         params->downtime_limit > MAX_MIGRATE_DOWNTIME)) {
        error_setg(errp, "Parameter 'downtime_limit' expects an integer in "
                         "the range of 0 to %d milliseconds",
                         MAX_MIGRATE_DOWNTIME);
        return;
    }
    if (params->has_x_checkpoint_delay && (params->x_checkpoint_delay < 0)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                    "x_checkpoint_delay",
                    "is invalid, it should be positive");
    }

    if (params->has_compress_level) {
        s->parameters.compress_level = params->compress_level;
    }
    if (params->has_compress_threads) {
        s->parameters.compress_threads = params->compress_threads;
    }
    if (params->has_decompress_threads) {
        s->parameters.decompress_threads = params->decompress_threads;
    }
    if (params->has_cpu_throttle_initial) {
        s->parameters.cpu_throttle_initial = params->cpu_throttle_initial;
    }
    if (params->has_cpu_throttle_increment) {
        s->parameters.cpu_throttle_increment = params->cpu_throttle_increment;
    }
    if (params->has_tls_creds) {
        g_free(s->parameters.tls_creds);
        s->parameters.tls_creds = g_strdup(params->tls_creds);
    }
    if (params->has_tls_hostname) {
        g_free(s->parameters.tls_hostname);
        s->parameters.tls_hostname = g_strdup(params->tls_hostname);
    }
    if (params->has_max_bandwidth) {
        s->parameters.max_bandwidth = params->max_bandwidth;
        if (s->to_dst_file) {
            qemu_file_set_rate_limit(s->to_dst_file,
                                s->parameters.max_bandwidth / XFER_LIMIT_RATIO);
        }
    }
    if (params->has_downtime_limit) {
        s->parameters.downtime_limit = params->downtime_limit;
    }

    if (params->has_x_checkpoint_delay) {
        s->parameters.x_checkpoint_delay = params->x_checkpoint_delay;
        if (migration_in_colo_state()) {
            colo_checkpoint_notify(s);
        }
    }
    if (params->has_block_incremental) {
        s->parameters.block_incremental = params->block_incremental;
    }
}


void qmp_migrate_start_postcopy(Error **errp)
{
    MigrationState *s = migrate_get_current();

    if (!migrate_postcopy_ram()) {
        error_setg(errp, "Enable postcopy with migrate_set_capability before"
                         " the start of migration");
        return;
    }

    if (s->state == MIGRATION_STATUS_NONE) {
        error_setg(errp, "Postcopy must be started after migration has been"
                         " started");
        return;
    }
    /*
     * we don't error if migration has finished since that would be racy
     * with issuing this command.
     */
    atomic_set(&s->start_postcopy, true);
}

/* shared migration helpers */

void migrate_set_state(int *state, int old_state, int new_state)
{
    if (atomic_cmpxchg(state, old_state, new_state) == old_state) {
        trace_migrate_set_state(new_state);
        migrate_generate_event(new_state);
    }
}

void migrate_set_block_enabled(bool value, Error **errp)
{
    MigrationCapabilityStatusList *cap;

    cap = g_new0(MigrationCapabilityStatusList, 1);
    cap->value = g_new0(MigrationCapabilityStatus, 1);
    cap->value->capability = MIGRATION_CAPABILITY_BLOCK;
    cap->value->state = value;
    qmp_migrate_set_capabilities(cap, errp);
    qapi_free_MigrationCapabilityStatusList(cap);
}

static void migrate_set_block_incremental(MigrationState *s, bool value)
{
    s->parameters.block_incremental = value;
}

static void block_cleanup_parameters(MigrationState *s)
{
    if (s->must_remove_block_options) {
        /* setting to false can never fail */
        migrate_set_block_enabled(false, &error_abort);
        migrate_set_block_incremental(s, false);
        s->must_remove_block_options = false;
    }
}

static void migrate_fd_cleanup(void *opaque)
{
    MigrationState *s = opaque;

    qemu_bh_delete(s->cleanup_bh);
    s->cleanup_bh = NULL;

    if (s->to_dst_file) {
        trace_migrate_fd_cleanup();
        qemu_mutex_unlock_iothread();
        if (s->migration_thread_running) {
            qemu_thread_join(&s->thread);
            s->migration_thread_running = false;
        }
        qemu_mutex_lock_iothread();

        migrate_compress_threads_join();
        qemu_fclose(s->to_dst_file);
        s->to_dst_file = NULL;
    }

    assert((s->state != MIGRATION_STATUS_ACTIVE) &&
           (s->state != MIGRATION_STATUS_POSTCOPY_ACTIVE));

    if (s->state == MIGRATION_STATUS_CANCELLING) {
        migrate_set_state(&s->state, MIGRATION_STATUS_CANCELLING,
                          MIGRATION_STATUS_CANCELLED);
    }

    notifier_list_notify(&migration_state_notifiers, s);
    block_cleanup_parameters(s);
}

void migrate_fd_error(MigrationState *s, const Error *error)
{
    trace_migrate_fd_error(error_get_pretty(error));
    assert(s->to_dst_file == NULL);
    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                      MIGRATION_STATUS_FAILED);
    if (!s->error) {
        s->error = error_copy(error);
    }
    notifier_list_notify(&migration_state_notifiers, s);
    block_cleanup_parameters(s);
}

static void migrate_fd_cancel(MigrationState *s)
{
    int old_state ;
    QEMUFile *f = migrate_get_current()->to_dst_file;
    trace_migrate_fd_cancel();

    if (s->rp_state.from_dst_file) {
        /* shutdown the rp socket, so causing the rp thread to shutdown */
        qemu_file_shutdown(s->rp_state.from_dst_file);
    }

    do {
        old_state = s->state;
        if (!migration_is_setup_or_active(old_state)) {
            break;
        }
        migrate_set_state(&s->state, old_state, MIGRATION_STATUS_CANCELLING);
    } while (s->state != MIGRATION_STATUS_CANCELLING);

    /*
     * If we're unlucky the migration code might be stuck somewhere in a
     * send/write while the network has failed and is waiting to timeout;
     * if we've got shutdown(2) available then we can force it to quit.
     * The outgoing qemu file gets closed in migrate_fd_cleanup that is
     * called in a bh, so there is no race against this cancel.
     */
    if (s->state == MIGRATION_STATUS_CANCELLING && f) {
        qemu_file_shutdown(f);
    }
    if (s->state == MIGRATION_STATUS_CANCELLING && s->block_inactive) {
        Error *local_err = NULL;

        bdrv_invalidate_cache_all(&local_err);
        if (local_err) {
            error_report_err(local_err);
        } else {
            s->block_inactive = false;
        }
    }
    block_cleanup_parameters(s);
}

void add_migration_state_change_notifier(Notifier *notify)
{
    notifier_list_add(&migration_state_notifiers, notify);
}

void remove_migration_state_change_notifier(Notifier *notify)
{
    notifier_remove(notify);
}

bool migration_in_setup(MigrationState *s)
{
    return s->state == MIGRATION_STATUS_SETUP;
}

bool migration_has_finished(MigrationState *s)
{
    return s->state == MIGRATION_STATUS_COMPLETED;
}

bool migration_has_failed(MigrationState *s)
{
    return (s->state == MIGRATION_STATUS_CANCELLED ||
            s->state == MIGRATION_STATUS_FAILED);
}

bool migration_in_postcopy(void)
{
    MigrationState *s = migrate_get_current();

    return (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
}

bool migration_in_postcopy_after_devices(MigrationState *s)
{
    return migration_in_postcopy() && s->postcopy_after_devices;
}

bool migration_is_idle(void)
{
    MigrationState *s = migrate_get_current();

    switch (s->state) {
    case MIGRATION_STATUS_NONE:
    case MIGRATION_STATUS_CANCELLED:
    case MIGRATION_STATUS_COMPLETED:
    case MIGRATION_STATUS_FAILED:
        return true;
    case MIGRATION_STATUS_SETUP:
    case MIGRATION_STATUS_CANCELLING:
    case MIGRATION_STATUS_ACTIVE:
    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
    case MIGRATION_STATUS_COLO:
        return false;
    case MIGRATION_STATUS__MAX:
        g_assert_not_reached();
    }

    return false;
}

MigrationState *migrate_init(void)
{
    MigrationState *s = migrate_get_current();

    /*
     * Reinitialise all migration state, except
     * parameters/capabilities that the user set, and
     * locks.
     */
    s->bytes_xfer = 0;
    s->xfer_limit = 0;
    s->cleanup_bh = 0;
    s->to_dst_file = NULL;
    s->state = MIGRATION_STATUS_NONE;
    s->rp_state.from_dst_file = NULL;
    s->rp_state.error = false;
    s->mbps = 0.0;
    s->downtime = 0;
    s->expected_downtime = 0;
    s->setup_time = 0;
    s->start_postcopy = false;
    s->postcopy_after_devices = false;
    s->migration_thread_running = false;
    error_free(s->error);
    s->error = NULL;

    migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);

    s->total_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
    return s;
}

static GSList *migration_blockers;

int migrate_add_blocker(Error *reason, Error **errp)
{
    if (only_migratable) {
        error_propagate(errp, error_copy(reason));
        error_prepend(errp, "disallowing migration blocker "
                          "(--only_migratable) for: ");
        return -EACCES;
    }

    if (migration_is_idle()) {
        migration_blockers = g_slist_prepend(migration_blockers, reason);
        return 0;
    }

    error_propagate(errp, error_copy(reason));
    error_prepend(errp, "disallowing migration blocker (migration in "
                      "progress) for: ");
    return -EBUSY;
}

void migrate_del_blocker(Error *reason)
{
    migration_blockers = g_slist_remove(migration_blockers, reason);
}

void qmp_migrate_incoming(const char *uri, Error **errp)
{
    Error *local_err = NULL;
    static bool once = true;

    if (!deferred_incoming) {
        error_setg(errp, "For use with '-incoming defer'");
        return;
    }
    if (!once) {
        error_setg(errp, "The incoming migration has already been started");
    }

    qemu_start_incoming_migration(uri, &local_err);

    if (local_err) {
        error_propagate(errp, local_err);
        return;
    }

    once = false;
}

bool migration_is_blocked(Error **errp)
{
    if (qemu_savevm_state_blocked(errp)) {
        return true;
    }

    if (migration_blockers) {
        error_propagate(errp, error_copy(migration_blockers->data));
        return true;
    }

    return false;
}

void qmp_migrate(const char *uri, bool has_blk, bool blk,
                 bool has_inc, bool inc, bool has_detach, bool detach,
                 Error **errp)
{
    Error *local_err = NULL;
    MigrationState *s = migrate_get_current();
    const char *p;

    if (migration_is_setup_or_active(s->state) ||
        s->state == MIGRATION_STATUS_CANCELLING ||
        s->state == MIGRATION_STATUS_COLO) {
        error_setg(errp, QERR_MIGRATION_ACTIVE);
        return;
    }
    if (runstate_check(RUN_STATE_INMIGRATE)) {
        error_setg(errp, "Guest is waiting for an incoming migration");
        return;
    }

    if (migration_is_blocked(errp)) {
        return;
    }

    if ((has_blk && blk) || (has_inc && inc)) {
        if (migrate_use_block() || migrate_use_block_incremental()) {
            error_setg(errp, "Command options are incompatible with "
                       "current migration capabilities");
            return;
        }
        migrate_set_block_enabled(true, &local_err);
        if (local_err) {
            error_propagate(errp, local_err);
            return;
        }
        s->must_remove_block_options = true;
    }

    if (has_inc && inc) {
        migrate_set_block_incremental(s, true);
    }

    s = migrate_init();

    if (strstart(uri, "tcp:", &p)) {
        tcp_start_outgoing_migration(s, p, &local_err);
#ifdef CONFIG_RDMA
    } else if (strstart(uri, "rdma:", &p)) {
        rdma_start_outgoing_migration(s, p, &local_err);
#endif
    } else if (strstart(uri, "exec:", &p)) {
        exec_start_outgoing_migration(s, p, &local_err);
    } else if (strstart(uri, "unix:", &p)) {
        unix_start_outgoing_migration(s, p, &local_err);
    } else if (strstart(uri, "fd:", &p)) {
        fd_start_outgoing_migration(s, p, &local_err);
    } else {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "uri",
                   "a valid migration protocol");
        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                          MIGRATION_STATUS_FAILED);
        return;
    }

    if (local_err) {
        migrate_fd_error(s, local_err);
        error_propagate(errp, local_err);
        return;
    }
}

void qmp_migrate_cancel(Error **errp)
{
    migrate_fd_cancel(migrate_get_current());
}

void qmp_migrate_set_cache_size(int64_t value, Error **errp)
{
    MigrationState *s = migrate_get_current();
    int64_t new_size;

    /* Check for truncation */
    if (value != (size_t)value) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
                   "exceeding address space");
        return;
    }

    /* Cache should not be larger than guest ram size */
    if (value > ram_bytes_total()) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
                   "exceeds guest ram size ");
        return;
    }

    new_size = xbzrle_cache_resize(value);
    if (new_size < 0) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
                   "is smaller than page size");
        return;
    }

    s->xbzrle_cache_size = new_size;
}

int64_t qmp_query_migrate_cache_size(Error **errp)
{
    return migrate_xbzrle_cache_size();
}

void qmp_migrate_set_speed(int64_t value, Error **errp)
{
    MigrationParameters p = {
        .has_max_bandwidth = true,
        .max_bandwidth = value,
    };

    qmp_migrate_set_parameters(&p, errp);
}

void qmp_migrate_set_downtime(double value, Error **errp)
{
    if (value < 0 || value > MAX_MIGRATE_DOWNTIME_SECONDS) {
        error_setg(errp, "Parameter 'downtime_limit' expects an integer in "
                         "the range of 0 to %d seconds",
                         MAX_MIGRATE_DOWNTIME_SECONDS);
        return;
    }

    value *= 1000; /* Convert to milliseconds */
    value = MAX(0, MIN(INT64_MAX, value));

    MigrationParameters p = {
        .has_downtime_limit = true,
        .downtime_limit = value,
    };

    qmp_migrate_set_parameters(&p, errp);
}

bool migrate_release_ram(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_RELEASE_RAM];
}

bool migrate_postcopy_ram(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM];
}

bool migrate_auto_converge(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_AUTO_CONVERGE];
}

bool migrate_zero_blocks(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_ZERO_BLOCKS];
}

bool migrate_use_compression(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_COMPRESS];
}

int migrate_compress_level(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->parameters.compress_level;
}

int migrate_compress_threads(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->parameters.compress_threads;
}

int migrate_decompress_threads(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->parameters.decompress_threads;
}

bool migrate_use_events(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_EVENTS];
}

int migrate_use_xbzrle(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_XBZRLE];
}

int64_t migrate_xbzrle_cache_size(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->xbzrle_cache_size;
}

bool migrate_use_block(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->enabled_capabilities[MIGRATION_CAPABILITY_BLOCK];
}

bool migrate_use_block_incremental(void)
{
    MigrationState *s;

    s = migrate_get_current();

    return s->parameters.block_incremental;
}

/* migration thread support */
/*
 * Something bad happened to the RP stream, mark an error
 * The caller shall print or trace something to indicate why
 */
static void mark_source_rp_bad(MigrationState *s)
{
    s->rp_state.error = true;
}

static struct rp_cmd_args {
    ssize_t     len; /* -1 = variable */
    const char *name;
} rp_cmd_args[] = {
    [MIG_RP_MSG_INVALID]        = { .len = -1, .name = "INVALID" },
    [MIG_RP_MSG_SHUT]           = { .len =  4, .name = "SHUT" },
    [MIG_RP_MSG_PONG]           = { .len =  4, .name = "PONG" },
    [MIG_RP_MSG_REQ_PAGES]      = { .len = 12, .name = "REQ_PAGES" },
    [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
    [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
};

/*
 * Process a request for pages received on the return path,
 * We're allowed to send more than requested (e.g. to round to our page size)
 * and we don't need to send pages that have already been sent.
 */
static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
                                       ram_addr_t start, size_t len)
{
    long our_host_ps = getpagesize();

    trace_migrate_handle_rp_req_pages(rbname, start, len);

    /*
     * Since we currently insist on matching page sizes, just sanity check
     * we're being asked for whole host pages.
     */
    if (start & (our_host_ps-1) ||
       (len & (our_host_ps-1))) {
        error_report("%s: Misaligned page request, start: " RAM_ADDR_FMT
                     " len: %zd", __func__, start, len);
        mark_source_rp_bad(ms);
        return;
    }

    if (ram_save_queue_pages(rbname, start, len)) {
        mark_source_rp_bad(ms);
    }
}

/*
 * Handles messages sent on the return path towards the source VM
 *
 */
static void *source_return_path_thread(void *opaque)
{
    MigrationState *ms = opaque;
    QEMUFile *rp = ms->rp_state.from_dst_file;
    uint16_t header_len, header_type;
    uint8_t buf[512];
    uint32_t tmp32, sibling_error;
    ram_addr_t start = 0; /* =0 to silence warning */
    size_t  len = 0, expected_len;
    int res;

    trace_source_return_path_thread_entry();
    while (!ms->rp_state.error && !qemu_file_get_error(rp) &&
           migration_is_setup_or_active(ms->state)) {
        trace_source_return_path_thread_loop_top();
        header_type = qemu_get_be16(rp);
        header_len = qemu_get_be16(rp);

        if (header_type >= MIG_RP_MSG_MAX ||
            header_type == MIG_RP_MSG_INVALID) {
            error_report("RP: Received invalid message 0x%04x length 0x%04x",
                    header_type, header_len);
            mark_source_rp_bad(ms);
            goto out;
        }

        if ((rp_cmd_args[header_type].len != -1 &&
            header_len != rp_cmd_args[header_type].len) ||
            header_len > sizeof(buf)) {
            error_report("RP: Received '%s' message (0x%04x) with"
                    "incorrect length %d expecting %zu",
                    rp_cmd_args[header_type].name, header_type, header_len,
                    (size_t)rp_cmd_args[header_type].len);
            mark_source_rp_bad(ms);
            goto out;
        }

        /* We know we've got a valid header by this point */
        res = qemu_get_buffer(rp, buf, header_len);
        if (res != header_len) {
            error_report("RP: Failed reading data for message 0x%04x"
                         " read %d expected %d",
                         header_type, res, header_len);
            mark_source_rp_bad(ms);
            goto out;
        }

        /* OK, we have the message and the data */
        switch (header_type) {
        case MIG_RP_MSG_SHUT:
            sibling_error = ldl_be_p(buf);
            trace_source_return_path_thread_shut(sibling_error);
            if (sibling_error) {
                error_report("RP: Sibling indicated error %d", sibling_error);
                mark_source_rp_bad(ms);
            }
            /*
             * We'll let the main thread deal with closing the RP
             * we could do a shutdown(2) on it, but we're the only user
             * anyway, so there's nothing gained.
             */
            goto out;

        case MIG_RP_MSG_PONG:
            tmp32 = ldl_be_p(buf);
            trace_source_return_path_thread_pong(tmp32);
            break;

        case MIG_RP_MSG_REQ_PAGES:
            start = ldq_be_p(buf);
            len = ldl_be_p(buf + 8);
            migrate_handle_rp_req_pages(ms, NULL, start, len);
            break;

        case MIG_RP_MSG_REQ_PAGES_ID:
            expected_len = 12 + 1; /* header + termination */

            if (header_len >= expected_len) {
                start = ldq_be_p(buf);
                len = ldl_be_p(buf + 8);
                /* Now we expect an idstr */
                tmp32 = buf[12]; /* Length of the following idstr */
                buf[13 + tmp32] = '\0';
                expected_len += tmp32;
            }
            if (header_len != expected_len) {
                error_report("RP: Req_Page_id with length %d expecting %zd",
                        header_len, expected_len);
                mark_source_rp_bad(ms);
                goto out;
            }
            migrate_handle_rp_req_pages(ms, (char *)&buf[13], start, len);
            break;

        default:
            break;
        }
    }
    if (qemu_file_get_error(rp)) {
        trace_source_return_path_thread_bad_end();
        mark_source_rp_bad(ms);
    }

    trace_source_return_path_thread_end();
out:
    ms->rp_state.from_dst_file = NULL;
    qemu_fclose(rp);
    return NULL;
}

static int open_return_path_on_source(MigrationState *ms)
{

    ms->rp_state.from_dst_file = qemu_file_get_return_path(ms->to_dst_file);
    if (!ms->rp_state.from_dst_file) {
        return -1;
    }

    trace_open_return_path_on_source();
    qemu_thread_create(&ms->rp_state.rp_thread, "return path",
                       source_return_path_thread, ms, QEMU_THREAD_JOINABLE);

    trace_open_return_path_on_source_continue();

    return 0;
}

/* Returns 0 if the RP was ok, otherwise there was an error on the RP */
static int await_return_path_close_on_source(MigrationState *ms)
{
    /*
     * If this is a normal exit then the destination will send a SHUT and the
     * rp_thread will exit, however if there's an error we need to cause
     * it to exit.
     */
    if (qemu_file_get_error(ms->to_dst_file) && ms->rp_state.from_dst_file) {
        /*
         * shutdown(2), if we have it, will cause it to unblock if it's stuck
         * waiting for the destination.
         */
        qemu_file_shutdown(ms->rp_state.from_dst_file);
        mark_source_rp_bad(ms);
    }
    trace_await_return_path_close_on_source_joining();
    qemu_thread_join(&ms->rp_state.rp_thread);
    trace_await_return_path_close_on_source_close();
    return ms->rp_state.error;
}

/*
 * Switch from normal iteration to postcopy
 * Returns non-0 on error
 */
static int postcopy_start(MigrationState *ms, bool *old_vm_running)
{
    int ret;
    QIOChannelBuffer *bioc;
    QEMUFile *fb;
    int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
    bool restart_block = false;
    migrate_set_state(&ms->state, MIGRATION_STATUS_ACTIVE,
                      MIGRATION_STATUS_POSTCOPY_ACTIVE);

    trace_postcopy_start();
    qemu_mutex_lock_iothread();
    trace_postcopy_start_set_run();

    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
    *old_vm_running = runstate_is_running();
    global_state_store();
    ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
    if (ret < 0) {
        goto fail;
    }

    ret = bdrv_inactivate_all();
    if (ret < 0) {
        goto fail;
    }
    restart_block = true;

    /*
     * Cause any non-postcopiable, but iterative devices to
     * send out their final data.
     */
    qemu_savevm_state_complete_precopy(ms->to_dst_file, true);

    /*
     * in Finish migrate and with the io-lock held everything should
     * be quiet, but we've potentially still got dirty pages and we
     * need to tell the destination to throw any pages it's already received
     * that are dirty
     */
    if (ram_postcopy_send_discard_bitmap(ms)) {
        error_report("postcopy send discard bitmap failed");
        goto fail;
    }

    /*
     * send rest of state - note things that are doing postcopy
     * will notice we're in POSTCOPY_ACTIVE and not actually
     * wrap their state up here
     */
    qemu_file_set_rate_limit(ms->to_dst_file, INT64_MAX);
    /* Ping just for debugging, helps line traces up */
    qemu_savevm_send_ping(ms->to_dst_file, 2);

    /*
     * While loading the device state we may trigger page transfer
     * requests and the fd must be free to process those, and thus
     * the destination must read the whole device state off the fd before
     * it starts processing it.  Unfortunately the ad-hoc migration format
     * doesn't allow the destination to know the size to read without fully
     * parsing it through each devices load-state code (especially the open
     * coded devices that use get/put).
     * So we wrap the device state up in a package with a length at the start;
     * to do this we use a qemu_buf to hold the whole of the device state.
     */
    bioc = qio_channel_buffer_new(4096);
    qio_channel_set_name(QIO_CHANNEL(bioc), "migration-postcopy-buffer");
    fb = qemu_fopen_channel_output(QIO_CHANNEL(bioc));
    object_unref(OBJECT(bioc));

    /*
     * Make sure the receiver can get incoming pages before we send the rest
     * of the state
     */
    qemu_savevm_send_postcopy_listen(fb);

    qemu_savevm_state_complete_precopy(fb, false);
    qemu_savevm_send_ping(fb, 3);

    qemu_savevm_send_postcopy_run(fb);

    /* <><> end of stuff going into the package */

    /* Last point of recovery; as soon as we send the package the destination
     * can open devices and potentially start running.
     * Lets just check again we've not got any errors.
     */
    ret = qemu_file_get_error(ms->to_dst_file);
    if (ret) {
        error_report("postcopy_start: Migration stream errored (pre package)");
        goto fail_closefb;
    }

    restart_block = false;

    /* Now send that blob */
    if (qemu_savevm_send_packaged(ms->to_dst_file, bioc->data, bioc->usage)) {
        goto fail_closefb;
    }
    qemu_fclose(fb);

    /* Send a notify to give a chance for anything that needs to happen
     * at the transition to postcopy and after the device state; in particular
     * spice needs to trigger a transition now
     */
    ms->postcopy_after_devices = true;
    notifier_list_notify(&migration_state_notifiers, ms);

    ms->downtime =  qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - time_at_stop;

    qemu_mutex_unlock_iothread();

    /*
     * Although this ping is just for debug, it could potentially be
     * used for getting a better measurement of downtime at the source.
     */
    qemu_savevm_send_ping(ms->to_dst_file, 4);

    if (migrate_release_ram()) {
        ram_postcopy_migrated_memory_release(ms);
    }

    ret = qemu_file_get_error(ms->to_dst_file);
    if (ret) {
        error_report("postcopy_start: Migration stream errored");
        migrate_set_state(&ms->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
                              MIGRATION_STATUS_FAILED);
    }

    return ret;

fail_closefb:
    qemu_fclose(fb);
fail:
    migrate_set_state(&ms->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
                          MIGRATION_STATUS_FAILED);
    if (restart_block) {
        /* A failure happened early enough that we know the destination hasn't
         * accessed block devices, so we're safe to recover.
         */
        Error *local_err = NULL;

        bdrv_invalidate_cache_all(&local_err);
        if (local_err) {
            error_report_err(local_err);
        }
    }
    qemu_mutex_unlock_iothread();
    return -1;
}

/**
 * migration_completion: Used by migration_thread when there's not much left.
 *   The caller 'breaks' the loop when this returns.
 *
 * @s: Current migration state
 * @current_active_state: The migration state we expect to be in
 * @*old_vm_running: Pointer to old_vm_running flag
 * @*start_time: Pointer to time to update
 */
static void migration_completion(MigrationState *s, int current_active_state,
                                 bool *old_vm_running,
                                 int64_t *start_time)
{
    int ret;

    if (s->state == MIGRATION_STATUS_ACTIVE) {
        qemu_mutex_lock_iothread();
        *start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
        *old_vm_running = runstate_is_running();
        ret = global_state_store();

        if (!ret) {
            ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
            if (ret >= 0) {
                qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX);
                qemu_savevm_state_complete_precopy(s->to_dst_file, false);
            }
            /*
             * Don't mark the image with BDRV_O_INACTIVE flag if
             * we will go into COLO stage later.
             */
            if (ret >= 0 && !migrate_colo_enabled()) {
                ret = bdrv_inactivate_all();
                if (ret >= 0) {
                    s->block_inactive = true;
                }
            }
        }
        qemu_mutex_unlock_iothread();

        if (ret < 0) {
            goto fail;
        }
    } else if (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
        trace_migration_completion_postcopy_end();

        qemu_savevm_state_complete_postcopy(s->to_dst_file);
        trace_migration_completion_postcopy_end_after_complete();
    }

    /*
     * If rp was opened we must clean up the thread before
     * cleaning everything else up (since if there are no failures
     * it will wait for the destination to send it's status in
     * a SHUT command).
     */
    if (s->rp_state.from_dst_file) {
        int rp_error;
        trace_migration_return_path_end_before();
        rp_error = await_return_path_close_on_source(s);
        trace_migration_return_path_end_after(rp_error);
        if (rp_error) {
            goto fail_invalidate;
        }
    }

    if (qemu_file_get_error(s->to_dst_file)) {
        trace_migration_completion_file_err();
        goto fail_invalidate;
    }

    if (!migrate_colo_enabled()) {
        migrate_set_state(&s->state, current_active_state,
                          MIGRATION_STATUS_COMPLETED);
    }

    return;

fail_invalidate:
    /* If not doing postcopy, vm_start() will be called: let's regain
     * control on images.
     */
    if (s->state == MIGRATION_STATUS_ACTIVE) {
        Error *local_err = NULL;

        qemu_mutex_lock_iothread();
        bdrv_invalidate_cache_all(&local_err);
        if (local_err) {
            error_report_err(local_err);
        } else {
            s->block_inactive = false;
        }
        qemu_mutex_unlock_iothread();
    }

fail:
    migrate_set_state(&s->state, current_active_state,
                      MIGRATION_STATUS_FAILED);
}

bool migrate_colo_enabled(void)
{
    MigrationState *s = migrate_get_current();
    return s->enabled_capabilities[MIGRATION_CAPABILITY_X_COLO];
}

/*
 * Master migration thread on the source VM.
 * It drives the migration and pumps the data down the outgoing channel.
 */
static void *migration_thread(void *opaque)
{
    MigrationState *s = opaque;
    /* Used by the bandwidth calcs, updated later */
    int64_t initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
    int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
    int64_t initial_bytes = 0;
    /*
     * The final stage happens when the remaining data is smaller than
     * this threshold; it's calculated from the requested downtime and
     * measured bandwidth
     */
    int64_t threshold_size = 0;
    int64_t start_time = initial_time;
    int64_t end_time;
    bool old_vm_running = false;
    bool entered_postcopy = false;
    /* The active state we expect to be in; ACTIVE or POSTCOPY_ACTIVE */
    enum MigrationStatus current_active_state = MIGRATION_STATUS_ACTIVE;
    bool enable_colo = migrate_colo_enabled();

    rcu_register_thread();

    qemu_savevm_state_header(s->to_dst_file);

    if (s->to_dst_file) {
        /* Now tell the dest that it should open its end so it can reply */
        qemu_savevm_send_open_return_path(s->to_dst_file);

        /* And do a ping that will make stuff easier to debug */
        qemu_savevm_send_ping(s->to_dst_file, 1);
    }

    if (migrate_postcopy_ram()) {
        /*
         * Tell the destination that we *might* want to do postcopy later;
         * if the other end can't do postcopy it should fail now, nice and
         * early.
         */
        qemu_savevm_send_postcopy_advise(s->to_dst_file);
    }

    qemu_savevm_state_begin(s->to_dst_file);

    s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                      MIGRATION_STATUS_ACTIVE);

    trace_migration_thread_setup_complete();

    while (s->state == MIGRATION_STATUS_ACTIVE ||
           s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
        int64_t current_time;
        uint64_t pending_size;

        if (!qemu_file_rate_limit(s->to_dst_file)) {
            uint64_t pend_post, pend_nonpost;

            qemu_savevm_state_pending(s->to_dst_file, threshold_size,
                                      &pend_nonpost, &pend_post);
            pending_size = pend_nonpost + pend_post;
            trace_migrate_pending(pending_size, threshold_size,
                                  pend_post, pend_nonpost);
            if (pending_size && pending_size >= threshold_size) {
                /* Still a significant amount to transfer */

                if (migrate_postcopy_ram() &&
                    s->state != MIGRATION_STATUS_POSTCOPY_ACTIVE &&
                    pend_nonpost <= threshold_size &&
                    atomic_read(&s->start_postcopy)) {

                    if (!postcopy_start(s, &old_vm_running)) {
                        current_active_state = MIGRATION_STATUS_POSTCOPY_ACTIVE;
                        entered_postcopy = true;
                    }

                    continue;
                }
                /* Just another iteration step */
                qemu_savevm_state_iterate(s->to_dst_file, entered_postcopy);
            } else {
                trace_migration_thread_low_pending(pending_size);
                migration_completion(s, current_active_state,
                                     &old_vm_running, &start_time);
                break;
            }
        }

        if (qemu_file_get_error(s->to_dst_file)) {
            migrate_set_state(&s->state, current_active_state,
                              MIGRATION_STATUS_FAILED);
            trace_migration_thread_file_err();
            break;
        }
        current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
        if (current_time >= initial_time + BUFFER_DELAY) {
            uint64_t transferred_bytes = qemu_ftell(s->to_dst_file) -
                                         initial_bytes;
            uint64_t time_spent = current_time - initial_time;
            double bandwidth = (double)transferred_bytes / time_spent;
            threshold_size = bandwidth * s->parameters.downtime_limit;

            s->mbps = (((double) transferred_bytes * 8.0) /
                    ((double) time_spent / 1000.0)) / 1000.0 / 1000.0;

            trace_migrate_transferred(transferred_bytes, time_spent,
                                      bandwidth, threshold_size);
            /* if we haven't sent anything, we don't want to recalculate
               10000 is a small enough number for our purposes */
            if (ram_counters.dirty_pages_rate && transferred_bytes > 10000) {
                s->expected_downtime = ram_counters.dirty_pages_rate *
                    qemu_target_page_size() / bandwidth;
            }

            qemu_file_reset_rate_limit(s->to_dst_file);
            initial_time = current_time;
            initial_bytes = qemu_ftell(s->to_dst_file);
        }
        if (qemu_file_rate_limit(s->to_dst_file)) {
            /* usleep expects microseconds */
            g_usleep((initial_time + BUFFER_DELAY - current_time)*1000);
        }
    }

    trace_migration_thread_after_loop();
    /* If we enabled cpu throttling for auto-converge, turn it off. */
    cpu_throttle_stop();
    end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

    qemu_mutex_lock_iothread();
    /*
     * The resource has been allocated by migration will be reused in COLO
     * process, so don't release them.
     */
    if (!enable_colo) {
        qemu_savevm_state_cleanup();
    }
    if (s->state == MIGRATION_STATUS_COMPLETED) {
        uint64_t transferred_bytes = qemu_ftell(s->to_dst_file);
        s->total_time = end_time - s->total_time;
        if (!entered_postcopy) {
            s->downtime = end_time - start_time;
        }
        if (s->total_time) {
            s->mbps = (((double) transferred_bytes * 8.0) /
                       ((double) s->total_time)) / 1000;
        }
        runstate_set(RUN_STATE_POSTMIGRATE);
    } else {
        if (s->state == MIGRATION_STATUS_ACTIVE && enable_colo) {
            migrate_start_colo_process(s);
            qemu_savevm_state_cleanup();
            /*
            * Fixme: we will run VM in COLO no matter its old running state.
            * After exited COLO, we will keep running.
            */
            old_vm_running = true;
        }
        if (old_vm_running && !entered_postcopy) {
            vm_start();
        } else {
            if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
                runstate_set(RUN_STATE_POSTMIGRATE);
            }
        }
    }
    qemu_bh_schedule(s->cleanup_bh);
    qemu_mutex_unlock_iothread();

    rcu_unregister_thread();
    return NULL;
}

void migrate_fd_connect(MigrationState *s)
{
    s->expected_downtime = s->parameters.downtime_limit;
    s->cleanup_bh = qemu_bh_new(migrate_fd_cleanup, s);

    qemu_file_set_blocking(s->to_dst_file, true);
    qemu_file_set_rate_limit(s->to_dst_file,
                             s->parameters.max_bandwidth / XFER_LIMIT_RATIO);

    /* Notify before starting migration thread */
    notifier_list_notify(&migration_state_notifiers, s);

    /*
     * Open the return path; currently for postcopy but other things might
     * also want it.
     */
    if (migrate_postcopy_ram()) {
        if (open_return_path_on_source(s)) {
            error_report("Unable to open return-path for postcopy");
            migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                              MIGRATION_STATUS_FAILED);
            migrate_fd_cleanup(s);
            return;
        }
    }

    migrate_compress_threads_create();
    qemu_thread_create(&s->thread, "live_migration", migration_thread, s,
                       QEMU_THREAD_JOINABLE);
    s->migration_thread_running = true;
}