multifd: Split multifd code into its own file

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 899 insertions, 0 deletions

diff --git a/migration/multifd.c b/migration/multifd.c
new file mode 100644
index 0000000000..b3e8ae9bcc
--- /dev/null
+++ b/migration/multifd.c
@@ -0,0 +1,899 @@
+/*
+ * Multifd common code
+ *
+ * Copyright (c) 2019-2020 Red Hat Inc
+ *
+ * Authors:
+ *  Juan Quintela <quintela@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/rcu.h"
+#include "exec/target_page.h"
+#include "sysemu/sysemu.h"
+#include "exec/ramblock.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+#include "ram.h"
+#include "migration.h"
+#include "socket.h"
+#include "qemu-file.h"
+#include "trace.h"
+#include "multifd.h"
+
+/* Multiple fd's */
+
+#define MULTIFD_MAGIC 0x11223344U
+#define MULTIFD_VERSION 1
+
+typedef struct {
+    uint32_t magic;
+    uint32_t version;
+    unsigned char uuid[16]; /* QemuUUID */
+    uint8_t id;
+    uint8_t unused1[7];     /* Reserved for future use */
+    uint64_t unused2[4];    /* Reserved for future use */
+} __attribute__((packed)) MultiFDInit_t;
+
+static int multifd_send_initial_packet(MultiFDSendParams *p, Error **errp)
+{
+    MultiFDInit_t msg = {};
+    int ret;
+
+    msg.magic = cpu_to_be32(MULTIFD_MAGIC);
+    msg.version = cpu_to_be32(MULTIFD_VERSION);
+    msg.id = p->id;
+    memcpy(msg.uuid, &qemu_uuid.data, sizeof(msg.uuid));
+
+    ret = qio_channel_write_all(p->c, (char *)&msg, sizeof(msg), errp);
+    if (ret != 0) {
+        return -1;
+    }
+    return 0;
+}
+
+static int multifd_recv_initial_packet(QIOChannel *c, Error **errp)
+{
+    MultiFDInit_t msg;
+    int ret;
+
+    ret = qio_channel_read_all(c, (char *)&msg, sizeof(msg), errp);
+    if (ret != 0) {
+        return -1;
+    }
+
+    msg.magic = be32_to_cpu(msg.magic);
+    msg.version = be32_to_cpu(msg.version);
+
+    if (msg.magic != MULTIFD_MAGIC) {
+        error_setg(errp, "multifd: received packet magic %x "
+                   "expected %x", msg.magic, MULTIFD_MAGIC);
+        return -1;
+    }
+
+    if (msg.version != MULTIFD_VERSION) {
+        error_setg(errp, "multifd: received packet version %d "
+                   "expected %d", msg.version, MULTIFD_VERSION);
+        return -1;
+    }
+
+    if (memcmp(msg.uuid, &qemu_uuid, sizeof(qemu_uuid))) {
+        char *uuid = qemu_uuid_unparse_strdup(&qemu_uuid);
+        char *msg_uuid = qemu_uuid_unparse_strdup((const QemuUUID *)msg.uuid);
+
+        error_setg(errp, "multifd: received uuid '%s' and expected "
+                   "uuid '%s' for channel %hhd", msg_uuid, uuid, msg.id);
+        g_free(uuid);
+        g_free(msg_uuid);
+        return -1;
+    }
+
+    if (msg.id > migrate_multifd_channels()) {
+        error_setg(errp, "multifd: received channel version %d "
+                   "expected %d", msg.version, MULTIFD_VERSION);
+        return -1;
+    }
+
+    return msg.id;
+}
+
+static MultiFDPages_t *multifd_pages_init(size_t size)
+{
+    MultiFDPages_t *pages = g_new0(MultiFDPages_t, 1);
+
+    pages->allocated = size;
+    pages->iov = g_new0(struct iovec, size);
+    pages->offset = g_new0(ram_addr_t, size);
+
+    return pages;
+}
+
+static void multifd_pages_clear(MultiFDPages_t *pages)
+{
+    pages->used = 0;
+    pages->allocated = 0;
+    pages->packet_num = 0;
+    pages->block = NULL;
+    g_free(pages->iov);
+    pages->iov = NULL;
+    g_free(pages->offset);
+    pages->offset = NULL;
+    g_free(pages);
+}
+
+static void multifd_send_fill_packet(MultiFDSendParams *p)
+{
+    MultiFDPacket_t *packet = p->packet;
+    int i;
+
+    packet->flags = cpu_to_be32(p->flags);
+    packet->pages_alloc = cpu_to_be32(p->pages->allocated);
+    packet->pages_used = cpu_to_be32(p->pages->used);
+    packet->next_packet_size = cpu_to_be32(p->next_packet_size);
+    packet->packet_num = cpu_to_be64(p->packet_num);
+
+    if (p->pages->block) {
+        strncpy(packet->ramblock, p->pages->block->idstr, 256);
+    }
+
+    for (i = 0; i < p->pages->used; i++) {
+        /* there are architectures where ram_addr_t is 32 bit */
+        uint64_t temp = p->pages->offset[i];
+
+        packet->offset[i] = cpu_to_be64(temp);
+    }
+}
+
+static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
+{
+    MultiFDPacket_t *packet = p->packet;
+    uint32_t pages_max = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    RAMBlock *block;
+    int i;
+
+    packet->magic = be32_to_cpu(packet->magic);
+    if (packet->magic != MULTIFD_MAGIC) {
+        error_setg(errp, "multifd: received packet "
+                   "magic %x and expected magic %x",
+                   packet->magic, MULTIFD_MAGIC);
+        return -1;
+    }
+
+    packet->version = be32_to_cpu(packet->version);
+    if (packet->version != MULTIFD_VERSION) {
+        error_setg(errp, "multifd: received packet "
+                   "version %d and expected version %d",
+                   packet->version, MULTIFD_VERSION);
+        return -1;
+    }
+
+    p->flags = be32_to_cpu(packet->flags);
+
+    packet->pages_alloc = be32_to_cpu(packet->pages_alloc);
+    /*
+     * If we received a packet that is 100 times bigger than expected
+     * just stop migration.  It is a magic number.
+     */
+    if (packet->pages_alloc > pages_max * 100) {
+        error_setg(errp, "multifd: received packet "
+                   "with size %d and expected a maximum size of %d",
+                   packet->pages_alloc, pages_max * 100) ;
+        return -1;
+    }
+    /*
+     * We received a packet that is bigger than expected but inside
+     * reasonable limits (see previous comment).  Just reallocate.
+     */
+    if (packet->pages_alloc > p->pages->allocated) {
+        multifd_pages_clear(p->pages);
+        p->pages = multifd_pages_init(packet->pages_alloc);
+    }
+
+    p->pages->used = be32_to_cpu(packet->pages_used);
+    if (p->pages->used > packet->pages_alloc) {
+        error_setg(errp, "multifd: received packet "
+                   "with %d pages and expected maximum pages are %d",
+                   p->pages->used, packet->pages_alloc) ;
+        return -1;
+    }
+
+    p->next_packet_size = be32_to_cpu(packet->next_packet_size);
+    p->packet_num = be64_to_cpu(packet->packet_num);
+
+    if (p->pages->used == 0) {
+        return 0;
+    }
+
+    /* make sure that ramblock is 0 terminated */
+    packet->ramblock[255] = 0;
+    block = qemu_ram_block_by_name(packet->ramblock);
+    if (!block) {
+        error_setg(errp, "multifd: unknown ram block %s",
+                   packet->ramblock);
+        return -1;
+    }
+
+    for (i = 0; i < p->pages->used; i++) {
+        uint64_t offset = be64_to_cpu(packet->offset[i]);
+
+        if (offset > (block->used_length - qemu_target_page_size())) {
+            error_setg(errp, "multifd: offset too long %" PRIu64
+                       " (max " RAM_ADDR_FMT ")",
+                       offset, block->max_length);
+            return -1;
+        }
+        p->pages->iov[i].iov_base = block->host + offset;
+        p->pages->iov[i].iov_len = qemu_target_page_size();
+    }
+
+    return 0;
+}
+
+struct {
+    MultiFDSendParams *params;
+    /* array of pages to sent */
+    MultiFDPages_t *pages;
+    /* global number of generated multifd packets */
+    uint64_t packet_num;
+    /* send channels ready */
+    QemuSemaphore channels_ready;
+    /*
+     * Have we already run terminate threads.  There is a race when it
+     * happens that we got one error while we are exiting.
+     * We will use atomic operations.  Only valid values are 0 and 1.
+     */
+    int exiting;
+} *multifd_send_state;
+
+/*
+ * How we use multifd_send_state->pages and channel->pages?
+ *
+ * We create a pages for each channel, and a main one.  Each time that
+ * we need to send a batch of pages we interchange the ones between
+ * multifd_send_state and the channel that is sending it.  There are
+ * two reasons for that:
+ *    - to not have to do so many mallocs during migration
+ *    - to make easier to know what to free at the end of migration
+ *
+ * This way we always know who is the owner of each "pages" struct,
+ * and we don't need any locking.  It belongs to the migration thread
+ * or to the channel thread.  Switching is safe because the migration
+ * thread is using the channel mutex when changing it, and the channel
+ * have to had finish with its own, otherwise pending_job can't be
+ * false.
+ */
+
+static int multifd_send_pages(QEMUFile *f)
+{
+    int i;
+    static int next_channel;
+    MultiFDSendParams *p = NULL; /* make happy gcc */
+    MultiFDPages_t *pages = multifd_send_state->pages;
+    uint64_t transferred;
+
+    if (atomic_read(&multifd_send_state->exiting)) {
+        return -1;
+    }
+
+    qemu_sem_wait(&multifd_send_state->channels_ready);
+    for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) {
+        p = &multifd_send_state->params[i];
+
+        qemu_mutex_lock(&p->mutex);
+        if (p->quit) {
+            error_report("%s: channel %d has already quit!", __func__, i);
+            qemu_mutex_unlock(&p->mutex);
+            return -1;
+        }
+        if (!p->pending_job) {
+            p->pending_job++;
+            next_channel = (i + 1) % migrate_multifd_channels();
+            break;
+        }
+        qemu_mutex_unlock(&p->mutex);
+    }
+    assert(!p->pages->used);
+    assert(!p->pages->block);
+
+    p->packet_num = multifd_send_state->packet_num++;
+    multifd_send_state->pages = p->pages;
+    p->pages = pages;
+    transferred = ((uint64_t) pages->used) * qemu_target_page_size()
+                + p->packet_len;
+    qemu_file_update_transfer(f, transferred);
+    ram_counters.multifd_bytes += transferred;
+    ram_counters.transferred += transferred;;
+    qemu_mutex_unlock(&p->mutex);
+    qemu_sem_post(&p->sem);
+
+    return 1;
+}
+
+int multifd_queue_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset)
+{
+    MultiFDPages_t *pages = multifd_send_state->pages;
+
+    if (!pages->block) {
+        pages->block = block;
+    }
+
+    if (pages->block == block) {
+        pages->offset[pages->used] = offset;
+        pages->iov[pages->used].iov_base = block->host + offset;
+        pages->iov[pages->used].iov_len = qemu_target_page_size();
+        pages->used++;
+
+        if (pages->used < pages->allocated) {
+            return 1;
+        }
+    }
+
+    if (multifd_send_pages(f) < 0) {
+        return -1;
+    }
+
+    if (pages->block != block) {
+        return  multifd_queue_page(f, block, offset);
+    }
+
+    return 1;
+}
+
+static void multifd_send_terminate_threads(Error *err)
+{
+    int i;
+
+    trace_multifd_send_terminate_threads(err != NULL);
+
+    if (err) {
+        MigrationState *s = migrate_get_current();
+        migrate_set_error(s, err);
+        if (s->state == MIGRATION_STATUS_SETUP ||
+            s->state == MIGRATION_STATUS_PRE_SWITCHOVER ||
+            s->state == MIGRATION_STATUS_DEVICE ||
+            s->state == MIGRATION_STATUS_ACTIVE) {
+            migrate_set_state(&s->state, s->state,
+                              MIGRATION_STATUS_FAILED);
+        }
+    }
+
+    /*
+     * We don't want to exit each threads twice.  Depending on where
+     * we get the error, or if there are two independent errors in two
+     * threads at the same time, we can end calling this function
+     * twice.
+     */
+    if (atomic_xchg(&multifd_send_state->exiting, 1)) {
+        return;
+    }
+
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        qemu_mutex_lock(&p->mutex);
+        p->quit = true;
+        qemu_sem_post(&p->sem);
+        qemu_mutex_unlock(&p->mutex);
+    }
+}
+
+void multifd_save_cleanup(void)
+{
+    int i;
+
+    if (!migrate_use_multifd()) {
+        return;
+    }
+    multifd_send_terminate_threads(NULL);
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        if (p->running) {
+            qemu_thread_join(&p->thread);
+        }
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        socket_send_channel_destroy(p->c);
+        p->c = NULL;
+        qemu_mutex_destroy(&p->mutex);
+        qemu_sem_destroy(&p->sem);
+        qemu_sem_destroy(&p->sem_sync);
+        g_free(p->name);
+        p->name = NULL;
+        multifd_pages_clear(p->pages);
+        p->pages = NULL;
+        p->packet_len = 0;
+        g_free(p->packet);
+        p->packet = NULL;
+    }
+    qemu_sem_destroy(&multifd_send_state->channels_ready);
+    g_free(multifd_send_state->params);
+    multifd_send_state->params = NULL;
+    multifd_pages_clear(multifd_send_state->pages);
+    multifd_send_state->pages = NULL;
+    g_free(multifd_send_state);
+    multifd_send_state = NULL;
+}
+
+void multifd_send_sync_main(QEMUFile *f)
+{
+    int i;
+
+    if (!migrate_use_multifd()) {
+        return;
+    }
+    if (multifd_send_state->pages->used) {
+        if (multifd_send_pages(f) < 0) {
+            error_report("%s: multifd_send_pages fail", __func__);
+            return;
+        }
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        trace_multifd_send_sync_main_signal(p->id);
+
+        qemu_mutex_lock(&p->mutex);
+
+        if (p->quit) {
+            error_report("%s: channel %d has already quit", __func__, i);
+            qemu_mutex_unlock(&p->mutex);
+            return;
+        }
+
+        p->packet_num = multifd_send_state->packet_num++;
+        p->flags |= MULTIFD_FLAG_SYNC;
+        p->pending_job++;
+        qemu_file_update_transfer(f, p->packet_len);
+        ram_counters.multifd_bytes += p->packet_len;
+        ram_counters.transferred += p->packet_len;
+        qemu_mutex_unlock(&p->mutex);
+        qemu_sem_post(&p->sem);
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        trace_multifd_send_sync_main_wait(p->id);
+        qemu_sem_wait(&p->sem_sync);
+    }
+    trace_multifd_send_sync_main(multifd_send_state->packet_num);
+}
+
+static void *multifd_send_thread(void *opaque)
+{
+    MultiFDSendParams *p = opaque;
+    Error *local_err = NULL;
+    int ret = 0;
+    uint32_t flags = 0;
+
+    trace_multifd_send_thread_start(p->id);
+    rcu_register_thread();
+
+    if (multifd_send_initial_packet(p, &local_err) < 0) {
+        ret = -1;
+        goto out;
+    }
+    /* initial packet */
+    p->num_packets = 1;
+
+    while (true) {
+        qemu_sem_wait(&p->sem);
+
+        if (atomic_read(&multifd_send_state->exiting)) {
+            break;
+        }
+        qemu_mutex_lock(&p->mutex);
+
+        if (p->pending_job) {
+            uint32_t used = p->pages->used;
+            uint64_t packet_num = p->packet_num;
+            flags = p->flags;
+
+            p->next_packet_size = used * qemu_target_page_size();
+            multifd_send_fill_packet(p);
+            p->flags = 0;
+            p->num_packets++;
+            p->num_pages += used;
+            p->pages->used = 0;
+            p->pages->block = NULL;
+            qemu_mutex_unlock(&p->mutex);
+
+            trace_multifd_send(p->id, packet_num, used, flags,
+                               p->next_packet_size);
+
+            ret = qio_channel_write_all(p->c, (void *)p->packet,
+                                        p->packet_len, &local_err);
+            if (ret != 0) {
+                break;
+            }
+
+            if (used) {
+                ret = qio_channel_writev_all(p->c, p->pages->iov,
+                                             used, &local_err);
+                if (ret != 0) {
+                    break;
+                }
+            }
+
+            qemu_mutex_lock(&p->mutex);
+            p->pending_job--;
+            qemu_mutex_unlock(&p->mutex);
+
+            if (flags & MULTIFD_FLAG_SYNC) {
+                qemu_sem_post(&p->sem_sync);
+            }
+            qemu_sem_post(&multifd_send_state->channels_ready);
+        } else if (p->quit) {
+            qemu_mutex_unlock(&p->mutex);
+            break;
+        } else {
+            qemu_mutex_unlock(&p->mutex);
+            /* sometimes there are spurious wakeups */
+        }
+    }
+
+out:
+    if (local_err) {
+        trace_multifd_send_error(p->id);
+        multifd_send_terminate_threads(local_err);
+    }
+
+    /*
+     * Error happen, I will exit, but I can't just leave, tell
+     * who pay attention to me.
+     */
+    if (ret != 0) {
+        qemu_sem_post(&p->sem_sync);
+        qemu_sem_post(&multifd_send_state->channels_ready);
+    }
+
+    qemu_mutex_lock(&p->mutex);
+    p->running = false;
+    qemu_mutex_unlock(&p->mutex);
+
+    rcu_unregister_thread();
+    trace_multifd_send_thread_end(p->id, p->num_packets, p->num_pages);
+
+    return NULL;
+}
+
+static void multifd_new_send_channel_async(QIOTask *task, gpointer opaque)
+{
+    MultiFDSendParams *p = opaque;
+    QIOChannel *sioc = QIO_CHANNEL(qio_task_get_source(task));
+    Error *local_err = NULL;
+
+    trace_multifd_new_send_channel_async(p->id);
+    if (qio_task_propagate_error(task, &local_err)) {
+        migrate_set_error(migrate_get_current(), local_err);
+        /* Error happen, we need to tell who pay attention to me */
+        qemu_sem_post(&multifd_send_state->channels_ready);
+        qemu_sem_post(&p->sem_sync);
+        /*
+         * Although multifd_send_thread is not created, but main migration
+         * thread neet to judge whether it is running, so we need to mark
+         * its status.
+         */
+        p->quit = true;
+    } else {
+        p->c = QIO_CHANNEL(sioc);
+        qio_channel_set_delay(p->c, false);
+        p->running = true;
+        qemu_thread_create(&p->thread, p->name, multifd_send_thread, p,
+                           QEMU_THREAD_JOINABLE);
+    }
+}
+
+int multifd_save_setup(Error **errp)
+{
+    int thread_count;
+    uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    uint8_t i;
+
+    if (!migrate_use_multifd()) {
+        return 0;
+    }
+    thread_count = migrate_multifd_channels();
+    multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
+    multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
+    multifd_send_state->pages = multifd_pages_init(page_count);
+    qemu_sem_init(&multifd_send_state->channels_ready, 0);
+    atomic_set(&multifd_send_state->exiting, 0);
+
+    for (i = 0; i < thread_count; i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        qemu_mutex_init(&p->mutex);
+        qemu_sem_init(&p->sem, 0);
+        qemu_sem_init(&p->sem_sync, 0);
+        p->quit = false;
+        p->pending_job = 0;
+        p->id = i;
+        p->pages = multifd_pages_init(page_count);
+        p->packet_len = sizeof(MultiFDPacket_t)
+                      + sizeof(uint64_t) * page_count;
+        p->packet = g_malloc0(p->packet_len);
+        p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
+        p->packet->version = cpu_to_be32(MULTIFD_VERSION);
+        p->name = g_strdup_printf("multifdsend_%d", i);
+        socket_send_channel_create(multifd_new_send_channel_async, p);
+    }
+    return 0;
+}
+
+struct {
+    MultiFDRecvParams *params;
+    /* number of created threads */
+    int count;
+    /* syncs main thread and channels */
+    QemuSemaphore sem_sync;
+    /* global number of generated multifd packets */
+    uint64_t packet_num;
+} *multifd_recv_state;
+
+static void multifd_recv_terminate_threads(Error *err)
+{
+    int i;
+
+    trace_multifd_recv_terminate_threads(err != NULL);
+
+    if (err) {
+        MigrationState *s = migrate_get_current();
+        migrate_set_error(s, err);
+        if (s->state == MIGRATION_STATUS_SETUP ||
+            s->state == MIGRATION_STATUS_ACTIVE) {
+            migrate_set_state(&s->state, s->state,
+                              MIGRATION_STATUS_FAILED);
+        }
+    }
+
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        qemu_mutex_lock(&p->mutex);
+        p->quit = true;
+        /*
+         * We could arrive here for two reasons:
+         *  - normal quit, i.e. everything went fine, just finished
+         *  - error quit: We close the channels so the channel threads
+         *    finish the qio_channel_read_all_eof()
+         */
+        if (p->c) {
+            qio_channel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+        }
+        qemu_mutex_unlock(&p->mutex);
+    }
+}
+
+int multifd_load_cleanup(Error **errp)
+{
+    int i;
+    int ret = 0;
+
+    if (!migrate_use_multifd()) {
+        return 0;
+    }
+    multifd_recv_terminate_threads(NULL);
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        if (p->running) {
+            p->quit = true;
+            /*
+             * multifd_recv_thread may hung at MULTIFD_FLAG_SYNC handle code,
+             * however try to wakeup it without harm in cleanup phase.
+             */
+            qemu_sem_post(&p->sem_sync);
+            qemu_thread_join(&p->thread);
+        }
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        object_unref(OBJECT(p->c));
+        p->c = NULL;
+        qemu_mutex_destroy(&p->mutex);
+        qemu_sem_destroy(&p->sem_sync);
+        g_free(p->name);
+        p->name = NULL;
+        multifd_pages_clear(p->pages);
+        p->pages = NULL;
+        p->packet_len = 0;
+        g_free(p->packet);
+        p->packet = NULL;
+    }
+    qemu_sem_destroy(&multifd_recv_state->sem_sync);
+    g_free(multifd_recv_state->params);
+    multifd_recv_state->params = NULL;
+    g_free(multifd_recv_state);
+    multifd_recv_state = NULL;
+
+    return ret;
+}
+
+void multifd_recv_sync_main(void)
+{
+    int i;
+
+    if (!migrate_use_multifd()) {
+        return;
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        trace_multifd_recv_sync_main_wait(p->id);
+        qemu_sem_wait(&multifd_recv_state->sem_sync);
+    }
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        qemu_mutex_lock(&p->mutex);
+        if (multifd_recv_state->packet_num < p->packet_num) {
+            multifd_recv_state->packet_num = p->packet_num;
+        }
+        qemu_mutex_unlock(&p->mutex);
+        trace_multifd_recv_sync_main_signal(p->id);
+        qemu_sem_post(&p->sem_sync);
+    }
+    trace_multifd_recv_sync_main(multifd_recv_state->packet_num);
+}
+
+static void *multifd_recv_thread(void *opaque)
+{
+    MultiFDRecvParams *p = opaque;
+    Error *local_err = NULL;
+    int ret;
+
+    trace_multifd_recv_thread_start(p->id);
+    rcu_register_thread();
+
+    while (true) {
+        uint32_t used;
+        uint32_t flags;
+
+        if (p->quit) {
+            break;
+        }
+
+        ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
+                                       p->packet_len, &local_err);
+        if (ret == 0) {   /* EOF */
+            break;
+        }
+        if (ret == -1) {   /* Error */
+            break;
+        }
+
+        qemu_mutex_lock(&p->mutex);
+        ret = multifd_recv_unfill_packet(p, &local_err);
+        if (ret) {
+            qemu_mutex_unlock(&p->mutex);
+            break;
+        }
+
+        used = p->pages->used;
+        flags = p->flags;
+        trace_multifd_recv(p->id, p->packet_num, used, flags,
+                           p->next_packet_size);
+        p->num_packets++;
+        p->num_pages += used;
+        qemu_mutex_unlock(&p->mutex);
+
+        if (used) {
+            ret = qio_channel_readv_all(p->c, p->pages->iov,
+                                        used, &local_err);
+            if (ret != 0) {
+                break;
+            }
+        }
+
+        if (flags & MULTIFD_FLAG_SYNC) {
+            qemu_sem_post(&multifd_recv_state->sem_sync);
+            qemu_sem_wait(&p->sem_sync);
+        }
+    }
+
+    if (local_err) {
+        multifd_recv_terminate_threads(local_err);
+    }
+    qemu_mutex_lock(&p->mutex);
+    p->running = false;
+    qemu_mutex_unlock(&p->mutex);
+
+    rcu_unregister_thread();
+    trace_multifd_recv_thread_end(p->id, p->num_packets, p->num_pages);
+
+    return NULL;
+}
+
+int multifd_load_setup(Error **errp)
+{
+    int thread_count;
+    uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    uint8_t i;
+
+    if (!migrate_use_multifd()) {
+        return 0;
+    }
+    thread_count = migrate_multifd_channels();
+    multifd_recv_state = g_malloc0(sizeof(*multifd_recv_state));
+    multifd_recv_state->params = g_new0(MultiFDRecvParams, thread_count);
+    atomic_set(&multifd_recv_state->count, 0);
+    qemu_sem_init(&multifd_recv_state->sem_sync, 0);
+
+    for (i = 0; i < thread_count; i++) {
+        MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+        qemu_mutex_init(&p->mutex);
+        qemu_sem_init(&p->sem_sync, 0);
+        p->quit = false;
+        p->id = i;
+        p->pages = multifd_pages_init(page_count);
+        p->packet_len = sizeof(MultiFDPacket_t)
+                      + sizeof(uint64_t) * page_count;
+        p->packet = g_malloc0(p->packet_len);
+        p->name = g_strdup_printf("multifdrecv_%d", i);
+    }
+    return 0;
+}
+
+bool multifd_recv_all_channels_created(void)
+{
+    int thread_count = migrate_multifd_channels();
+
+    if (!migrate_use_multifd()) {
+        return true;
+    }
+
+    return thread_count == atomic_read(&multifd_recv_state->count);
+}
+
+/*
+ * Try to receive all multifd channels to get ready for the migration.
+ * - Return true and do not set @errp when correctly receving all channels;
+ * - Return false and do not set @errp when correctly receiving the current one;
+ * - Return false and set @errp when failing to receive the current channel.
+ */
+bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
+{
+    MultiFDRecvParams *p;
+    Error *local_err = NULL;
+    int id;
+
+    id = multifd_recv_initial_packet(ioc, &local_err);
+    if (id < 0) {
+        multifd_recv_terminate_threads(local_err);
+        error_propagate_prepend(errp, local_err,
+                                "failed to receive packet"
+                                " via multifd channel %d: ",
+                                atomic_read(&multifd_recv_state->count));
+        return false;
+    }
+    trace_multifd_recv_new_channel(id);
+
+    p = &multifd_recv_state->params[id];
+    if (p->c != NULL) {
+        error_setg(&local_err, "multifd: received id '%d' already setup'",
+                   id);
+        multifd_recv_terminate_threads(local_err);
+        error_propagate(errp, local_err);
+        return false;
+    }
+    p->c = ioc;
+    object_ref(OBJECT(ioc));
+    /* initial packet */
+    p->num_packets = 1;
+
+    p->running = true;
+    qemu_thread_create(&p->thread, p->name, multifd_recv_thread, p,
+                       QEMU_THREAD_JOINABLE);
+    atomic_inc(&multifd_recv_state->count);
+    return atomic_read(&multifd_recv_state->count) ==
+           migrate_multifd_channels();
+}
+