Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 4358 insertions, 0 deletions

diff --git a/migration/migration.c b/migration/migration.c
new file mode 100644
index 000000000..abaf6f9e3
--- /dev/null
+++ b/migration/migration.c
@@ -0,0 +1,4358 @@
+/*
+ * 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 "sysemu/runstate.h"
+#include "sysemu/sysemu.h"
+#include "sysemu/cpu-throttle.h"
+#include "rdma.h"
+#include "ram.h"
+#include "migration/global_state.h"
+#include "migration/misc.h"
+#include "migration.h"
+#include "savevm.h"
+#include "qemu-file-channel.h"
+#include "qemu-file.h"
+#include "migration/vmstate.h"
+#include "block/block.h"
+#include "qapi/error.h"
+#include "qapi/clone-visitor.h"
+#include "qapi/qapi-visit-migration.h"
+#include "qapi/qapi-visit-sockets.h"
+#include "qapi/qapi-commands-migration.h"
+#include "qapi/qapi-events-migration.h"
+#include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qnull.h"
+#include "qemu/rcu.h"
+#include "block.h"
+#include "postcopy-ram.h"
+#include "qemu/thread.h"
+#include "trace.h"
+#include "exec/target_page.h"
+#include "io/channel-buffer.h"
+#include "migration/colo.h"
+#include "hw/boards.h"
+#include "hw/qdev-properties.h"
+#include "hw/qdev-properties-system.h"
+#include "monitor/monitor.h"
+#include "net/announce.h"
+#include "qemu/queue.h"
+#include "multifd.h"
+#include "qemu/yank.h"
+#include "sysemu/cpus.h"
+#include "yank_functions.h"
+
+#define MAX_THROTTLE  (128 << 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_THROTTLE_TRIGGER_THRESHOLD 50
+#define DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL 20
+#define DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT 10
+#define DEFAULT_MIGRATE_MAX_CPU_THROTTLE 99
+
+/* Migration XBZRLE default cache size */
+#define DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE (64 * 1024 * 1024)
+
+/* The delay time (in ms) between two COLO checkpoints */
+#define DEFAULT_MIGRATE_X_CHECKPOINT_DELAY (200 * 100)
+#define DEFAULT_MIGRATE_MULTIFD_CHANNELS 2
+#define DEFAULT_MIGRATE_MULTIFD_COMPRESSION MULTIFD_COMPRESSION_NONE
+/* 0: means nocompress, 1: best speed, ... 9: best compress ratio */
+#define DEFAULT_MIGRATE_MULTIFD_ZLIB_LEVEL 1
+/* 0: means nocompress, 1: best speed, ... 20: best compress ratio */
+#define DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL 1
+
+/* Background transfer rate for postcopy, 0 means unlimited, note
+ * that page requests can still exceed this limit.
+ */
+#define DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH 0
+
+/*
+ * Parameters for self_announce_delay giving a stream of RARP/ARP
+ * packets after migration.
+ */
+#define DEFAULT_MIGRATE_ANNOUNCE_INITIAL  50
+#define DEFAULT_MIGRATE_ANNOUNCE_MAX     550
+#define DEFAULT_MIGRATE_ANNOUNCE_ROUNDS    5
+#define DEFAULT_MIGRATE_ANNOUNCE_STEP    100
+
+static NotifierList migration_state_notifiers =
+    NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
+
+/* Messages sent on the return path from destination to source */
+enum mig_rp_message_type {
+    MIG_RP_MSG_INVALID = 0,  /* Must be 0 */
+    MIG_RP_MSG_SHUT,         /* sibling will not send any more RP messages */
+    MIG_RP_MSG_PONG,         /* Response to a PING; data (seq: be32 ) */
+
+    MIG_RP_MSG_REQ_PAGES_ID, /* data (start: be64, len: be32, id: string) */
+    MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
+    MIG_RP_MSG_RECV_BITMAP,  /* send recved_bitmap back to source */
+    MIG_RP_MSG_RESUME_ACK,   /* tell source that we are ready to resume */
+
+    MIG_RP_MSG_MAX
+};
+
+/* Migration capabilities set */
+struct MigrateCapsSet {
+    int size;                       /* Capability set size */
+    MigrationCapability caps[];     /* Variadic array of capabilities */
+};
+typedef struct MigrateCapsSet MigrateCapsSet;
+
+/* Define and initialize MigrateCapsSet */
+#define INITIALIZE_MIGRATE_CAPS_SET(_name, ...)   \
+    MigrateCapsSet _name = {    \
+        .size = sizeof((int []) { __VA_ARGS__ }) / sizeof(int), \
+        .caps = { __VA_ARGS__ } \
+    }
+
+/* Background-snapshot compatibility check list */
+static const
+INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snapshot,
+    MIGRATION_CAPABILITY_POSTCOPY_RAM,
+    MIGRATION_CAPABILITY_DIRTY_BITMAPS,
+    MIGRATION_CAPABILITY_POSTCOPY_BLOCKTIME,
+    MIGRATION_CAPABILITY_LATE_BLOCK_ACTIVATE,
+    MIGRATION_CAPABILITY_RETURN_PATH,
+    MIGRATION_CAPABILITY_MULTIFD,
+    MIGRATION_CAPABILITY_PAUSE_BEFORE_SWITCHOVER,
+    MIGRATION_CAPABILITY_AUTO_CONVERGE,
+    MIGRATION_CAPABILITY_RELEASE_RAM,
+    MIGRATION_CAPABILITY_RDMA_PIN_ALL,
+    MIGRATION_CAPABILITY_COMPRESS,
+    MIGRATION_CAPABILITY_XBZRLE,
+    MIGRATION_CAPABILITY_X_COLO,
+    MIGRATION_CAPABILITY_VALIDATE_UUID);
+
+/* When we add fault tolerance, we could have several
+   migrations at once.  For now we don't need to add
+   dynamic creation of migration */
+
+static MigrationState *current_migration;
+static MigrationIncomingState *current_incoming;
+
+static GSList *migration_blockers;
+
+static bool migration_object_check(MigrationState *ms, Error **errp);
+static int migration_maybe_pause(MigrationState *s,
+                                 int *current_active_state,
+                                 int new_state);
+static void migrate_fd_cancel(MigrationState *s);
+
+static gint page_request_addr_cmp(gconstpointer ap, gconstpointer bp)
+{
+    uintptr_t a = (uintptr_t) ap, b = (uintptr_t) bp;
+
+    return (a > b) - (a < b);
+}
+
+void migration_object_init(void)
+{
+    /* This can only be called once. */
+    assert(!current_migration);
+    current_migration = MIGRATION_OBJ(object_new(TYPE_MIGRATION));
+
+    /*
+     * Init the migrate incoming object as well no matter whether
+     * we'll use it or not.
+     */
+    assert(!current_incoming);
+    current_incoming = g_new0(MigrationIncomingState, 1);
+    current_incoming->state = MIGRATION_STATUS_NONE;
+    current_incoming->postcopy_remote_fds =
+        g_array_new(FALSE, TRUE, sizeof(struct PostCopyFD));
+    qemu_mutex_init(&current_incoming->rp_mutex);
+    qemu_event_init(&current_incoming->main_thread_load_event, false);
+    qemu_sem_init(&current_incoming->postcopy_pause_sem_dst, 0);
+    qemu_sem_init(&current_incoming->postcopy_pause_sem_fault, 0);
+    qemu_mutex_init(&current_incoming->page_request_mutex);
+    current_incoming->page_requested = g_tree_new(page_request_addr_cmp);
+
+    migration_object_check(current_migration, &error_fatal);
+
+    blk_mig_init();
+    ram_mig_init();
+    dirty_bitmap_mig_init();
+}
+
+void migration_cancel(const Error *error)
+{
+    if (error) {
+        migrate_set_error(current_migration, error);
+    }
+    migrate_fd_cancel(current_migration);
+}
+
+void migration_shutdown(void)
+{
+    /*
+     * Cancel the current migration - that will (eventually)
+     * stop the migration using this structure
+     */
+    migration_cancel(NULL);
+    object_unref(OBJECT(current_migration));
+
+    /*
+     * Cancel outgoing migration of dirty bitmaps. It should
+     * at least unref used block nodes.
+     */
+    dirty_bitmap_mig_cancel_outgoing();
+
+    /*
+     * Cancel incoming migration of dirty bitmaps. Dirty bitmaps
+     * are non-critical data, and their loss never considered as
+     * something serious.
+     */
+    dirty_bitmap_mig_cancel_incoming();
+}
+
+/* For outgoing */
+MigrationState *migrate_get_current(void)
+{
+    /* This can only be called after the object created. */
+    assert(current_migration);
+    return current_migration;
+}
+
+MigrationIncomingState *migration_incoming_get_current(void)
+{
+    assert(current_incoming);
+    return current_incoming;
+}
+
+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) {
+        migration_ioc_unregister_yank_from_file(mis->from_src_file);
+        qemu_fclose(mis->from_src_file);
+        mis->from_src_file = NULL;
+    }
+    if (mis->postcopy_remote_fds) {
+        g_array_free(mis->postcopy_remote_fds, TRUE);
+        mis->postcopy_remote_fds = NULL;
+    }
+    if (mis->transport_cleanup) {
+        mis->transport_cleanup(mis->transport_data);
+    }
+
+    qemu_event_reset(&mis->main_thread_load_event);
+
+    if (mis->page_requested) {
+        g_tree_destroy(mis->page_requested);
+        mis->page_requested = NULL;
+    }
+
+    if (mis->socket_address_list) {
+        qapi_free_SocketAddressList(mis->socket_address_list);
+        mis->socket_address_list = NULL;
+    }
+
+    yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+}
+
+static void migrate_generate_event(int new_state)
+{
+    if (migrate_use_events()) {
+        qapi_event_send_migration(new_state);
+    }
+}
+
+static bool migrate_late_block_activate(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[
+        MIGRATION_CAPABILITY_LATE_BLOCK_ACTIVATE];
+}
+
+/*
+ * Send a message on the return channel back to the source
+ * of the migration.
+ */
+static int migrate_send_rp_message(MigrationIncomingState *mis,
+                                   enum mig_rp_message_type message_type,
+                                   uint16_t len, void *data)
+{
+    int ret = 0;
+
+    trace_migrate_send_rp_message((int)message_type, len);
+    QEMU_LOCK_GUARD(&mis->rp_mutex);
+
+    /*
+     * It's possible that the file handle got lost due to network
+     * failures.
+     */
+    if (!mis->to_src_file) {
+        ret = -EIO;
+        return ret;
+    }
+
+    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);
+
+    /* It's possible that qemu file got error during sending */
+    ret = qemu_file_get_error(mis->to_src_file);
+
+    return ret;
+}
+
+/* Request one page from the source VM at the given start address.
+ *   rb: the RAMBlock to request the page in
+ *   Start: Address offset within the RB
+ *   Len: Length in bytes required - must be a multiple of pagesize
+ */
+int migrate_send_rp_message_req_pages(MigrationIncomingState *mis,
+                                      RAMBlock *rb, ram_addr_t start)
+{
+    uint8_t bufc[12 + 1 + 255]; /* start (8), len (4), rbname up to 256 */
+    size_t msglen = 12; /* start + len */
+    size_t len = qemu_ram_pagesize(rb);
+    enum mig_rp_message_type msg_type;
+    const char *rbname;
+    int rbname_len;
+
+    *(uint64_t *)bufc = cpu_to_be64((uint64_t)start);
+    *(uint32_t *)(bufc + 8) = cpu_to_be32((uint32_t)len);
+
+    /*
+     * We maintain the last ramblock that we requested for page.  Note that we
+     * don't need locking because this function will only be called within the
+     * postcopy ram fault thread.
+     */
+    if (rb != mis->last_rb) {
+        mis->last_rb = rb;
+
+        rbname = qemu_ram_get_idstr(rb);
+        rbname_len = strlen(rbname);
+
+        assert(rbname_len < 256);
+
+        bufc[msglen++] = rbname_len;
+        memcpy(bufc + msglen, rbname, rbname_len);
+        msglen += rbname_len;
+        msg_type = MIG_RP_MSG_REQ_PAGES_ID;
+    } else {
+        msg_type = MIG_RP_MSG_REQ_PAGES;
+    }
+
+    return migrate_send_rp_message(mis, msg_type, msglen, bufc);
+}
+
+int migrate_send_rp_req_pages(MigrationIncomingState *mis,
+                              RAMBlock *rb, ram_addr_t start, uint64_t haddr)
+{
+    void *aligned = (void *)(uintptr_t)ROUND_DOWN(haddr, qemu_ram_pagesize(rb));
+    bool received = false;
+
+    WITH_QEMU_LOCK_GUARD(&mis->page_request_mutex) {
+        received = ramblock_recv_bitmap_test_byte_offset(rb, start);
+        if (!received && !g_tree_lookup(mis->page_requested, aligned)) {
+            /*
+             * The page has not been received, and it's not yet in the page
+             * request list.  Queue it.  Set the value of element to 1, so that
+             * things like g_tree_lookup() will return TRUE (1) when found.
+             */
+            g_tree_insert(mis->page_requested, aligned, (gpointer)1);
+            mis->page_requested_count++;
+            trace_postcopy_page_req_add(aligned, mis->page_requested_count);
+        }
+    }
+
+    /*
+     * If the page is there, skip sending the message.  We don't even need the
+     * lock because as long as the page arrived, it'll be there forever.
+     */
+    if (received) {
+        return 0;
+    }
+
+    return migrate_send_rp_message_req_pages(mis, rb, start);
+}
+
+static bool migration_colo_enabled;
+bool migration_incoming_colo_enabled(void)
+{
+    return migration_colo_enabled;
+}
+
+void migration_incoming_disable_colo(void)
+{
+    ram_block_discard_disable(false);
+    migration_colo_enabled = false;
+}
+
+int migration_incoming_enable_colo(void)
+{
+    if (ram_block_discard_disable(true)) {
+        error_report("COLO: cannot disable RAM discard");
+        return -EBUSY;
+    }
+    migration_colo_enabled = true;
+    return 0;
+}
+
+void migrate_add_address(SocketAddress *address)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    QAPI_LIST_PREPEND(mis->socket_address_list,
+                      QAPI_CLONE(SocketAddress, address));
+}
+
+static void qemu_start_incoming_migration(const char *uri, Error **errp)
+{
+    const char *p = NULL;
+
+    migrate_protocol_allow_multifd(false); /* reset it anyway */
+    qapi_event_send_migration(MIGRATION_STATUS_SETUP);
+    if (strstart(uri, "tcp:", &p) ||
+        strstart(uri, "unix:", NULL) ||
+        strstart(uri, "vsock:", NULL)) {
+        migrate_protocol_allow_multifd(true);
+        socket_start_incoming_migration(p ? p : uri, 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, "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;
+
+    /* If capability late_block_activate is set:
+     * Only fire up the block code now if we're going to restart the
+     * VM, else 'cont' will do it.
+     * This causes file locking to happen; so we don't want it to happen
+     * unless we really are starting the VM.
+     */
+    if (!migrate_late_block_activate() ||
+         (autostart && (!global_state_received() ||
+            global_state_get_runstate() == RUN_STATE_RUNNING))) {
+        /* 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(&mis->announce_timer, migrate_announce_params());
+
+    if (multifd_load_cleanup(&local_err) != 0) {
+        error_report_err(local_err);
+        autostart = false;
+    }
+    /* 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. */
+
+    dirty_bitmap_mig_before_vm_start();
+
+    if (!global_state_received() ||
+        global_state_get_runstate() == RUN_STATE_RUNNING) {
+        if (autostart) {
+            vm_start();
+        } else {
+            runstate_set(RUN_STATE_PAUSED);
+        }
+    } else if (migration_incoming_colo_enabled()) {
+        migration_incoming_disable_colo();
+        vm_start();
+    } else {
+        runstate_set(global_state_get_runstate());
+    }
+    /*
+     * 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)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+    PostcopyState ps;
+    int ret;
+    Error *local_err = NULL;
+
+    assert(mis->from_src_file);
+    mis->migration_incoming_co = qemu_coroutine_self();
+    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(mis->from_src_file);
+
+    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_colo_enabled()) {
+        /* Make sure all file formats flush their mutable metadata */
+        bdrv_invalidate_cache_all(&local_err);
+        if (local_err) {
+            error_report_err(local_err);
+            goto fail;
+        }
+
+        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();
+
+        qemu_mutex_unlock_iothread();
+        /* Wait checkpoint incoming thread exit before free resource */
+        qemu_thread_join(&mis->colo_incoming_thread);
+        qemu_mutex_lock_iothread();
+        /* We hold the global iothread lock, so it is safe here */
+        colo_release_ram_cache();
+    }
+
+    if (ret < 0) {
+        error_report("load of migration failed: %s", strerror(-ret));
+        goto fail;
+    }
+    mis->bh = qemu_bh_new(process_incoming_migration_bh, mis);
+    qemu_bh_schedule(mis->bh);
+    mis->migration_incoming_co = NULL;
+    return;
+fail:
+    local_err = NULL;
+    migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
+                      MIGRATION_STATUS_FAILED);
+    qemu_fclose(mis->from_src_file);
+    if (multifd_load_cleanup(&local_err) != 0) {
+        error_report_err(local_err);
+    }
+    exit(EXIT_FAILURE);
+}
+
+/**
+ * migration_incoming_setup: Setup incoming migration
+ * @f: file for main migration channel
+ * @errp: where to put errors
+ *
+ * Returns: %true on success, %false on error.
+ */
+static bool migration_incoming_setup(QEMUFile *f, Error **errp)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (multifd_load_setup(errp) != 0) {
+        return false;
+    }
+
+    if (!mis->from_src_file) {
+        mis->from_src_file = f;
+    }
+    qemu_file_set_blocking(f, false);
+    return true;
+}
+
+void migration_incoming_process(void)
+{
+    Coroutine *co = qemu_coroutine_create(process_incoming_migration_co, NULL);
+    qemu_coroutine_enter(co);
+}
+
+/* Returns true if recovered from a paused migration, otherwise false */
+static bool postcopy_try_recover(QEMUFile *f)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (mis->state == MIGRATION_STATUS_POSTCOPY_PAUSED) {
+        /* Resumed from a paused postcopy migration */
+
+        mis->from_src_file = f;
+        /* Postcopy has standalone thread to do vm load */
+        qemu_file_set_blocking(f, true);
+
+        /* Re-configure the return path */
+        mis->to_src_file = qemu_file_get_return_path(f);
+
+        migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_PAUSED,
+                          MIGRATION_STATUS_POSTCOPY_RECOVER);
+
+        /*
+         * Here, we only wake up the main loading thread (while the
+         * fault thread will still be waiting), so that we can receive
+         * commands from source now, and answer it if needed. The
+         * fault thread will be woken up afterwards until we are sure
+         * that source is ready to reply to page requests.
+         */
+        qemu_sem_post(&mis->postcopy_pause_sem_dst);
+        return true;
+    }
+
+    return false;
+}
+
+void migration_fd_process_incoming(QEMUFile *f, Error **errp)
+{
+    if (postcopy_try_recover(f)) {
+        return;
+    }
+
+    if (!migration_incoming_setup(f, errp)) {
+        return;
+    }
+    migration_incoming_process();
+}
+
+void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+    Error *local_err = NULL;
+    bool start_migration;
+
+    if (!mis->from_src_file) {
+        /* The first connection (multifd may have multiple) */
+        QEMUFile *f = qemu_fopen_channel_input(ioc);
+
+        /* If it's a recovery, we're done */
+        if (postcopy_try_recover(f)) {
+            return;
+        }
+
+        if (!migration_incoming_setup(f, errp)) {
+            return;
+        }
+
+        /*
+         * Common migration only needs one channel, so we can start
+         * right now.  Multifd needs more than one channel, we wait.
+         */
+        start_migration = !migrate_use_multifd();
+    } else {
+        /* Multiple connections */
+        assert(migrate_use_multifd());
+        start_migration = multifd_recv_new_channel(ioc, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
+    if (start_migration) {
+        migration_incoming_process();
+    }
+}
+
+/**
+ * @migration_has_all_channels: We have received all channels that we need
+ *
+ * Returns true when we have got connections to all the channels that
+ * we need for migration.
+ */
+bool migration_has_all_channels(void)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+    bool all_channels;
+
+    all_channels = multifd_recv_all_channels_created();
+
+    return all_channels && mis->from_src_file != NULL;
+}
+
+/*
+ * 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);
+}
+
+void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
+                                 char *block_name)
+{
+    char buf[512];
+    int len;
+    int64_t res;
+
+    /*
+     * First, we send the header part. It contains only the len of
+     * idstr, and the idstr itself.
+     */
+    len = strlen(block_name);
+    buf[0] = len;
+    memcpy(buf + 1, block_name, len);
+
+    if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
+        error_report("%s: MSG_RP_RECV_BITMAP only used for recovery",
+                     __func__);
+        return;
+    }
+
+    migrate_send_rp_message(mis, MIG_RP_MSG_RECV_BITMAP, len + 1, buf);
+
+    /*
+     * Next, we dump the received bitmap to the stream.
+     *
+     * TODO: currently we are safe since we are the only one that is
+     * using the to_src_file handle (fault thread is still paused),
+     * and it's ok even not taking the mutex. However the best way is
+     * to take the lock before sending the message header, and release
+     * the lock after sending the bitmap.
+     */
+    qemu_mutex_lock(&mis->rp_mutex);
+    res = ramblock_recv_bitmap_send(mis->to_src_file, block_name);
+    qemu_mutex_unlock(&mis->rp_mutex);
+
+    trace_migrate_send_rp_recv_bitmap(block_name, res);
+}
+
+void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value)
+{
+    uint32_t buf;
+
+    buf = cpu_to_be32(value);
+    migrate_send_rp_message(mis, MIG_RP_MSG_RESUME_ACK, sizeof(buf), &buf);
+}
+
+MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
+{
+    MigrationCapabilityStatusList *head = NULL, **tail = &head;
+    MigrationCapabilityStatus *caps;
+    MigrationState *s = migrate_get_current();
+    int i;
+
+    for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
+#ifndef CONFIG_LIVE_BLOCK_MIGRATION
+        if (i == MIGRATION_CAPABILITY_BLOCK) {
+            continue;
+        }
+#endif
+        caps = g_malloc0(sizeof(*caps));
+        caps->capability = i;
+        caps->state = s->enabled_capabilities[i];
+        QAPI_LIST_APPEND(tail, caps);
+    }
+
+    return head;
+}
+
+MigrationParameters *qmp_query_migrate_parameters(Error **errp)
+{
+    MigrationParameters *params;
+    MigrationState *s = migrate_get_current();
+
+    /* TODO use QAPI_CLONE() instead of duplicating it inline */
+    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_compress_wait_thread = true;
+    params->compress_wait_thread = s->parameters.compress_wait_thread;
+    params->has_decompress_threads = true;
+    params->decompress_threads = s->parameters.decompress_threads;
+    params->has_throttle_trigger_threshold = true;
+    params->throttle_trigger_threshold = s->parameters.throttle_trigger_threshold;
+    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_cpu_throttle_tailslow = true;
+    params->cpu_throttle_tailslow = s->parameters.cpu_throttle_tailslow;
+    params->has_tls_creds = true;
+    params->tls_creds = g_strdup(s->parameters.tls_creds);
+    params->has_tls_hostname = true;
+    params->tls_hostname = g_strdup(s->parameters.tls_hostname);
+    params->has_tls_authz = true;
+    params->tls_authz = g_strdup(s->parameters.tls_authz ?
+                                 s->parameters.tls_authz : "");
+    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;
+    params->has_multifd_channels = true;
+    params->multifd_channels = s->parameters.multifd_channels;
+    params->has_multifd_compression = true;
+    params->multifd_compression = s->parameters.multifd_compression;
+    params->has_multifd_zlib_level = true;
+    params->multifd_zlib_level = s->parameters.multifd_zlib_level;
+    params->has_multifd_zstd_level = true;
+    params->multifd_zstd_level = s->parameters.multifd_zstd_level;
+    params->has_xbzrle_cache_size = true;
+    params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
+    params->has_max_postcopy_bandwidth = true;
+    params->max_postcopy_bandwidth = s->parameters.max_postcopy_bandwidth;
+    params->has_max_cpu_throttle = true;
+    params->max_cpu_throttle = s->parameters.max_cpu_throttle;
+    params->has_announce_initial = true;
+    params->announce_initial = s->parameters.announce_initial;
+    params->has_announce_max = true;
+    params->announce_max = s->parameters.announce_max;
+    params->has_announce_rounds = true;
+    params->announce_rounds = s->parameters.announce_rounds;
+    params->has_announce_step = true;
+    params->announce_step = s->parameters.announce_step;
+
+    if (s->parameters.has_block_bitmap_mapping) {
+        params->has_block_bitmap_mapping = true;
+        params->block_bitmap_mapping =
+            QAPI_CLONE(BitmapMigrationNodeAliasList,
+                       s->parameters.block_bitmap_mapping);
+    }
+
+    return params;
+}
+
+AnnounceParameters *migrate_announce_params(void)
+{
+    static AnnounceParameters ap;
+
+    MigrationState *s = migrate_get_current();
+
+    ap.initial = s->parameters.announce_initial;
+    ap.max = s->parameters.announce_max;
+    ap.rounds = s->parameters.announce_rounds;
+    ap.step = s->parameters.announce_step;
+
+    return &ap;
+}
+
+/*
+ * Return true if we're already in the middle of a migration
+ * (i.e. any of the active or setup states)
+ */
+bool migration_is_setup_or_active(int state)
+{
+    switch (state) {
+    case MIGRATION_STATUS_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_PAUSED:
+    case MIGRATION_STATUS_POSTCOPY_RECOVER:
+    case MIGRATION_STATUS_SETUP:
+    case MIGRATION_STATUS_PRE_SWITCHOVER:
+    case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_WAIT_UNPLUG:
+    case MIGRATION_STATUS_COLO:
+        return true;
+
+    default:
+        return false;
+
+    }
+}
+
+bool migration_is_running(int state)
+{
+    switch (state) {
+    case MIGRATION_STATUS_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_PAUSED:
+    case MIGRATION_STATUS_POSTCOPY_RECOVER:
+    case MIGRATION_STATUS_SETUP:
+    case MIGRATION_STATUS_PRE_SWITCHOVER:
+    case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_WAIT_UNPLUG:
+    case MIGRATION_STATUS_CANCELLING:
+        return true;
+
+    default:
+        return false;
+
+    }
+}
+
+static void populate_time_info(MigrationInfo *info, MigrationState *s)
+{
+    info->has_status = true;
+    info->has_setup_time = true;
+    info->setup_time = s->setup_time;
+    if (s->state == MIGRATION_STATUS_COMPLETED) {
+        info->has_total_time = true;
+        info->total_time = s->total_time;
+        info->has_downtime = true;
+        info->downtime = s->downtime;
+    } else {
+        info->has_total_time = true;
+        info->total_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) -
+                           s->start_time;
+        info->has_expected_downtime = true;
+        info->expected_downtime = s->expected_downtime;
+    }
+}
+
+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();
+    info->ram->multifd_bytes = ram_counters.multifd_bytes;
+    info->ram->pages_per_second = s->pages_per_second;
+
+    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->encoding_rate = xbzrle_counters.encoding_rate;
+        info->xbzrle_cache->overflow = xbzrle_counters.overflow;
+    }
+
+    if (migrate_use_compression()) {
+        info->has_compression = true;
+        info->compression = g_malloc0(sizeof(*info->compression));
+        info->compression->pages = compression_counters.pages;
+        info->compression->busy = compression_counters.busy;
+        info->compression->busy_rate = compression_counters.busy_rate;
+        info->compression->compressed_size =
+                                    compression_counters.compressed_size;
+        info->compression->compression_rate =
+                                    compression_counters.compression_rate;
+    }
+
+    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();
+    }
+}
+
+static void fill_source_migration_info(MigrationInfo *info)
+{
+    MigrationState *s = migrate_get_current();
+    GSList *cur_blocker = migration_blockers;
+
+    info->blocked_reasons = NULL;
+
+    /*
+     * There are two types of reasons a migration might be blocked;
+     * a) devices marked in VMState as non-migratable, and
+     * b) Explicit migration blockers
+     * We need to add both of them here.
+     */
+    qemu_savevm_non_migratable_list(&info->blocked_reasons);
+
+    while (cur_blocker) {
+        QAPI_LIST_PREPEND(info->blocked_reasons,
+                          g_strdup(error_get_pretty(cur_blocker->data)));
+        cur_blocker = g_slist_next(cur_blocker);
+    }
+    info->has_blocked_reasons = info->blocked_reasons != NULL;
+
+    switch (s->state) {
+    case MIGRATION_STATUS_NONE:
+        /* no migration has happened ever */
+        /* do not overwrite destination migration status */
+        return;
+    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:
+    case MIGRATION_STATUS_PRE_SWITCHOVER:
+    case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_POSTCOPY_PAUSED:
+    case MIGRATION_STATUS_POSTCOPY_RECOVER:
+        /* TODO add some postcopy stats */
+        populate_time_info(info, s);
+        populate_ram_info(info, s);
+        populate_disk_info(info);
+        populate_vfio_info(info);
+        break;
+    case MIGRATION_STATUS_COLO:
+        info->has_status = true;
+        /* TODO: display COLO specific information (checkpoint info etc.) */
+        break;
+    case MIGRATION_STATUS_COMPLETED:
+        populate_time_info(info, s);
+        populate_ram_info(info, s);
+        populate_vfio_info(info);
+        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;
+    case MIGRATION_STATUS_WAIT_UNPLUG:
+        info->has_status = true;
+        break;
+    }
+    info->status = s->state;
+}
+
+typedef enum WriteTrackingSupport {
+    WT_SUPPORT_UNKNOWN = 0,
+    WT_SUPPORT_ABSENT,
+    WT_SUPPORT_AVAILABLE,
+    WT_SUPPORT_COMPATIBLE
+} WriteTrackingSupport;
+
+static
+WriteTrackingSupport migrate_query_write_tracking(void)
+{
+    /* Check if kernel supports required UFFD features */
+    if (!ram_write_tracking_available()) {
+        return WT_SUPPORT_ABSENT;
+    }
+    /*
+     * Check if current memory configuration is
+     * compatible with required UFFD features.
+     */
+    if (!ram_write_tracking_compatible()) {
+        return WT_SUPPORT_AVAILABLE;
+    }
+
+    return WT_SUPPORT_COMPATIBLE;
+}
+
+/**
+ * @migration_caps_check - check capability validity
+ *
+ * @cap_list: old capability list, array of bool
+ * @params: new capabilities to be applied soon
+ * @errp: set *errp if the check failed, with reason
+ *
+ * Returns true if check passed, otherwise false.
+ */
+static bool migrate_caps_check(bool *cap_list,
+                               MigrationCapabilityStatusList *params,
+                               Error **errp)
+{
+    MigrationCapabilityStatusList *cap;
+    bool old_postcopy_cap;
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    old_postcopy_cap = cap_list[MIGRATION_CAPABILITY_POSTCOPY_RAM];
+
+    for (cap = params; cap; cap = cap->next) {
+        cap_list[cap->value->capability] = cap->value->state;
+    }
+
+#ifndef CONFIG_LIVE_BLOCK_MIGRATION
+    if (cap_list[MIGRATION_CAPABILITY_BLOCK]) {
+        error_setg(errp, "QEMU compiled without old-style (blk/-b, inc/-i) "
+                   "block migration");
+        error_append_hint(errp, "Use drive_mirror+NBD instead.\n");
+        return false;
+    }
+#endif
+
+#ifndef CONFIG_REPLICATION
+    if (cap_list[MIGRATION_CAPABILITY_X_COLO]) {
+        error_setg(errp, "QEMU compiled without replication module"
+                   " can't enable COLO");
+        error_append_hint(errp, "Please enable replication before COLO.\n");
+        return false;
+    }
+#endif
+
+    if (cap_list[MIGRATION_CAPABILITY_POSTCOPY_RAM]) {
+        /* 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(mis)) {
+            /* postcopy_ram_supported_by_host will have emitted a more
+             * detailed message
+             */
+            error_setg(errp, "Postcopy is not supported");
+            return false;
+        }
+
+        if (cap_list[MIGRATION_CAPABILITY_X_IGNORE_SHARED]) {
+            error_setg(errp, "Postcopy is not compatible with ignore-shared");
+            return false;
+        }
+    }
+
+    if (cap_list[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
+        WriteTrackingSupport wt_support;
+        int idx;
+        /*
+         * Check if 'background-snapshot' capability is supported by
+         * host kernel and compatible with guest memory configuration.
+         */
+        wt_support = migrate_query_write_tracking();
+        if (wt_support < WT_SUPPORT_AVAILABLE) {
+            error_setg(errp, "Background-snapshot is not supported by host kernel");
+            return false;
+        }
+        if (wt_support < WT_SUPPORT_COMPATIBLE) {
+            error_setg(errp, "Background-snapshot is not compatible "
+                    "with guest memory configuration");
+            return false;
+        }
+
+        /*
+         * Check if there are any migration capabilities
+         * incompatible with 'background-snapshot'.
+         */
+        for (idx = 0; idx < check_caps_background_snapshot.size; idx++) {
+            int incomp_cap = check_caps_background_snapshot.caps[idx];
+            if (cap_list[incomp_cap]) {
+                error_setg(errp,
+                        "Background-snapshot is not compatible with %s",
+                        MigrationCapability_str(incomp_cap));
+                return false;
+            }
+        }
+    }
+
+    /* incoming side only */
+    if (runstate_check(RUN_STATE_INMIGRATE) &&
+        !migrate_multifd_is_allowed() &&
+        cap_list[MIGRATION_CAPABILITY_MULTIFD]) {
+        error_setg(errp, "multifd is not supported by current protocol");
+        return false;
+    }
+
+    return true;
+}
+
+static void fill_destination_migration_info(MigrationInfo *info)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (mis->socket_address_list) {
+        info->has_socket_address = true;
+        info->socket_address =
+            QAPI_CLONE(SocketAddressList, mis->socket_address_list);
+    }
+
+    switch (mis->state) {
+    case MIGRATION_STATUS_NONE:
+        return;
+    case MIGRATION_STATUS_SETUP:
+    case MIGRATION_STATUS_CANCELLING:
+    case MIGRATION_STATUS_CANCELLED:
+    case MIGRATION_STATUS_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_PAUSED:
+    case MIGRATION_STATUS_POSTCOPY_RECOVER:
+    case MIGRATION_STATUS_FAILED:
+    case MIGRATION_STATUS_COLO:
+        info->has_status = true;
+        break;
+    case MIGRATION_STATUS_COMPLETED:
+        info->has_status = true;
+        fill_destination_postcopy_migration_info(info);
+        break;
+    }
+    info->status = mis->state;
+}
+
+MigrationInfo *qmp_query_migrate(Error **errp)
+{
+    MigrationInfo *info = g_malloc0(sizeof(*info));
+
+    fill_destination_migration_info(info);
+    fill_source_migration_info(info);
+
+    return info;
+}
+
+void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
+                                  Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+    MigrationCapabilityStatusList *cap;
+    bool cap_list[MIGRATION_CAPABILITY__MAX];
+
+    if (migration_is_running(s->state)) {
+        error_setg(errp, QERR_MIGRATION_ACTIVE);
+        return;
+    }
+
+    memcpy(cap_list, s->enabled_capabilities, sizeof(cap_list));
+    if (!migrate_caps_check(cap_list, params, errp)) {
+        return;
+    }
+
+    for (cap = params; cap; cap = cap->next) {
+        s->enabled_capabilities[cap->value->capability] = cap->value->state;
+    }
+}
+
+/*
+ * Check whether the parameters are valid. Error will be put into errp
+ * (if provided). Return true if valid, otherwise false.
+ */
+static bool migrate_params_check(MigrationParameters *params, Error **errp)
+{
+    if (params->has_compress_level &&
+        (params->compress_level > 9)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "compress_level",
+                   "a value between 0 and 9");
+        return false;
+    }
+
+    if (params->has_compress_threads && (params->compress_threads < 1)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "compress_threads",
+                   "a value between 1 and 255");
+        return false;
+    }
+
+    if (params->has_decompress_threads && (params->decompress_threads < 1)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "decompress_threads",
+                   "a value between 1 and 255");
+        return false;
+    }
+
+    if (params->has_throttle_trigger_threshold &&
+        (params->throttle_trigger_threshold < 1 ||
+         params->throttle_trigger_threshold > 100)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "throttle_trigger_threshold",
+                   "an integer in the range of 1 to 100");
+        return false;
+    }
+
+    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 false;
+    }
+
+    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 false;
+    }
+
+    if (params->has_max_bandwidth && (params->max_bandwidth > SIZE_MAX)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "max_bandwidth",
+                   "an integer in the range of 0 to "stringify(SIZE_MAX)
+                   " bytes/second");
+        return false;
+    }
+
+    if (params->has_downtime_limit &&
+        (params->downtime_limit > MAX_MIGRATE_DOWNTIME)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "downtime_limit",
+                   "an integer in the range of 0 to "
+                    stringify(MAX_MIGRATE_DOWNTIME)" ms");
+        return false;
+    }
+
+    /* x_checkpoint_delay is now always positive */
+
+    if (params->has_multifd_channels && (params->multifd_channels < 1)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "multifd_channels",
+                   "a value between 1 and 255");
+        return false;
+    }
+
+    if (params->has_multifd_zlib_level &&
+        (params->multifd_zlib_level > 9)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "multifd_zlib_level",
+                   "a value between 0 and 9");
+        return false;
+    }
+
+    if (params->has_multifd_zstd_level &&
+        (params->multifd_zstd_level > 20)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "multifd_zstd_level",
+                   "a value between 0 and 20");
+        return false;
+    }
+
+    if (params->has_xbzrle_cache_size &&
+        (params->xbzrle_cache_size < qemu_target_page_size() ||
+         !is_power_of_2(params->xbzrle_cache_size))) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "xbzrle_cache_size",
+                   "a power of two no less than the target page size");
+        return false;
+    }
+
+    if (params->has_max_cpu_throttle &&
+        (params->max_cpu_throttle < params->cpu_throttle_initial ||
+         params->max_cpu_throttle > 99)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "max_cpu_throttle",
+                   "an integer in the range of cpu_throttle_initial to 99");
+        return false;
+    }
+
+    if (params->has_announce_initial &&
+        params->announce_initial > 100000) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "announce_initial",
+                   "a value between 0 and 100000");
+        return false;
+    }
+    if (params->has_announce_max &&
+        params->announce_max > 100000) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "announce_max",
+                   "a value between 0 and 100000");
+       return false;
+    }
+    if (params->has_announce_rounds &&
+        params->announce_rounds > 1000) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "announce_rounds",
+                   "a value between 0 and 1000");
+       return false;
+    }
+    if (params->has_announce_step &&
+        (params->announce_step < 1 ||
+        params->announce_step > 10000)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "announce_step",
+                   "a value between 0 and 10000");
+       return false;
+    }
+
+    if (params->has_block_bitmap_mapping &&
+        !check_dirty_bitmap_mig_alias_map(params->block_bitmap_mapping, errp)) {
+        error_prepend(errp, "Invalid mapping given for block-bitmap-mapping: ");
+        return false;
+    }
+
+    return true;
+}
+
+static void migrate_params_test_apply(MigrateSetParameters *params,
+                                      MigrationParameters *dest)
+{
+    *dest = migrate_get_current()->parameters;
+
+    /* TODO use QAPI_CLONE() instead of duplicating it inline */
+
+    if (params->has_compress_level) {
+        dest->compress_level = params->compress_level;
+    }
+
+    if (params->has_compress_threads) {
+        dest->compress_threads = params->compress_threads;
+    }
+
+    if (params->has_compress_wait_thread) {
+        dest->compress_wait_thread = params->compress_wait_thread;
+    }
+
+    if (params->has_decompress_threads) {
+        dest->decompress_threads = params->decompress_threads;
+    }
+
+    if (params->has_throttle_trigger_threshold) {
+        dest->throttle_trigger_threshold = params->throttle_trigger_threshold;
+    }
+
+    if (params->has_cpu_throttle_initial) {
+        dest->cpu_throttle_initial = params->cpu_throttle_initial;
+    }
+
+    if (params->has_cpu_throttle_increment) {
+        dest->cpu_throttle_increment = params->cpu_throttle_increment;
+    }
+
+    if (params->has_cpu_throttle_tailslow) {
+        dest->cpu_throttle_tailslow = params->cpu_throttle_tailslow;
+    }
+
+    if (params->has_tls_creds) {
+        assert(params->tls_creds->type == QTYPE_QSTRING);
+        dest->tls_creds = params->tls_creds->u.s;
+    }
+
+    if (params->has_tls_hostname) {
+        assert(params->tls_hostname->type == QTYPE_QSTRING);
+        dest->tls_hostname = params->tls_hostname->u.s;
+    }
+
+    if (params->has_max_bandwidth) {
+        dest->max_bandwidth = params->max_bandwidth;
+    }
+
+    if (params->has_downtime_limit) {
+        dest->downtime_limit = params->downtime_limit;
+    }
+
+    if (params->has_x_checkpoint_delay) {
+        dest->x_checkpoint_delay = params->x_checkpoint_delay;
+    }
+
+    if (params->has_block_incremental) {
+        dest->block_incremental = params->block_incremental;
+    }
+    if (params->has_multifd_channels) {
+        dest->multifd_channels = params->multifd_channels;
+    }
+    if (params->has_multifd_compression) {
+        dest->multifd_compression = params->multifd_compression;
+    }
+    if (params->has_xbzrle_cache_size) {
+        dest->xbzrle_cache_size = params->xbzrle_cache_size;
+    }
+    if (params->has_max_postcopy_bandwidth) {
+        dest->max_postcopy_bandwidth = params->max_postcopy_bandwidth;
+    }
+    if (params->has_max_cpu_throttle) {
+        dest->max_cpu_throttle = params->max_cpu_throttle;
+    }
+    if (params->has_announce_initial) {
+        dest->announce_initial = params->announce_initial;
+    }
+    if (params->has_announce_max) {
+        dest->announce_max = params->announce_max;
+    }
+    if (params->has_announce_rounds) {
+        dest->announce_rounds = params->announce_rounds;
+    }
+    if (params->has_announce_step) {
+        dest->announce_step = params->announce_step;
+    }
+
+    if (params->has_block_bitmap_mapping) {
+        dest->has_block_bitmap_mapping = true;
+        dest->block_bitmap_mapping = params->block_bitmap_mapping;
+    }
+}
+
+static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+
+    /* TODO use QAPI_CLONE() instead of duplicating it inline */
+
+    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_compress_wait_thread) {
+        s->parameters.compress_wait_thread = params->compress_wait_thread;
+    }
+
+    if (params->has_decompress_threads) {
+        s->parameters.decompress_threads = params->decompress_threads;
+    }
+
+    if (params->has_throttle_trigger_threshold) {
+        s->parameters.throttle_trigger_threshold = params->throttle_trigger_threshold;
+    }
+
+    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_cpu_throttle_tailslow) {
+        s->parameters.cpu_throttle_tailslow = params->cpu_throttle_tailslow;
+    }
+
+    if (params->has_tls_creds) {
+        g_free(s->parameters.tls_creds);
+        assert(params->tls_creds->type == QTYPE_QSTRING);
+        s->parameters.tls_creds = g_strdup(params->tls_creds->u.s);
+    }
+
+    if (params->has_tls_hostname) {
+        g_free(s->parameters.tls_hostname);
+        assert(params->tls_hostname->type == QTYPE_QSTRING);
+        s->parameters.tls_hostname = g_strdup(params->tls_hostname->u.s);
+    }
+
+    if (params->has_tls_authz) {
+        g_free(s->parameters.tls_authz);
+        assert(params->tls_authz->type == QTYPE_QSTRING);
+        s->parameters.tls_authz = g_strdup(params->tls_authz->u.s);
+    }
+
+    if (params->has_max_bandwidth) {
+        s->parameters.max_bandwidth = params->max_bandwidth;
+        if (s->to_dst_file && !migration_in_postcopy()) {
+            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;
+    }
+    if (params->has_multifd_channels) {
+        s->parameters.multifd_channels = params->multifd_channels;
+    }
+    if (params->has_multifd_compression) {
+        s->parameters.multifd_compression = params->multifd_compression;
+    }
+    if (params->has_xbzrle_cache_size) {
+        s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
+        xbzrle_cache_resize(params->xbzrle_cache_size, errp);
+    }
+    if (params->has_max_postcopy_bandwidth) {
+        s->parameters.max_postcopy_bandwidth = params->max_postcopy_bandwidth;
+        if (s->to_dst_file && migration_in_postcopy()) {
+            qemu_file_set_rate_limit(s->to_dst_file,
+                    s->parameters.max_postcopy_bandwidth / XFER_LIMIT_RATIO);
+        }
+    }
+    if (params->has_max_cpu_throttle) {
+        s->parameters.max_cpu_throttle = params->max_cpu_throttle;
+    }
+    if (params->has_announce_initial) {
+        s->parameters.announce_initial = params->announce_initial;
+    }
+    if (params->has_announce_max) {
+        s->parameters.announce_max = params->announce_max;
+    }
+    if (params->has_announce_rounds) {
+        s->parameters.announce_rounds = params->announce_rounds;
+    }
+    if (params->has_announce_step) {
+        s->parameters.announce_step = params->announce_step;
+    }
+
+    if (params->has_block_bitmap_mapping) {
+        qapi_free_BitmapMigrationNodeAliasList(
+            s->parameters.block_bitmap_mapping);
+
+        s->parameters.has_block_bitmap_mapping = true;
+        s->parameters.block_bitmap_mapping =
+            QAPI_CLONE(BitmapMigrationNodeAliasList,
+                       params->block_bitmap_mapping);
+    }
+}
+
+void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
+{
+    MigrationParameters tmp;
+
+    /* TODO Rewrite "" to null instead */
+    if (params->has_tls_creds
+        && params->tls_creds->type == QTYPE_QNULL) {
+        qobject_unref(params->tls_creds->u.n);
+        params->tls_creds->type = QTYPE_QSTRING;
+        params->tls_creds->u.s = strdup("");
+    }
+    /* TODO Rewrite "" to null instead */
+    if (params->has_tls_hostname
+        && params->tls_hostname->type == QTYPE_QNULL) {
+        qobject_unref(params->tls_hostname->u.n);
+        params->tls_hostname->type = QTYPE_QSTRING;
+        params->tls_hostname->u.s = strdup("");
+    }
+
+    migrate_params_test_apply(params, &tmp);
+
+    if (!migrate_params_check(&tmp, errp)) {
+        /* Invalid parameter */
+        return;
+    }
+
+    migrate_params_apply(params, errp);
+}
+
+
+void qmp_migrate_start_postcopy(Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+
+    if (!migrate_postcopy()) {
+        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.
+     */
+    qatomic_set(&s->start_postcopy, true);
+}
+
+/* shared migration helpers */
+
+void migrate_set_state(int *state, int old_state, int new_state)
+{
+    assert(new_state < MIGRATION_STATUS__MAX);
+    if (qatomic_cmpxchg(state, old_state, new_state) == old_state) {
+        trace_migrate_set_state(MigrationStatus_str(new_state));
+        migrate_generate_event(new_state);
+    }
+}
+
+static MigrationCapabilityStatus *migrate_cap_add(MigrationCapability index,
+                                                  bool state)
+{
+    MigrationCapabilityStatus *cap;
+
+    cap = g_new0(MigrationCapabilityStatus, 1);
+    cap->capability = index;
+    cap->state = state;
+
+    return cap;
+}
+
+void migrate_set_block_enabled(bool value, Error **errp)
+{
+    MigrationCapabilityStatusList *cap = NULL;
+
+    QAPI_LIST_PREPEND(cap, migrate_cap_add(MIGRATION_CAPABILITY_BLOCK, 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(MigrationState *s)
+{
+    qemu_bh_delete(s->cleanup_bh);
+    s->cleanup_bh = NULL;
+
+    qemu_savevm_state_cleanup();
+
+    if (s->to_dst_file) {
+        QEMUFile *tmp;
+
+        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();
+
+        multifd_save_cleanup();
+        qemu_mutex_lock(&s->qemu_file_lock);
+        tmp = s->to_dst_file;
+        s->to_dst_file = NULL;
+        qemu_mutex_unlock(&s->qemu_file_lock);
+        /*
+         * Close the file handle without the lock to make sure the
+         * critical section won't block for long.
+         */
+        migration_ioc_unregister_yank_from_file(tmp);
+        qemu_fclose(tmp);
+    }
+
+    assert(!migration_is_active(s));
+
+    if (s->state == MIGRATION_STATUS_CANCELLING) {
+        migrate_set_state(&s->state, MIGRATION_STATUS_CANCELLING,
+                          MIGRATION_STATUS_CANCELLED);
+    }
+
+    if (s->error) {
+        /* It is used on info migrate.  We can't free it */
+        error_report_err(error_copy(s->error));
+    }
+    notifier_list_notify(&migration_state_notifiers, s);
+    block_cleanup_parameters(s);
+    yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+}
+
+static void migrate_fd_cleanup_schedule(MigrationState *s)
+{
+    /*
+     * Ref the state for bh, because it may be called when
+     * there're already no other refs
+     */
+    object_ref(OBJECT(s));
+    qemu_bh_schedule(s->cleanup_bh);
+}
+
+static void migrate_fd_cleanup_bh(void *opaque)
+{
+    MigrationState *s = opaque;
+    migrate_fd_cleanup(s);
+    object_unref(OBJECT(s));
+}
+
+void migrate_set_error(MigrationState *s, const Error *error)
+{
+    QEMU_LOCK_GUARD(&s->error_mutex);
+    if (!s->error) {
+        s->error = error_copy(error);
+    }
+}
+
+static void migrate_error_free(MigrationState *s)
+{
+    QEMU_LOCK_GUARD(&s->error_mutex);
+    if (s->error) {
+        error_free(s->error);
+        s->error = NULL;
+    }
+}
+
+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);
+    migrate_set_error(s, error);
+}
+
+static void migrate_fd_cancel(MigrationState *s)
+{
+    int old_state ;
+    QEMUFile *f = migrate_get_current()->to_dst_file;
+    trace_migrate_fd_cancel();
+
+    WITH_QEMU_LOCK_GUARD(&s->qemu_file_lock) {
+        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_running(old_state)) {
+            break;
+        }
+        /* If the migration is paused, kick it out of the pause */
+        if (old_state == MIGRATION_STATUS_PRE_SWITCHOVER) {
+            qemu_sem_post(&s->pause_sem);
+        }
+        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;
+        }
+    }
+}
+
+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();
+
+    switch (s->state) {
+    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
+    case MIGRATION_STATUS_POSTCOPY_PAUSED:
+    case MIGRATION_STATUS_POSTCOPY_RECOVER:
+        return true;
+    default:
+        return false;
+    }
+}
+
+bool migration_in_postcopy_after_devices(MigrationState *s)
+{
+    return migration_in_postcopy() && s->postcopy_after_devices;
+}
+
+bool migration_in_incoming_postcopy(void)
+{
+    PostcopyState ps = postcopy_state_get();
+
+    return ps >= POSTCOPY_INCOMING_DISCARD && ps < POSTCOPY_INCOMING_END;
+}
+
+bool migration_in_bg_snapshot(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return migrate_background_snapshot() &&
+            migration_is_setup_or_active(s->state);
+}
+
+bool migration_is_idle(void)
+{
+    MigrationState *s = current_migration;
+
+    if (!s) {
+        return true;
+    }
+
+    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:
+    case MIGRATION_STATUS_PRE_SWITCHOVER:
+    case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_WAIT_UNPLUG:
+        return false;
+    case MIGRATION_STATUS__MAX:
+        g_assert_not_reached();
+    }
+
+    return false;
+}
+
+bool migration_is_active(MigrationState *s)
+{
+    return (s->state == MIGRATION_STATUS_ACTIVE ||
+            s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
+}
+
+void migrate_init(MigrationState *s)
+{
+    /*
+     * Reinitialise all migration state, except
+     * parameters/capabilities that the user set, and
+     * locks.
+     */
+    s->cleanup_bh = 0;
+    s->vm_start_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->pages_per_second = 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;
+    s->hostname = NULL;
+
+    migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);
+
+    s->start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    s->total_time = 0;
+    s->vm_was_running = false;
+    s->iteration_initial_bytes = 0;
+    s->threshold_size = 0;
+}
+
+int migrate_add_blocker_internal(Error *reason, Error **errp)
+{
+    /* Snapshots are similar to migrations, so check RUN_STATE_SAVE_VM too. */
+    if (runstate_check(RUN_STATE_SAVE_VM) || !migration_is_idle()) {
+        error_propagate_prepend(errp, error_copy(reason),
+                                "disallowing migration blocker "
+                                "(migration/snapshot in progress) for: ");
+        return -EBUSY;
+    }
+
+    migration_blockers = g_slist_prepend(migration_blockers, reason);
+    return 0;
+}
+
+int migrate_add_blocker(Error *reason, Error **errp)
+{
+    if (only_migratable) {
+        error_propagate_prepend(errp, error_copy(reason),
+                                "disallowing migration blocker "
+                                "(--only-migratable) for: ");
+        return -EACCES;
+    }
+
+    return migrate_add_blocker_internal(reason, errp);
+}
+
+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 (!once) {
+        error_setg(errp, "The incoming migration has already been started");
+        return;
+    }
+    if (!runstate_check(RUN_STATE_INMIGRATE)) {
+        error_setg(errp, "'-incoming' was not specified on the command line");
+        return;
+    }
+
+    if (!yank_register_instance(MIGRATION_YANK_INSTANCE, errp)) {
+        return;
+    }
+
+    qemu_start_incoming_migration(uri, &local_err);
+
+    if (local_err) {
+        yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    once = false;
+}
+
+void qmp_migrate_recover(const char *uri, Error **errp)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    /*
+     * Don't even bother to use ERRP_GUARD() as it _must_ always be set by
+     * callers (no one should ignore a recover failure); if there is, it's a
+     * programming error.
+     */
+    assert(errp);
+
+    if (mis->state != MIGRATION_STATUS_POSTCOPY_PAUSED) {
+        error_setg(errp, "Migrate recover can only be run "
+                   "when postcopy is paused.");
+        return;
+    }
+
+    if (qatomic_cmpxchg(&mis->postcopy_recover_triggered,
+                       false, true) == true) {
+        error_setg(errp, "Migrate recovery is triggered already");
+        return;
+    }
+
+    /*
+     * Note that this call will never start a real migration; it will
+     * only re-setup the migration stream and poke existing migration
+     * to continue using that newly established channel.
+     */
+    qemu_start_incoming_migration(uri, errp);
+
+    /* Safe to dereference with the assert above */
+    if (*errp) {
+        /* Reset the flag so user could still retry */
+        qatomic_set(&mis->postcopy_recover_triggered, false);
+    }
+}
+
+void qmp_migrate_pause(Error **errp)
+{
+    MigrationState *ms = migrate_get_current();
+    MigrationIncomingState *mis = migration_incoming_get_current();
+    int ret;
+
+    if (ms->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
+        /* Source side, during postcopy */
+        qemu_mutex_lock(&ms->qemu_file_lock);
+        ret = qemu_file_shutdown(ms->to_dst_file);
+        qemu_mutex_unlock(&ms->qemu_file_lock);
+        if (ret) {
+            error_setg(errp, "Failed to pause source migration");
+        }
+        return;
+    }
+
+    if (mis->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
+        ret = qemu_file_shutdown(mis->from_src_file);
+        if (ret) {
+            error_setg(errp, "Failed to pause destination migration");
+        }
+        return;
+    }
+
+    error_setg(errp, "migrate-pause is currently only supported "
+               "during postcopy-active state");
+}
+
+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;
+}
+
+/* Returns true if continue to migrate, or false if error detected */
+static bool migrate_prepare(MigrationState *s, bool blk, bool blk_inc,
+                            bool resume, Error **errp)
+{
+    Error *local_err = NULL;
+
+    if (resume) {
+        if (s->state != MIGRATION_STATUS_POSTCOPY_PAUSED) {
+            error_setg(errp, "Cannot resume if there is no "
+                       "paused migration");
+            return false;
+        }
+
+        /*
+         * Postcopy recovery won't work well with release-ram
+         * capability since release-ram will drop the page buffer as
+         * long as the page is put into the send buffer.  So if there
+         * is a network failure happened, any page buffers that have
+         * not yet reached the destination VM but have already been
+         * sent from the source VM will be lost forever.  Let's refuse
+         * the client from resuming such a postcopy migration.
+         * Luckily release-ram was designed to only be used when src
+         * and destination VMs are on the same host, so it should be
+         * fine.
+         */
+        if (migrate_release_ram()) {
+            error_setg(errp, "Postcopy recovery cannot work "
+                       "when release-ram capability is set");
+            return false;
+        }
+
+        /* This is a resume, skip init status */
+        return true;
+    }
+
+    if (migration_is_running(s->state)) {
+        error_setg(errp, QERR_MIGRATION_ACTIVE);
+        return false;
+    }
+
+    if (runstate_check(RUN_STATE_INMIGRATE)) {
+        error_setg(errp, "Guest is waiting for an incoming migration");
+        return false;
+    }
+
+    if (runstate_check(RUN_STATE_POSTMIGRATE)) {
+        error_setg(errp, "Can't migrate the vm that was paused due to "
+                   "previous migration");
+        return false;
+    }
+
+    if (migration_is_blocked(errp)) {
+        return false;
+    }
+
+    if (blk || blk_inc) {
+        if (migrate_colo_enabled()) {
+            error_setg(errp, "No disk migration is required in COLO mode");
+            return false;
+        }
+        if (migrate_use_block() || migrate_use_block_incremental()) {
+            error_setg(errp, "Command options are incompatible with "
+                       "current migration capabilities");
+            return false;
+        }
+        migrate_set_block_enabled(true, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return false;
+        }
+        s->must_remove_block_options = true;
+    }
+
+    if (blk_inc) {
+        migrate_set_block_incremental(s, true);
+    }
+
+    migrate_init(s);
+    /*
+     * set ram_counters compression_counters memory to zero for a
+     * new migration
+     */
+    memset(&ram_counters, 0, sizeof(ram_counters));
+    memset(&compression_counters, 0, sizeof(compression_counters));
+
+    return true;
+}
+
+void qmp_migrate(const char *uri, bool has_blk, bool blk,
+                 bool has_inc, bool inc, bool has_detach, bool detach,
+                 bool has_resume, bool resume, Error **errp)
+{
+    Error *local_err = NULL;
+    MigrationState *s = migrate_get_current();
+    const char *p = NULL;
+
+    if (!migrate_prepare(s, has_blk && blk, has_inc && inc,
+                         has_resume && resume, errp)) {
+        /* Error detected, put into errp */
+        return;
+    }
+
+    if (!(has_resume && resume)) {
+        if (!yank_register_instance(MIGRATION_YANK_INSTANCE, errp)) {
+            return;
+        }
+    }
+
+    migrate_protocol_allow_multifd(false);
+    if (strstart(uri, "tcp:", &p) ||
+        strstart(uri, "unix:", NULL) ||
+        strstart(uri, "vsock:", NULL)) {
+        migrate_protocol_allow_multifd(true);
+        socket_start_outgoing_migration(s, p ? p : uri, &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, "fd:", &p)) {
+        fd_start_outgoing_migration(s, p, &local_err);
+    } else {
+        if (!(has_resume && resume)) {
+            yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+        }
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "uri",
+                   "a valid migration protocol");
+        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                          MIGRATION_STATUS_FAILED);
+        block_cleanup_parameters(s);
+        return;
+    }
+
+    if (local_err) {
+        if (!(has_resume && resume)) {
+            yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+        }
+        migrate_fd_error(s, local_err);
+        error_propagate(errp, local_err);
+        return;
+    }
+}
+
+void qmp_migrate_cancel(Error **errp)
+{
+    migration_cancel(NULL);
+}
+
+void qmp_migrate_continue(MigrationStatus state, Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+    if (s->state != state) {
+        error_setg(errp,  "Migration not in expected state: %s",
+                   MigrationStatus_str(s->state));
+        return;
+    }
+    qemu_sem_post(&s->pause_sem);
+}
+
+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_postcopy(void)
+{
+    return migrate_postcopy_ram() || migrate_dirty_bitmaps();
+}
+
+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_postcopy_blocktime(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_BLOCKTIME];
+}
+
+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_compress_wait_thread(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.compress_wait_thread;
+}
+
+int migrate_decompress_threads(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.decompress_threads;
+}
+
+bool migrate_dirty_bitmaps(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_DIRTY_BITMAPS];
+}
+
+bool migrate_ignore_shared(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_X_IGNORE_SHARED];
+}
+
+bool migrate_validate_uuid(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_VALIDATE_UUID];
+}
+
+bool migrate_use_events(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_EVENTS];
+}
+
+bool migrate_use_multifd(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD];
+}
+
+bool migrate_pause_before_switchover(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[
+        MIGRATION_CAPABILITY_PAUSE_BEFORE_SWITCHOVER];
+}
+
+int migrate_multifd_channels(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.multifd_channels;
+}
+
+MultiFDCompression migrate_multifd_compression(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.multifd_compression;
+}
+
+int migrate_multifd_zlib_level(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.multifd_zlib_level;
+}
+
+int migrate_multifd_zstd_level(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.multifd_zstd_level;
+}
+
+int migrate_use_xbzrle(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_XBZRLE];
+}
+
+uint64_t migrate_xbzrle_cache_size(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.xbzrle_cache_size;
+}
+
+static int64_t migrate_max_postcopy_bandwidth(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.max_postcopy_bandwidth;
+}
+
+bool migrate_use_block(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_BLOCK];
+}
+
+bool migrate_use_return_path(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_RETURN_PATH];
+}
+
+bool migrate_use_block_incremental(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.block_incremental;
+}
+
+bool migrate_background_snapshot(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT];
+}
+
+/* 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_RECV_BITMAP]    = { .len = -1, .name = "RECV_BITMAP" },
+    [MIG_RP_MSG_RESUME_ACK]     = { .len =  4, .name = "RESUME_ACK" },
+    [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 = qemu_real_host_page_size;
+
+    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 (!QEMU_IS_ALIGNED(start, our_host_ps) ||
+        !QEMU_IS_ALIGNED(len, our_host_ps)) {
+        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);
+    }
+}
+
+/* Return true to retry, false to quit */
+static bool postcopy_pause_return_path_thread(MigrationState *s)
+{
+    trace_postcopy_pause_return_path();
+
+    qemu_sem_wait(&s->postcopy_pause_rp_sem);
+
+    trace_postcopy_pause_return_path_continued();
+
+    return true;
+}
+
+static int migrate_handle_rp_recv_bitmap(MigrationState *s, char *block_name)
+{
+    RAMBlock *block = qemu_ram_block_by_name(block_name);
+
+    if (!block) {
+        error_report("%s: invalid block name '%s'", __func__, block_name);
+        return -EINVAL;
+    }
+
+    /* Fetch the received bitmap and refresh the dirty bitmap */
+    return ram_dirty_bitmap_reload(s, block);
+}
+
+static int migrate_handle_rp_resume_ack(MigrationState *s, uint32_t value)
+{
+    trace_source_return_path_thread_resume_ack(value);
+
+    if (value != MIGRATION_RESUME_ACK_VALUE) {
+        error_report("%s: illegal resume_ack value %"PRIu32,
+                     __func__, value);
+        return -1;
+    }
+
+    /* Now both sides are active. */
+    migrate_set_state(&s->state, MIGRATION_STATUS_POSTCOPY_RECOVER,
+                      MIGRATION_STATUS_POSTCOPY_ACTIVE);
+
+    /* Notify send thread that time to continue send pages */
+    qemu_sem_post(&s->rp_state.rp_sem);
+
+    return 0;
+}
+
+/* Release ms->rp_state.from_dst_file in a safe way */
+static void migration_release_from_dst_file(MigrationState *ms)
+{
+    QEMUFile *file;
+
+    WITH_QEMU_LOCK_GUARD(&ms->qemu_file_lock) {
+        /*
+         * Reset the from_dst_file pointer first before releasing it, as we
+         * can't block within lock section
+         */
+        file = ms->rp_state.from_dst_file;
+        ms->rp_state.from_dst_file = NULL;
+    }
+
+    qemu_fclose(file);
+}
+
+/*
+ * 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();
+    rcu_register_thread();
+
+retry:
+    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 (qemu_file_get_error(rp)) {
+            mark_source_rp_bad(ms);
+            goto out;
+        }
+
+        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;
+
+        case MIG_RP_MSG_RECV_BITMAP:
+            if (header_len < 1) {
+                error_report("%s: missing block name", __func__);
+                mark_source_rp_bad(ms);
+                goto out;
+            }
+            /* Format: len (1B) + idstr (<255B). This ends the idstr. */
+            buf[buf[0] + 1] = '\0';
+            if (migrate_handle_rp_recv_bitmap(ms, (char *)(buf + 1))) {
+                mark_source_rp_bad(ms);
+                goto out;
+            }
+            break;
+
+        case MIG_RP_MSG_RESUME_ACK:
+            tmp32 = ldl_be_p(buf);
+            if (migrate_handle_rp_resume_ack(ms, tmp32)) {
+                mark_source_rp_bad(ms);
+                goto out;
+            }
+            break;
+
+        default:
+            break;
+        }
+    }
+
+out:
+    res = qemu_file_get_error(rp);
+    if (res) {
+        if (res == -EIO && migration_in_postcopy()) {
+            /*
+             * Maybe there is something we can do: it looks like a
+             * network down issue, and we pause for a recovery.
+             */
+            migration_release_from_dst_file(ms);
+            rp = NULL;
+            if (postcopy_pause_return_path_thread(ms)) {
+                /*
+                 * Reload rp, reset the rest.  Referencing it is safe since
+                 * it's reset only by us above, or when migration completes
+                 */
+                rp = ms->rp_state.from_dst_file;
+                ms->rp_state.error = false;
+                goto retry;
+            }
+        }
+
+        trace_source_return_path_thread_bad_end();
+        mark_source_rp_bad(ms);
+    }
+
+    trace_source_return_path_thread_end();
+    migration_release_from_dst_file(ms);
+    rcu_unregister_thread();
+    return NULL;
+}
+
+static int open_return_path_on_source(MigrationState *ms,
+                                      bool create_thread)
+{
+    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();
+
+    if (!create_thread) {
+        /* We're done */
+        return 0;
+    }
+
+    qemu_thread_create(&ms->rp_state.rp_thread, "return path",
+                       source_return_path_thread, ms, QEMU_THREAD_JOINABLE);
+    ms->rp_state.rp_thread_created = true;
+
+    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);
+    ms->rp_state.rp_thread_created = false;
+    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)
+{
+    int ret;
+    QIOChannelBuffer *bioc;
+    QEMUFile *fb;
+    int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    int64_t bandwidth = migrate_max_postcopy_bandwidth();
+    bool restart_block = false;
+    int cur_state = MIGRATION_STATUS_ACTIVE;
+    if (!migrate_pause_before_switchover()) {
+        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, NULL);
+    global_state_store();
+    ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = migration_maybe_pause(ms, &cur_state,
+                                MIGRATION_STATUS_POSTCOPY_ACTIVE);
+    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, false);
+
+    /*
+     * 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 (migrate_postcopy_ram()) {
+        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
+     */
+    /* 0 max-postcopy-bandwidth means unlimited */
+    if (!bandwidth) {
+        qemu_file_set_rate_limit(ms->to_dst_file, INT64_MAX);
+    } else {
+        qemu_file_set_rate_limit(ms->to_dst_file, bandwidth / XFER_LIMIT_RATIO);
+    }
+    if (migrate_postcopy_ram()) {
+        /* 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, false);
+    if (migrate_postcopy_ram()) {
+        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();
+
+    if (migrate_postcopy_ram()) {
+        /*
+         * 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_maybe_pause: Pause if required to by
+ * migrate_pause_before_switchover called with the iothread locked
+ * Returns: 0 on success
+ */
+static int migration_maybe_pause(MigrationState *s,
+                                 int *current_active_state,
+                                 int new_state)
+{
+    if (!migrate_pause_before_switchover()) {
+        return 0;
+    }
+
+    /* Since leaving this state is not atomic with posting the semaphore
+     * it's possible that someone could have issued multiple migrate_continue
+     * and the semaphore is incorrectly positive at this point;
+     * the docs say it's undefined to reinit a semaphore that's already
+     * init'd, so use timedwait to eat up any existing posts.
+     */
+    while (qemu_sem_timedwait(&s->pause_sem, 1) == 0) {
+        /* This block intentionally left blank */
+    }
+
+    /*
+     * If the migration is cancelled when it is in the completion phase,
+     * the migration state is set to MIGRATION_STATUS_CANCELLING.
+     * So we don't need to wait a semaphore, otherwise we would always
+     * wait for the 'pause_sem' semaphore.
+     */
+    if (s->state != MIGRATION_STATUS_CANCELLING) {
+        qemu_mutex_unlock_iothread();
+        migrate_set_state(&s->state, *current_active_state,
+                          MIGRATION_STATUS_PRE_SWITCHOVER);
+        qemu_sem_wait(&s->pause_sem);
+        migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER,
+                          new_state);
+        *current_active_state = new_state;
+        qemu_mutex_lock_iothread();
+    }
+
+    return s->state == new_state ? 0 : -EINVAL;
+}
+
+/**
+ * migration_completion: Used by migration_thread when there's not much left.
+ *   The caller 'breaks' the loop when this returns.
+ *
+ * @s: Current migration state
+ */
+static void migration_completion(MigrationState *s)
+{
+    int ret;
+    int current_active_state = s->state;
+
+    if (s->state == MIGRATION_STATUS_ACTIVE) {
+        qemu_mutex_lock_iothread();
+        s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
+        s->vm_was_running = runstate_is_running();
+        ret = global_state_store();
+
+        if (!ret) {
+            bool inactivate = !migrate_colo_enabled();
+            ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
+            trace_migration_completion_vm_stop(ret);
+            if (ret >= 0) {
+                ret = migration_maybe_pause(s, &current_active_state,
+                                            MIGRATION_STATUS_DEVICE);
+            }
+            if (ret >= 0) {
+                qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX);
+                ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false,
+                                                         inactivate);
+            }
+            if (inactivate && 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_mutex_lock_iothread();
+        qemu_savevm_state_complete_postcopy(s->to_dst_file);
+        qemu_mutex_unlock_iothread();
+
+        trace_migration_completion_postcopy_end_after_complete();
+    } else if (s->state == MIGRATION_STATUS_CANCELLING) {
+        goto fail;
+    }
+
+    /*
+     * 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.rp_thread_created) {
+        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 ||
+        s->state == MIGRATION_STATUS_DEVICE) {
+        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);
+}
+
+/**
+ * bg_migration_completion: Used by bg_migration_thread when after all the
+ *   RAM has been saved. The caller 'breaks' the loop when this returns.
+ *
+ * @s: Current migration state
+ */
+static void bg_migration_completion(MigrationState *s)
+{
+    int current_active_state = s->state;
+
+    /*
+     * Stop tracking RAM writes - un-protect memory, un-register UFFD
+     * memory ranges, flush kernel wait queues and wake up threads
+     * waiting for write fault to be resolved.
+     */
+    ram_write_tracking_stop();
+
+    if (s->state == MIGRATION_STATUS_ACTIVE) {
+        /*
+         * By this moment we have RAM content saved into the migration stream.
+         * The next step is to flush the non-RAM content (device state)
+         * right after the ram content. The device state has been stored into
+         * the temporary buffer before RAM saving started.
+         */
+        qemu_put_buffer(s->to_dst_file, s->bioc->data, s->bioc->usage);
+        qemu_fflush(s->to_dst_file);
+    } else if (s->state == MIGRATION_STATUS_CANCELLING) {
+        goto fail;
+    }
+
+    if (qemu_file_get_error(s->to_dst_file)) {
+        trace_migration_completion_file_err();
+        goto fail;
+    }
+
+    migrate_set_state(&s->state, current_active_state,
+                      MIGRATION_STATUS_COMPLETED);
+    return;
+
+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];
+}
+
+typedef enum MigThrError {
+    /* No error detected */
+    MIG_THR_ERR_NONE = 0,
+    /* Detected error, but resumed successfully */
+    MIG_THR_ERR_RECOVERED = 1,
+    /* Detected fatal error, need to exit */
+    MIG_THR_ERR_FATAL = 2,
+} MigThrError;
+
+static int postcopy_resume_handshake(MigrationState *s)
+{
+    qemu_savevm_send_postcopy_resume(s->to_dst_file);
+
+    while (s->state == MIGRATION_STATUS_POSTCOPY_RECOVER) {
+        qemu_sem_wait(&s->rp_state.rp_sem);
+    }
+
+    if (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
+        return 0;
+    }
+
+    return -1;
+}
+
+/* Return zero if success, or <0 for error */
+static int postcopy_do_resume(MigrationState *s)
+{
+    int ret;
+
+    /*
+     * Call all the resume_prepare() hooks, so that modules can be
+     * ready for the migration resume.
+     */
+    ret = qemu_savevm_state_resume_prepare(s);
+    if (ret) {
+        error_report("%s: resume_prepare() failure detected: %d",
+                     __func__, ret);
+        return ret;
+    }
+
+    /*
+     * Last handshake with destination on the resume (destination will
+     * switch to postcopy-active afterwards)
+     */
+    ret = postcopy_resume_handshake(s);
+    if (ret) {
+        error_report("%s: handshake failed: %d", __func__, ret);
+        return ret;
+    }
+
+    return 0;
+}
+
+/*
+ * We don't return until we are in a safe state to continue current
+ * postcopy migration.  Returns MIG_THR_ERR_RECOVERED if recovered, or
+ * MIG_THR_ERR_FATAL if unrecovery failure happened.
+ */
+static MigThrError postcopy_pause(MigrationState *s)
+{
+    assert(s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
+
+    while (true) {
+        QEMUFile *file;
+
+        /*
+         * Current channel is possibly broken. Release it.  Note that this is
+         * guaranteed even without lock because to_dst_file should only be
+         * modified by the migration thread.  That also guarantees that the
+         * unregister of yank is safe too without the lock.  It should be safe
+         * even to be within the qemu_file_lock, but we didn't do that to avoid
+         * taking more mutex (yank_lock) within qemu_file_lock.  TL;DR: we make
+         * the qemu_file_lock critical section as small as possible.
+         */
+        assert(s->to_dst_file);
+        migration_ioc_unregister_yank_from_file(s->to_dst_file);
+        qemu_mutex_lock(&s->qemu_file_lock);
+        file = s->to_dst_file;
+        s->to_dst_file = NULL;
+        qemu_mutex_unlock(&s->qemu_file_lock);
+
+        qemu_file_shutdown(file);
+        qemu_fclose(file);
+
+        migrate_set_state(&s->state, s->state,
+                          MIGRATION_STATUS_POSTCOPY_PAUSED);
+
+        error_report("Detected IO failure for postcopy. "
+                     "Migration paused.");
+
+        /*
+         * We wait until things fixed up. Then someone will setup the
+         * status back for us.
+         */
+        while (s->state == MIGRATION_STATUS_POSTCOPY_PAUSED) {
+            qemu_sem_wait(&s->postcopy_pause_sem);
+        }
+
+        if (s->state == MIGRATION_STATUS_POSTCOPY_RECOVER) {
+            /* Woken up by a recover procedure. Give it a shot */
+
+            /*
+             * Firstly, let's wake up the return path now, with a new
+             * return path channel.
+             */
+            qemu_sem_post(&s->postcopy_pause_rp_sem);
+
+            /* Do the resume logic */
+            if (postcopy_do_resume(s) == 0) {
+                /* Let's continue! */
+                trace_postcopy_pause_continued();
+                return MIG_THR_ERR_RECOVERED;
+            } else {
+                /*
+                 * Something wrong happened during the recovery, let's
+                 * pause again. Pause is always better than throwing
+                 * data away.
+                 */
+                continue;
+            }
+        } else {
+            /* This is not right... Time to quit. */
+            return MIG_THR_ERR_FATAL;
+        }
+    }
+}
+
+static MigThrError migration_detect_error(MigrationState *s)
+{
+    int ret;
+    int state = s->state;
+    Error *local_error = NULL;
+
+    if (state == MIGRATION_STATUS_CANCELLING ||
+        state == MIGRATION_STATUS_CANCELLED) {
+        /* End the migration, but don't set the state to failed */
+        return MIG_THR_ERR_FATAL;
+    }
+
+    /* Try to detect any file errors */
+    ret = qemu_file_get_error_obj(s->to_dst_file, &local_error);
+    if (!ret) {
+        /* Everything is fine */
+        assert(!local_error);
+        return MIG_THR_ERR_NONE;
+    }
+
+    if (local_error) {
+        migrate_set_error(s, local_error);
+        error_free(local_error);
+    }
+
+    if (state == MIGRATION_STATUS_POSTCOPY_ACTIVE && ret == -EIO) {
+        /*
+         * For postcopy, we allow the network to be down for a
+         * while. After that, it can be continued by a
+         * recovery phase.
+         */
+        return postcopy_pause(s);
+    } else {
+        /*
+         * For precopy (or postcopy with error outside IO), we fail
+         * with no time.
+         */
+        migrate_set_state(&s->state, state, MIGRATION_STATUS_FAILED);
+        trace_migration_thread_file_err();
+
+        /* Time to stop the migration, now. */
+        return MIG_THR_ERR_FATAL;
+    }
+}
+
+/* How many bytes have we transferred since the beginning of the migration */
+static uint64_t migration_total_bytes(MigrationState *s)
+{
+    return qemu_ftell(s->to_dst_file) + ram_counters.multifd_bytes;
+}
+
+static void migration_calculate_complete(MigrationState *s)
+{
+    uint64_t bytes = migration_total_bytes(s);
+    int64_t end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    int64_t transfer_time;
+
+    s->total_time = end_time - s->start_time;
+    if (!s->downtime) {
+        /*
+         * It's still not set, so we are precopy migration.  For
+         * postcopy, downtime is calculated during postcopy_start().
+         */
+        s->downtime = end_time - s->downtime_start;
+    }
+
+    transfer_time = s->total_time - s->setup_time;
+    if (transfer_time) {
+        s->mbps = ((double) bytes * 8.0) / transfer_time / 1000;
+    }
+}
+
+static void update_iteration_initial_status(MigrationState *s)
+{
+    /*
+     * Update these three fields at the same time to avoid mismatch info lead
+     * wrong speed calculation.
+     */
+    s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    s->iteration_initial_bytes = migration_total_bytes(s);
+    s->iteration_initial_pages = ram_get_total_transferred_pages();
+}
+
+static void migration_update_counters(MigrationState *s,
+                                      int64_t current_time)
+{
+    uint64_t transferred, transferred_pages, time_spent;
+    uint64_t current_bytes; /* bytes transferred since the beginning */
+    double bandwidth;
+
+    if (current_time < s->iteration_start_time + BUFFER_DELAY) {
+        return;
+    }
+
+    current_bytes = migration_total_bytes(s);
+    transferred = current_bytes - s->iteration_initial_bytes;
+    time_spent = current_time - s->iteration_start_time;
+    bandwidth = (double)transferred / time_spent;
+    s->threshold_size = bandwidth * s->parameters.downtime_limit;
+
+    s->mbps = (((double) transferred * 8.0) /
+               ((double) time_spent / 1000.0)) / 1000.0 / 1000.0;
+
+    transferred_pages = ram_get_total_transferred_pages() -
+                            s->iteration_initial_pages;
+    s->pages_per_second = (double) transferred_pages /
+                             (((double) time_spent / 1000.0));
+
+    /*
+     * 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 > 10000) {
+        s->expected_downtime = ram_counters.remaining / bandwidth;
+    }
+
+    qemu_file_reset_rate_limit(s->to_dst_file);
+
+    update_iteration_initial_status(s);
+
+    trace_migrate_transferred(transferred, time_spent,
+                              bandwidth, s->threshold_size);
+}
+
+/* Migration thread iteration status */
+typedef enum {
+    MIG_ITERATE_RESUME,         /* Resume current iteration */
+    MIG_ITERATE_SKIP,           /* Skip current iteration */
+    MIG_ITERATE_BREAK,          /* Break the loop */
+} MigIterateState;
+
+/*
+ * Return true if continue to the next iteration directly, false
+ * otherwise.
+ */
+static MigIterateState migration_iteration_run(MigrationState *s)
+{
+    uint64_t pending_size, pend_pre, pend_compat, pend_post;
+    bool in_postcopy = s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE;
+
+    qemu_savevm_state_pending(s->to_dst_file, s->threshold_size, &pend_pre,
+                              &pend_compat, &pend_post);
+    pending_size = pend_pre + pend_compat + pend_post;
+
+    trace_migrate_pending(pending_size, s->threshold_size,
+                          pend_pre, pend_compat, pend_post);
+
+    if (pending_size && pending_size >= s->threshold_size) {
+        /* Still a significant amount to transfer */
+        if (!in_postcopy && pend_pre <= s->threshold_size &&
+            qatomic_read(&s->start_postcopy)) {
+            if (postcopy_start(s)) {
+                error_report("%s: postcopy failed to start", __func__);
+            }
+            return MIG_ITERATE_SKIP;
+        }
+        /* Just another iteration step */
+        qemu_savevm_state_iterate(s->to_dst_file, in_postcopy);
+    } else {
+        trace_migration_thread_low_pending(pending_size);
+        migration_completion(s);
+        return MIG_ITERATE_BREAK;
+    }
+
+    return MIG_ITERATE_RESUME;
+}
+
+static void migration_iteration_finish(MigrationState *s)
+{
+    /* If we enabled cpu throttling for auto-converge, turn it off. */
+    cpu_throttle_stop();
+
+    qemu_mutex_lock_iothread();
+    switch (s->state) {
+    case MIGRATION_STATUS_COMPLETED:
+        migration_calculate_complete(s);
+        runstate_set(RUN_STATE_POSTMIGRATE);
+        break;
+
+    case MIGRATION_STATUS_ACTIVE:
+        /*
+         * We should really assert here, but since it's during
+         * migration, let's try to reduce the usage of assertions.
+         */
+        if (!migrate_colo_enabled()) {
+            error_report("%s: critical error: calling COLO code without "
+                         "COLO enabled", __func__);
+        }
+        migrate_start_colo_process(s);
+        /*
+         * Fixme: we will run VM in COLO no matter its old running state.
+         * After exited COLO, we will keep running.
+         */
+        s->vm_was_running = true;
+        /* Fallthrough */
+    case MIGRATION_STATUS_FAILED:
+    case MIGRATION_STATUS_CANCELLED:
+    case MIGRATION_STATUS_CANCELLING:
+        if (s->vm_was_running) {
+            if (!runstate_check(RUN_STATE_SHUTDOWN)) {
+                vm_start();
+            }
+        } else {
+            if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
+                runstate_set(RUN_STATE_POSTMIGRATE);
+            }
+        }
+        break;
+
+    default:
+        /* Should not reach here, but if so, forgive the VM. */
+        error_report("%s: Unknown ending state %d", __func__, s->state);
+        break;
+    }
+    migrate_fd_cleanup_schedule(s);
+    qemu_mutex_unlock_iothread();
+}
+
+static void bg_migration_iteration_finish(MigrationState *s)
+{
+    qemu_mutex_lock_iothread();
+    switch (s->state) {
+    case MIGRATION_STATUS_COMPLETED:
+        migration_calculate_complete(s);
+        break;
+
+    case MIGRATION_STATUS_ACTIVE:
+    case MIGRATION_STATUS_FAILED:
+    case MIGRATION_STATUS_CANCELLED:
+    case MIGRATION_STATUS_CANCELLING:
+        break;
+
+    default:
+        /* Should not reach here, but if so, forgive the VM. */
+        error_report("%s: Unknown ending state %d", __func__, s->state);
+        break;
+    }
+
+    migrate_fd_cleanup_schedule(s);
+    qemu_mutex_unlock_iothread();
+}
+
+/*
+ * Return true if continue to the next iteration directly, false
+ * otherwise.
+ */
+static MigIterateState bg_migration_iteration_run(MigrationState *s)
+{
+    int res;
+
+    res = qemu_savevm_state_iterate(s->to_dst_file, false);
+    if (res > 0) {
+        bg_migration_completion(s);
+        return MIG_ITERATE_BREAK;
+    }
+
+    return MIG_ITERATE_RESUME;
+}
+
+void migration_make_urgent_request(void)
+{
+    qemu_sem_post(&migrate_get_current()->rate_limit_sem);
+}
+
+void migration_consume_urgent_request(void)
+{
+    qemu_sem_wait(&migrate_get_current()->rate_limit_sem);
+}
+
+/* Returns true if the rate limiting was broken by an urgent request */
+bool migration_rate_limit(void)
+{
+    int64_t now = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    MigrationState *s = migrate_get_current();
+
+    bool urgent = false;
+    migration_update_counters(s, now);
+    if (qemu_file_rate_limit(s->to_dst_file)) {
+
+        if (qemu_file_get_error(s->to_dst_file)) {
+            return false;
+        }
+        /*
+         * Wait for a delay to do rate limiting OR
+         * something urgent to post the semaphore.
+         */
+        int ms = s->iteration_start_time + BUFFER_DELAY - now;
+        trace_migration_rate_limit_pre(ms);
+        if (qemu_sem_timedwait(&s->rate_limit_sem, ms) == 0) {
+            /*
+             * We were woken by one or more urgent things but
+             * the timedwait will have consumed one of them.
+             * The service routine for the urgent wake will dec
+             * the semaphore itself for each item it consumes,
+             * so add this one we just eat back.
+             */
+            qemu_sem_post(&s->rate_limit_sem);
+            urgent = true;
+        }
+        trace_migration_rate_limit_post(urgent);
+    }
+    return urgent;
+}
+
+/*
+ * if failover devices are present, wait they are completely
+ * unplugged
+ */
+
+static void qemu_savevm_wait_unplug(MigrationState *s, int old_state,
+                                    int new_state)
+{
+    if (qemu_savevm_state_guest_unplug_pending()) {
+        migrate_set_state(&s->state, old_state, MIGRATION_STATUS_WAIT_UNPLUG);
+
+        while (s->state == MIGRATION_STATUS_WAIT_UNPLUG &&
+               qemu_savevm_state_guest_unplug_pending()) {
+            qemu_sem_timedwait(&s->wait_unplug_sem, 250);
+        }
+        if (s->state != MIGRATION_STATUS_WAIT_UNPLUG) {
+            int timeout = 120; /* 30 seconds */
+            /*
+             * migration has been canceled
+             * but as we have started an unplug we must wait the end
+             * to be able to plug back the card
+             */
+            while (timeout-- && qemu_savevm_state_guest_unplug_pending()) {
+                qemu_sem_timedwait(&s->wait_unplug_sem, 250);
+            }
+            if (qemu_savevm_state_guest_unplug_pending()) {
+                warn_report("migration: partially unplugged device on "
+                            "failure");
+            }
+        }
+
+        migrate_set_state(&s->state, MIGRATION_STATUS_WAIT_UNPLUG, new_state);
+    } else {
+        migrate_set_state(&s->state, old_state, new_state);
+    }
+}
+
+/*
+ * 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;
+    int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+    MigThrError thr_error;
+    bool urgent = false;
+
+    rcu_register_thread();
+
+    object_ref(OBJECT(s));
+    update_iteration_initial_status(s);
+
+    qemu_savevm_state_header(s->to_dst_file);
+
+    /*
+     * If we opened the return path, we need to make sure dst has it
+     * opened as well.
+     */
+    if (s->rp_state.rp_thread_created) {
+        /* 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()) {
+        /*
+         * 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);
+    }
+
+    if (migrate_colo_enabled()) {
+        /* Notify migration destination that we enable COLO */
+        qemu_savevm_send_colo_enable(s->to_dst_file);
+    }
+
+    qemu_savevm_state_setup(s->to_dst_file);
+
+    qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
+                               MIGRATION_STATUS_ACTIVE);
+
+    s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
+
+    trace_migration_thread_setup_complete();
+
+    while (migration_is_active(s)) {
+        if (urgent || !qemu_file_rate_limit(s->to_dst_file)) {
+            MigIterateState iter_state = migration_iteration_run(s);
+            if (iter_state == MIG_ITERATE_SKIP) {
+                continue;
+            } else if (iter_state == MIG_ITERATE_BREAK) {
+                break;
+            }
+        }
+
+        /*
+         * Try to detect any kind of failures, and see whether we
+         * should stop the migration now.
+         */
+        thr_error = migration_detect_error(s);
+        if (thr_error == MIG_THR_ERR_FATAL) {
+            /* Stop migration */
+            break;
+        } else if (thr_error == MIG_THR_ERR_RECOVERED) {
+            /*
+             * Just recovered from a e.g. network failure, reset all
+             * the local variables. This is important to avoid
+             * breaking transferred_bytes and bandwidth calculation
+             */
+            update_iteration_initial_status(s);
+        }
+
+        urgent = migration_rate_limit();
+    }
+
+    trace_migration_thread_after_loop();
+    migration_iteration_finish(s);
+    object_unref(OBJECT(s));
+    rcu_unregister_thread();
+    return NULL;
+}
+
+static void bg_migration_vm_start_bh(void *opaque)
+{
+    MigrationState *s = opaque;
+
+    qemu_bh_delete(s->vm_start_bh);
+    s->vm_start_bh = NULL;
+
+    vm_start();
+    s->downtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - s->downtime_start;
+}
+
+/**
+ * Background snapshot thread, based on live migration code.
+ * This is an alternative implementation of live migration mechanism
+ * introduced specifically to support background snapshots.
+ *
+ * It takes advantage of userfault_fd write protection mechanism introduced
+ * in v5.7 kernel. Compared to existing dirty page logging migration much
+ * lesser stream traffic is produced resulting in smaller snapshot images,
+ * simply cause of no page duplicates can get into the stream.
+ *
+ * Another key point is that generated vmstate stream reflects machine state
+ * 'frozen' at the beginning of snapshot creation compared to dirty page logging
+ * mechanism, which effectively results in that saved snapshot is the state of VM
+ * at the end of the process.
+ */
+static void *bg_migration_thread(void *opaque)
+{
+    MigrationState *s = opaque;
+    int64_t setup_start;
+    MigThrError thr_error;
+    QEMUFile *fb;
+    bool early_fail = true;
+
+    rcu_register_thread();
+    object_ref(OBJECT(s));
+
+    qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX);
+
+    setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+    /*
+     * We want to save vmstate for the moment when migration has been
+     * initiated but also we want to save RAM content while VM is running.
+     * The RAM content should appear first in the vmstate. So, we first
+     * stash the non-RAM part of the vmstate to the temporary buffer,
+     * then write RAM part of the vmstate to the migration stream
+     * with vCPUs running and, finally, write stashed non-RAM part of
+     * the vmstate from the buffer to the migration stream.
+     */
+    s->bioc = qio_channel_buffer_new(512 * 1024);
+    qio_channel_set_name(QIO_CHANNEL(s->bioc), "vmstate-buffer");
+    fb = qemu_fopen_channel_output(QIO_CHANNEL(s->bioc));
+    object_unref(OBJECT(s->bioc));
+
+    update_iteration_initial_status(s);
+
+    /*
+     * Prepare for tracking memory writes with UFFD-WP - populate
+     * RAM pages before protecting.
+     */
+#ifdef __linux__
+    ram_write_tracking_prepare();
+#endif
+
+    qemu_savevm_state_header(s->to_dst_file);
+    qemu_savevm_state_setup(s->to_dst_file);
+
+    qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
+                               MIGRATION_STATUS_ACTIVE);
+
+    s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
+
+    trace_migration_thread_setup_complete();
+    s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+
+    qemu_mutex_lock_iothread();
+
+    /*
+     * If VM is currently in suspended state, then, to make a valid runstate
+     * transition in vm_stop_force_state() we need to wakeup it up.
+     */
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
+    s->vm_was_running = runstate_is_running();
+
+    if (global_state_store()) {
+        goto fail;
+    }
+    /* Forcibly stop VM before saving state of vCPUs and devices */
+    if (vm_stop_force_state(RUN_STATE_PAUSED)) {
+        goto fail;
+    }
+    /*
+     * Put vCPUs in sync with shadow context structures, then
+     * save their state to channel-buffer along with devices.
+     */
+    cpu_synchronize_all_states();
+    if (qemu_savevm_state_complete_precopy_non_iterable(fb, false, false)) {
+        goto fail;
+    }
+    /*
+     * Since we are going to get non-iterable state data directly
+     * from s->bioc->data, explicit flush is needed here.
+     */
+    qemu_fflush(fb);
+
+    /* Now initialize UFFD context and start tracking RAM writes */
+    if (ram_write_tracking_start()) {
+        goto fail;
+    }
+    early_fail = false;
+
+    /*
+     * Start VM from BH handler to avoid write-fault lock here.
+     * UFFD-WP protection for the whole RAM is already enabled so
+     * calling VM state change notifiers from vm_start() would initiate
+     * writes to virtio VQs memory which is in write-protected region.
+     */
+    s->vm_start_bh = qemu_bh_new(bg_migration_vm_start_bh, s);
+    qemu_bh_schedule(s->vm_start_bh);
+
+    qemu_mutex_unlock_iothread();
+
+    while (migration_is_active(s)) {
+        MigIterateState iter_state = bg_migration_iteration_run(s);
+        if (iter_state == MIG_ITERATE_SKIP) {
+            continue;
+        } else if (iter_state == MIG_ITERATE_BREAK) {
+            break;
+        }
+
+        /*
+         * Try to detect any kind of failures, and see whether we
+         * should stop the migration now.
+         */
+        thr_error = migration_detect_error(s);
+        if (thr_error == MIG_THR_ERR_FATAL) {
+            /* Stop migration */
+            break;
+        }
+
+        migration_update_counters(s, qemu_clock_get_ms(QEMU_CLOCK_REALTIME));
+    }
+
+    trace_migration_thread_after_loop();
+
+fail:
+    if (early_fail) {
+        migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
+                MIGRATION_STATUS_FAILED);
+        qemu_mutex_unlock_iothread();
+    }
+
+    bg_migration_iteration_finish(s);
+
+    qemu_fclose(fb);
+    object_unref(OBJECT(s));
+    rcu_unregister_thread();
+
+    return NULL;
+}
+
+void migrate_fd_connect(MigrationState *s, Error *error_in)
+{
+    Error *local_err = NULL;
+    int64_t rate_limit;
+    bool resume = s->state == MIGRATION_STATUS_POSTCOPY_PAUSED;
+
+    /*
+     * If there's a previous error, free it and prepare for another one.
+     * Meanwhile if migration completes successfully, there won't have an error
+     * dumped when calling migrate_fd_cleanup().
+     */
+    migrate_error_free(s);
+
+    s->expected_downtime = s->parameters.downtime_limit;
+    if (resume) {
+        assert(s->cleanup_bh);
+    } else {
+        assert(!s->cleanup_bh);
+        s->cleanup_bh = qemu_bh_new(migrate_fd_cleanup_bh, s);
+    }
+    if (error_in) {
+        migrate_fd_error(s, error_in);
+        if (resume) {
+            /*
+             * Don't do cleanup for resume if channel is invalid, but only dump
+             * the error.  We wait for another channel connect from the user.
+             * The error_report still gives HMP user a hint on what failed.
+             * It's normally done in migrate_fd_cleanup(), but call it here
+             * explicitly.
+             */
+            error_report_err(error_copy(s->error));
+        } else {
+            migrate_fd_cleanup(s);
+        }
+        return;
+    }
+
+    if (resume) {
+        /* This is a resumed migration */
+        rate_limit = s->parameters.max_postcopy_bandwidth /
+            XFER_LIMIT_RATIO;
+    } else {
+        /* This is a fresh new migration */
+        rate_limit = s->parameters.max_bandwidth / XFER_LIMIT_RATIO;
+
+        /* Notify before starting migration thread */
+        notifier_list_notify(&migration_state_notifiers, s);
+    }
+
+    qemu_file_set_rate_limit(s->to_dst_file, rate_limit);
+    qemu_file_set_blocking(s->to_dst_file, true);
+
+    /*
+     * Open the return path. For postcopy, it is used exclusively. For
+     * precopy, only if user specified "return-path" capability would
+     * QEMU uses the return path.
+     */
+    if (migrate_postcopy_ram() || migrate_use_return_path()) {
+        if (open_return_path_on_source(s, !resume)) {
+            error_report("Unable to open return-path for postcopy");
+            migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
+            migrate_fd_cleanup(s);
+            return;
+        }
+    }
+
+    if (resume) {
+        /* Wakeup the main migration thread to do the recovery */
+        migrate_set_state(&s->state, MIGRATION_STATUS_POSTCOPY_PAUSED,
+                          MIGRATION_STATUS_POSTCOPY_RECOVER);
+        qemu_sem_post(&s->postcopy_pause_sem);
+        return;
+    }
+
+    if (multifd_save_setup(&local_err) != 0) {
+        error_report_err(local_err);
+        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                          MIGRATION_STATUS_FAILED);
+        migrate_fd_cleanup(s);
+        return;
+    }
+
+    if (migrate_background_snapshot()) {
+        qemu_thread_create(&s->thread, "bg_snapshot",
+                bg_migration_thread, s, QEMU_THREAD_JOINABLE);
+    } else {
+        qemu_thread_create(&s->thread, "live_migration",
+                migration_thread, s, QEMU_THREAD_JOINABLE);
+    }
+    s->migration_thread_running = true;
+}
+
+void migration_global_dump(Monitor *mon)
+{
+    MigrationState *ms = migrate_get_current();
+
+    monitor_printf(mon, "globals:\n");
+    monitor_printf(mon, "store-global-state: %s\n",
+                   ms->store_global_state ? "on" : "off");
+    monitor_printf(mon, "only-migratable: %s\n",
+                   only_migratable ? "on" : "off");
+    monitor_printf(mon, "send-configuration: %s\n",
+                   ms->send_configuration ? "on" : "off");
+    monitor_printf(mon, "send-section-footer: %s\n",
+                   ms->send_section_footer ? "on" : "off");
+    monitor_printf(mon, "decompress-error-check: %s\n",
+                   ms->decompress_error_check ? "on" : "off");
+    monitor_printf(mon, "clear-bitmap-shift: %u\n",
+                   ms->clear_bitmap_shift);
+}
+
+#define DEFINE_PROP_MIG_CAP(name, x)             \
+    DEFINE_PROP_BOOL(name, MigrationState, enabled_capabilities[x], false)
+
+static Property migration_properties[] = {
+    DEFINE_PROP_BOOL("store-global-state", MigrationState,
+                     store_global_state, true),
+    DEFINE_PROP_BOOL("send-configuration", MigrationState,
+                     send_configuration, true),
+    DEFINE_PROP_BOOL("send-section-footer", MigrationState,
+                     send_section_footer, true),
+    DEFINE_PROP_BOOL("decompress-error-check", MigrationState,
+                      decompress_error_check, true),
+    DEFINE_PROP_UINT8("x-clear-bitmap-shift", MigrationState,
+                      clear_bitmap_shift, CLEAR_BITMAP_SHIFT_DEFAULT),
+
+    /* Migration parameters */
+    DEFINE_PROP_UINT8("x-compress-level", MigrationState,
+                      parameters.compress_level,
+                      DEFAULT_MIGRATE_COMPRESS_LEVEL),
+    DEFINE_PROP_UINT8("x-compress-threads", MigrationState,
+                      parameters.compress_threads,
+                      DEFAULT_MIGRATE_COMPRESS_THREAD_COUNT),
+    DEFINE_PROP_BOOL("x-compress-wait-thread", MigrationState,
+                      parameters.compress_wait_thread, true),
+    DEFINE_PROP_UINT8("x-decompress-threads", MigrationState,
+                      parameters.decompress_threads,
+                      DEFAULT_MIGRATE_DECOMPRESS_THREAD_COUNT),
+    DEFINE_PROP_UINT8("x-throttle-trigger-threshold", MigrationState,
+                      parameters.throttle_trigger_threshold,
+                      DEFAULT_MIGRATE_THROTTLE_TRIGGER_THRESHOLD),
+    DEFINE_PROP_UINT8("x-cpu-throttle-initial", MigrationState,
+                      parameters.cpu_throttle_initial,
+                      DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL),
+    DEFINE_PROP_UINT8("x-cpu-throttle-increment", MigrationState,
+                      parameters.cpu_throttle_increment,
+                      DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT),
+    DEFINE_PROP_BOOL("x-cpu-throttle-tailslow", MigrationState,
+                      parameters.cpu_throttle_tailslow, false),
+    DEFINE_PROP_SIZE("x-max-bandwidth", MigrationState,
+                      parameters.max_bandwidth, MAX_THROTTLE),
+    DEFINE_PROP_UINT64("x-downtime-limit", MigrationState,
+                      parameters.downtime_limit,
+                      DEFAULT_MIGRATE_SET_DOWNTIME),
+    DEFINE_PROP_UINT32("x-checkpoint-delay", MigrationState,
+                      parameters.x_checkpoint_delay,
+                      DEFAULT_MIGRATE_X_CHECKPOINT_DELAY),
+    DEFINE_PROP_UINT8("multifd-channels", MigrationState,
+                      parameters.multifd_channels,
+                      DEFAULT_MIGRATE_MULTIFD_CHANNELS),
+    DEFINE_PROP_MULTIFD_COMPRESSION("multifd-compression", MigrationState,
+                      parameters.multifd_compression,
+                      DEFAULT_MIGRATE_MULTIFD_COMPRESSION),
+    DEFINE_PROP_UINT8("multifd-zlib-level", MigrationState,
+                      parameters.multifd_zlib_level,
+                      DEFAULT_MIGRATE_MULTIFD_ZLIB_LEVEL),
+    DEFINE_PROP_UINT8("multifd-zstd-level", MigrationState,
+                      parameters.multifd_zstd_level,
+                      DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL),
+    DEFINE_PROP_SIZE("xbzrle-cache-size", MigrationState,
+                      parameters.xbzrle_cache_size,
+                      DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
+    DEFINE_PROP_SIZE("max-postcopy-bandwidth", MigrationState,
+                      parameters.max_postcopy_bandwidth,
+                      DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH),
+    DEFINE_PROP_UINT8("max-cpu-throttle", MigrationState,
+                      parameters.max_cpu_throttle,
+                      DEFAULT_MIGRATE_MAX_CPU_THROTTLE),
+    DEFINE_PROP_SIZE("announce-initial", MigrationState,
+                      parameters.announce_initial,
+                      DEFAULT_MIGRATE_ANNOUNCE_INITIAL),
+    DEFINE_PROP_SIZE("announce-max", MigrationState,
+                      parameters.announce_max,
+                      DEFAULT_MIGRATE_ANNOUNCE_MAX),
+    DEFINE_PROP_SIZE("announce-rounds", MigrationState,
+                      parameters.announce_rounds,
+                      DEFAULT_MIGRATE_ANNOUNCE_ROUNDS),
+    DEFINE_PROP_SIZE("announce-step", MigrationState,
+                      parameters.announce_step,
+                      DEFAULT_MIGRATE_ANNOUNCE_STEP),
+
+    /* Migration capabilities */
+    DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
+    DEFINE_PROP_MIG_CAP("x-rdma-pin-all", MIGRATION_CAPABILITY_RDMA_PIN_ALL),
+    DEFINE_PROP_MIG_CAP("x-auto-converge", MIGRATION_CAPABILITY_AUTO_CONVERGE),
+    DEFINE_PROP_MIG_CAP("x-zero-blocks", MIGRATION_CAPABILITY_ZERO_BLOCKS),
+    DEFINE_PROP_MIG_CAP("x-compress", MIGRATION_CAPABILITY_COMPRESS),
+    DEFINE_PROP_MIG_CAP("x-events", MIGRATION_CAPABILITY_EVENTS),
+    DEFINE_PROP_MIG_CAP("x-postcopy-ram", MIGRATION_CAPABILITY_POSTCOPY_RAM),
+    DEFINE_PROP_MIG_CAP("x-colo", MIGRATION_CAPABILITY_X_COLO),
+    DEFINE_PROP_MIG_CAP("x-release-ram", MIGRATION_CAPABILITY_RELEASE_RAM),
+    DEFINE_PROP_MIG_CAP("x-block", MIGRATION_CAPABILITY_BLOCK),
+    DEFINE_PROP_MIG_CAP("x-return-path", MIGRATION_CAPABILITY_RETURN_PATH),
+    DEFINE_PROP_MIG_CAP("x-multifd", MIGRATION_CAPABILITY_MULTIFD),
+    DEFINE_PROP_MIG_CAP("x-background-snapshot",
+            MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT),
+
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void migration_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->user_creatable = false;
+    device_class_set_props(dc, migration_properties);
+}
+
+static void migration_instance_finalize(Object *obj)
+{
+    MigrationState *ms = MIGRATION_OBJ(obj);
+    MigrationParameters *params = &ms->parameters;
+
+    qemu_mutex_destroy(&ms->error_mutex);
+    qemu_mutex_destroy(&ms->qemu_file_lock);
+    g_free(params->tls_hostname);
+    g_free(params->tls_creds);
+    qemu_sem_destroy(&ms->wait_unplug_sem);
+    qemu_sem_destroy(&ms->rate_limit_sem);
+    qemu_sem_destroy(&ms->pause_sem);
+    qemu_sem_destroy(&ms->postcopy_pause_sem);
+    qemu_sem_destroy(&ms->postcopy_pause_rp_sem);
+    qemu_sem_destroy(&ms->rp_state.rp_sem);
+    error_free(ms->error);
+}
+
+static void migration_instance_init(Object *obj)
+{
+    MigrationState *ms = MIGRATION_OBJ(obj);
+    MigrationParameters *params = &ms->parameters;
+
+    ms->state = MIGRATION_STATUS_NONE;
+    ms->mbps = -1;
+    ms->pages_per_second = -1;
+    qemu_sem_init(&ms->pause_sem, 0);
+    qemu_mutex_init(&ms->error_mutex);
+
+    params->tls_hostname = g_strdup("");
+    params->tls_creds = g_strdup("");
+
+    /* Set has_* up only for parameter checks */
+    params->has_compress_level = true;
+    params->has_compress_threads = true;
+    params->has_decompress_threads = true;
+    params->has_throttle_trigger_threshold = true;
+    params->has_cpu_throttle_initial = true;
+    params->has_cpu_throttle_increment = true;
+    params->has_cpu_throttle_tailslow = true;
+    params->has_max_bandwidth = true;
+    params->has_downtime_limit = true;
+    params->has_x_checkpoint_delay = true;
+    params->has_block_incremental = true;
+    params->has_multifd_channels = true;
+    params->has_multifd_compression = true;
+    params->has_multifd_zlib_level = true;
+    params->has_multifd_zstd_level = true;
+    params->has_xbzrle_cache_size = true;
+    params->has_max_postcopy_bandwidth = true;
+    params->has_max_cpu_throttle = true;
+    params->has_announce_initial = true;
+    params->has_announce_max = true;
+    params->has_announce_rounds = true;
+    params->has_announce_step = true;
+
+    qemu_sem_init(&ms->postcopy_pause_sem, 0);
+    qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);
+    qemu_sem_init(&ms->rp_state.rp_sem, 0);
+    qemu_sem_init(&ms->rate_limit_sem, 0);
+    qemu_sem_init(&ms->wait_unplug_sem, 0);
+    qemu_mutex_init(&ms->qemu_file_lock);
+}
+
+/*
+ * Return true if check pass, false otherwise. Error will be put
+ * inside errp if provided.
+ */
+static bool migration_object_check(MigrationState *ms, Error **errp)
+{
+    MigrationCapabilityStatusList *head = NULL;
+    /* Assuming all off */
+    bool cap_list[MIGRATION_CAPABILITY__MAX] = { 0 }, ret;
+    int i;
+
+    if (!migrate_params_check(&ms->parameters, errp)) {
+        return false;
+    }
+
+    for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
+        if (ms->enabled_capabilities[i]) {
+            QAPI_LIST_PREPEND(head, migrate_cap_add(i, true));
+        }
+    }
+
+    ret = migrate_caps_check(cap_list, head, errp);
+
+    /* It works with head == NULL */
+    qapi_free_MigrationCapabilityStatusList(head);
+
+    return ret;
+}
+
+static const TypeInfo migration_type = {
+    .name = TYPE_MIGRATION,
+    /*
+     * NOTE: TYPE_MIGRATION is not really a device, as the object is
+     * not created using qdev_new(), it is not attached to the qdev
+     * device tree, and it is never realized.
+     *
+     * TODO: Make this TYPE_OBJECT once QOM provides something like
+     * TYPE_DEVICE's "-global" properties.
+     */
+    .parent = TYPE_DEVICE,
+    .class_init = migration_class_init,
+    .class_size = sizeof(MigrationClass),
+    .instance_size = sizeof(MigrationState),
+    .instance_init = migration_instance_init,
+    .instance_finalize = migration_instance_finalize,
+};
+
+static void register_migration_types(void)
+{
+    type_register_static(&migration_type);
+}
+
+type_init(register_migration_types);