[Qemu-devel] [patch 6/7] QEMU live block copy

[Marcelo Tosatti]

Support live image copy + switch. That is, copy an image backing
a guest hard disk to a destination image (destination image must
be created separately), and switch to this copy.

Command syntax:

block_copy device filename [-i] -- live block copy device to image
             -i for incremental copy (base image shared between src and 
destination)

Please refer to qmp-commands diff for more details.

Signed-off-by: Marcelo Tosatti <address@hidden>

Index: qemu-block-copy/block-copy.c
===================================================================
--- /dev/null
+++ qemu-block-copy/block-copy.c
@@ -0,0 +1,764 @@
+/*
+ * QEMU live block copy
+ *
+ * Copyright (C) 2010 Red Hat Inc.
+ *
+ * Authors: Marcelo Tosatti <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "block_int.h"
+#include "blockdev.h"
+#include "qemu-queue.h"
+#include "qemu-timer.h"
+#include "monitor.h"
+#include "block-copy.h"
+#include "migration.h"
+#include "sysemu.h"
+#include "qjson.h"
+#include <assert.h>
+#include "hw/hw.h"
+
+#define BLOCK_SIZE (BDRV_SECTORS_PER_DIRTY_CHUNK << BDRV_SECTOR_BITS)
+#define MAX_IS_ALLOCATED_SEARCH 65536
+
+/*
+ * Stages:
+ *
+ * STAGE_BULK: bulk reads/writes in progress
+ * STAGE_BULK_FINISHED: bulk reads finished, bulk writes in progress
+ * STAGE_DIRTY: bulk writes finished, dirty reads/writes in progress
+ * STAGE_MIRROR_WRITES: copy finished, writes mirrored to both images.
+ * STAGE_SWITCH_FINISHED: switched to new image.
+ */
+
+enum BdrvCopyStage {
+    STAGE_BULK,
+    STAGE_BULK_FINISHED,
+    STAGE_DIRTY,
+    STAGE_MIRROR_WRITES,
+    STAGE_SWITCH_FINISHED,
+};
+
+#define NAME_LEN 1024
+#define DEV_LEN 256
+
+typedef struct BdrvCopyState {
+    BlockDriverState *src;
+    BlockDriverState *dst;
+    bool shared_base;
+
+    int64_t curr_sector;
+    int64_t completed_sectors;
+    int64_t nr_sectors;
+
+    enum BdrvCopyStage stage;
+    int inflight_reads;
+    int error;
+    int failed;
+    int cancelled;
+    QLIST_HEAD(, BdrvCopyBlock) io_list;
+    unsigned long *aio_bitmap;
+    QEMUTimer *aio_timer;
+    QLIST_ENTRY(BdrvCopyState) list;
+
+    int64_t blocks;
+    int64_t total_time;
+
+    char device_name[DEV_LEN];
+    char src_filename[NAME_LEN];
+    char dst_filename[NAME_LEN];
+} BdrvCopyState;
+
+typedef struct BdrvCopyBlock {
+    BdrvCopyState *state;
+    uint8_t *buf;
+    int64_t sector;
+    int64_t nr_sectors;
+    struct iovec iov;
+    QEMUIOVector qiov;
+    BlockDriverAIOCB *aiocb;
+    int64_t time;
+    QLIST_ENTRY(BdrvCopyBlock) list;
+} BdrvCopyBlock;
+
+static QLIST_HEAD(, BdrvCopyState) block_copy_list =
+    QLIST_HEAD_INITIALIZER(block_copy_list);
+
+static void alloc_aio_bitmap(BdrvCopyState *s)
+{
+    BlockDriverState *bs = s->src;
+    int64_t bitmap_size;
+
+    bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS) +
+            BDRV_SECTORS_PER_DIRTY_CHUNK * 8 - 1;
+    bitmap_size /= BDRV_SECTORS_PER_DIRTY_CHUNK * 8;
+
+    s->aio_bitmap = qemu_mallocz(bitmap_size);
+}
+
+static bool aio_inflight(BdrvCopyState *s, int64_t sector)
+{
+    int64_t chunk = sector / (int64_t)BDRV_SECTORS_PER_DIRTY_CHUNK;
+
+    if (s->aio_bitmap &&
+        (sector << BDRV_SECTOR_BITS) < bdrv_getlength(s->src)) {
+        return !!(s->aio_bitmap[chunk / (sizeof(unsigned long) * 8)] &
+            (1UL << (chunk % (sizeof(unsigned long) * 8))));
+    } else {
+        return 0;
+    }
+}
+
+static void set_aio_inflight(BdrvCopyState *s, int64_t sector_num,
+                             int nb_sectors, int set)
+{
+    int64_t start, end;
+    unsigned long val, idx, bit;
+
+    start = sector_num / BDRV_SECTORS_PER_DIRTY_CHUNK;
+    end = (sector_num + nb_sectors - 1) / BDRV_SECTORS_PER_DIRTY_CHUNK;
+
+    for (; start <= end; start++) {
+        idx = start / (sizeof(unsigned long) * 8);
+        bit = start % (sizeof(unsigned long) * 8);
+        val = s->aio_bitmap[idx];
+        if (set) {
+            if (!(val & (1UL << bit))) {
+                val |= 1UL << bit;
+            }
+        } else {
+            if (val & (1UL << bit)) {
+                val &= ~(1UL << bit);
+            }
+        }
+        s->aio_bitmap[idx] = val;
+    }
+}
+
+static void blkcopy_set_stage(BdrvCopyState *s, enum BdrvCopyStage stage)
+{
+    s->stage = stage;
+
+    switch (stage) {
+    case STAGE_BULK:
+        BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_STAGE_BULK);
+        break;
+    case STAGE_BULK_FINISHED:
+        BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_STAGE_BULK_FINISHED);
+        break;
+    case STAGE_DIRTY:
+        BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_STAGE_DIRTY);
+        break;
+    case STAGE_MIRROR_WRITES:
+        BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_STAGE_MIRROR_WRITES);
+        break;
+    case STAGE_SWITCH_FINISHED:
+        BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_STAGE_SWITCH_FINISHED);
+        break;
+    default:
+        break;
+    }
+}
+
+static void blk_copy_handle_cb_error(BdrvCopyState *s, int ret)
+{
+    s->error = ret;
+    qemu_mod_timer(s->aio_timer, qemu_get_clock_ms(rt_clock));
+}
+
+static inline void add_avg_transfer_time(BdrvCopyState *s, int64_t time)
+{
+    s->blocks++;
+    s->total_time += time;
+}
+
+static void blk_copy_write_cb(void *opaque, int ret)
+{
+    BdrvCopyBlock *blk = opaque;
+    BdrvCopyState *s = blk->state;
+
+    if (ret < 0) {
+        QLIST_REMOVE(blk, list);
+        qemu_free(blk->buf);
+        qemu_free(blk);
+        blk_copy_handle_cb_error(s, ret);
+        return;
+    }
+
+    QLIST_REMOVE(blk, list);
+    add_avg_transfer_time(s, qemu_get_clock_ns(rt_clock) - blk->time);
+
+    /* schedule switch to STAGE_DIRTY on last bulk write completion */
+    if (blk->state->stage == STAGE_BULK_FINISHED) {
+        qemu_mod_timer(s->aio_timer, qemu_get_clock_ms(rt_clock));
+    }
+
+    if (blk->state->stage > STAGE_BULK_FINISHED) {
+        set_aio_inflight(blk->state, blk->sector, blk->nr_sectors, 0);
+    }
+
+    qemu_free(blk->buf);
+    qemu_free(blk);
+}
+
+static void blk_copy_issue_write(BdrvCopyState *s, BdrvCopyBlock *read_blk)
+{
+    BdrvCopyBlock *blk = qemu_mallocz(sizeof(BdrvCopyBlock));
+    blk->state = s;
+    blk->sector = read_blk->sector;
+    blk->nr_sectors = read_blk->nr_sectors;
+    blk->time = read_blk->time;
+    blk->buf = read_blk->buf;
+    QLIST_INSERT_HEAD(&s->io_list, blk, list);
+
+    blk->iov.iov_base = read_blk->buf;
+    blk->iov.iov_len = read_blk->iov.iov_len;
+    qemu_iovec_init_external(&blk->qiov, &blk->iov, 1);
+
+    BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_AIO_WRITE);
+    blk->aiocb = bdrv_aio_writev(s->dst, blk->sector, &blk->qiov,
+                                 blk->iov.iov_len / BDRV_SECTOR_SIZE,
+                                 blk_copy_write_cb, blk);
+    if (!blk->aiocb) {
+        s->error = 1;
+        goto error;
+    }
+
+    return;
+
+error:
+    QLIST_REMOVE(blk, list);
+    qemu_free(read_blk->buf);
+    qemu_free(blk);
+}
+
+static void blk_copy_read_cb(void *opaque, int ret)
+{
+    BdrvCopyBlock *blk = opaque;
+    BdrvCopyState *s = blk->state;
+
+    s->inflight_reads--;
+    if (ret < 0) {
+        QLIST_REMOVE(blk, list);
+        qemu_free(blk->buf);
+        qemu_free(blk);
+        blk_copy_handle_cb_error(s, ret);
+        return;
+    }
+    blk_copy_issue_write(s, blk);
+    QLIST_REMOVE(blk, list);
+    qemu_free(blk);
+    qemu_mod_timer(s->aio_timer, qemu_get_clock_ms(rt_clock));
+}
+
+static void blk_copy_issue_read(BdrvCopyState *s, int64_t sector,
+                                int nr_sectors)
+{
+    BdrvCopyBlock *blk = qemu_mallocz(sizeof(BdrvCopyBlock));
+    blk->buf = qemu_mallocz(BLOCK_SIZE);
+    blk->state = s;
+    blk->sector = sector;
+    blk->nr_sectors = nr_sectors;
+    QLIST_INSERT_HEAD(&s->io_list, blk, list);
+
+    blk->iov.iov_base = blk->buf;
+    blk->iov.iov_len = nr_sectors * BDRV_SECTOR_SIZE;
+    qemu_iovec_init_external(&blk->qiov, &blk->iov, 1);
+
+    s->inflight_reads++;
+    blk->time = qemu_get_clock_ns(rt_clock);
+    blk->aiocb = bdrv_aio_readv(s->src, sector, &blk->qiov, nr_sectors,
+                                blk_copy_read_cb, blk);
+    if (!blk->aiocb) {
+        s->error = 1;
+        goto error;
+    }
+
+    return;
+
+error:
+    s->inflight_reads--;
+    QLIST_REMOVE(blk, list);
+    qemu_free(blk->buf);
+    qemu_free(blk);
+}
+
+static bool blkcopy_can_switch(BdrvCopyState *s)
+{
+    int64_t remaining_dirty;
+    int64_t avg_transfer_time;
+
+    remaining_dirty = bdrv_get_dirty_count(s->src);
+    if (remaining_dirty == 0 || s->blocks == 0) {
+        return true;
+    }
+
+    avg_transfer_time = s->total_time / s->blocks;
+    if ((remaining_dirty * avg_transfer_time) <= migrate_max_downtime()) {
+        return true;
+    }
+    return false;
+}
+
+static int blk_issue_reads_dirty(BdrvCopyState *s)
+{
+    int64_t sector;
+
+    for (sector = s->curr_sector; sector < s->nr_sectors;) {
+        if (bdrv_get_dirty(s->src, sector) && !aio_inflight(s, sector)) {
+            int nr_sectors = MIN(s->nr_sectors - s->curr_sector,
+                                 BDRV_SECTORS_PER_DIRTY_CHUNK);
+
+            blk_copy_issue_read(s, sector, nr_sectors);
+            bdrv_reset_dirty(s->src, sector, nr_sectors);
+            set_aio_inflight(s, sector, nr_sectors, 1);
+            break;
+        }
+
+        sector += BDRV_SECTORS_PER_DIRTY_CHUNK;
+        s->curr_sector = sector;
+    }
+
+    if (sector >= s->nr_sectors) {
+        s->curr_sector = 0;
+    }
+    return 0;
+}
+
+static int blk_issue_reads_bulk(BdrvCopyState *s)
+{
+    int nr_sectors;
+    int64_t curr_sector = s->curr_sector;
+
+    if (s->shared_base) {
+        while (curr_sector < s->nr_sectors &&
+                !bdrv_is_allocated(s->src, curr_sector,
+                                   MAX_IS_ALLOCATED_SEARCH, &nr_sectors)) {
+                curr_sector += nr_sectors;
+        }
+    }
+
+    if (curr_sector >= s->nr_sectors) {
+        s->curr_sector = 0;
+        return 1;
+    }
+
+    curr_sector &= ~((int64_t)BDRV_SECTORS_PER_DIRTY_CHUNK - 1);
+    nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
+
+    blk_copy_issue_read(s, s->curr_sector, nr_sectors);
+    s->curr_sector += nr_sectors;
+    s->completed_sectors = curr_sector;
+    return 0;
+}
+
+static void blkcopy_finish(BdrvCopyState *s)
+{
+    int64_t sector;
+    uint8_t *buf;
+
+    buf = qemu_malloc(BLOCK_SIZE);
+
+    /* FIXME: speed up loop, get_next_dirty_block? */
+    for (sector = 0; sector < s->nr_sectors;
+         sector += BDRV_SECTORS_PER_DIRTY_CHUNK) {
+        if (bdrv_get_dirty(s->src, sector)) {
+            int nr_sectors = MIN(s->nr_sectors - sector,
+                                 BDRV_SECTORS_PER_DIRTY_CHUNK);
+
+            memset(buf, 0, BLOCK_SIZE);
+            if (bdrv_read(s->src, sector, buf, nr_sectors) < 0) {
+                goto error;
+            }
+            if (bdrv_write(s->dst, sector, buf, nr_sectors) < 0) {
+                goto error;
+            }
+            bdrv_reset_dirty(s->src, sector, nr_sectors);
+        }
+
+        if (bdrv_get_dirty_count(s->src) == 0) {
+            break;
+        }
+    }
+    qemu_free(buf);
+    return;
+
+error:
+    qemu_free(buf);
+    s->error = 1;
+}
+
+static void blkcopy_cleanup(BdrvCopyState *s)
+{
+    assert(s->inflight_reads == 0);
+    assert(QLIST_EMPTY(&s->io_list));
+    bdrv_set_dirty_tracking(s->src, 0);
+    drive_put_ref(drive_get_by_blockdev(s->src));
+    bdrv_set_in_use(s->src, 0);
+    if (s->stage >= STAGE_DIRTY) {
+        qemu_free(s->aio_bitmap);
+    }
+    qemu_del_timer(s->aio_timer);
+}
+
+static void blkcopy_free(BdrvCopyState *s)
+{
+    QLIST_REMOVE(s, list);
+    qemu_free(s);
+}
+
+static void handle_error(BdrvCopyState *s)
+{
+    if (!QLIST_EMPTY(&s->io_list)) {
+        return;
+    }
+    s->failed = 1;
+    blkcopy_cleanup(s);
+}
+
+static void blkcopy_switch(BdrvCopyState *s)
+{
+    char src_filename[NAME_LEN], mirror_name[NAME_LEN*2];
+    int open_flags, ret;
+
+    strncpy(src_filename, s->src->filename, sizeof(src_filename) - 1);
+    open_flags = s->src->open_flags;
+
+    assert(s->stage == STAGE_DIRTY);
+
+    vm_stop(VMSTOP_BLOCKCOPY);
+    /* flush any guest writes, dirty bitmap uptodate after this.
+     * copy AIO also finished.
+     */
+    qemu_aio_flush();
+    assert(QLIST_EMPTY(&s->io_list));
+    if (s->error) {
+        handle_error(s);
+        goto vm_start;
+    }
+    blkcopy_finish(s);
+    if (s->error) {
+        handle_error(s);
+        goto vm_start;
+    }
+    assert(bdrv_get_dirty_count(s->src) == 0);
+    /* turn dirty bitmap off */
+    bdrv_set_dirty_tracking(s->src, 0);
+    /* switch to double writes */
+    bdrv_flush_all();
+    bdrv_close(s->src);
+    bdrv_close(s->dst);
+
+    snprintf(mirror_name, sizeof(mirror_name)-1,
+             "blkmirror:%s:%s", s->dst->filename, s->src->filename);
+
+    ret = bdrv_open(s->src, mirror_name, s->src->open_flags, NULL);
+    if (ret < 0) {
+        error_report("%s: cannot open blkmirror device, err %d",
+                      mirror_name, ret);
+        s->failed = 1;
+        goto err;
+    }
+
+    blkcopy_set_stage(s, STAGE_MIRROR_WRITES);
+    qemu_del_timer(s->aio_timer);
+
+vm_start:
+    vm_start();
+    return;
+
+err:
+    if (bdrv_open(s->src, src_filename, open_flags, NULL) < 0) {
+        error_report("%s: %s: cannot fallback to source image\n", __func__,
+                     s->src_filename);
+        abort();
+    }
+    blkcopy_cleanup(s);
+    goto vm_start;
+}
+
+#define BLKCOPY_INFLIGHT 2
+
+/*
+ * To simplify the implementation, the IO completion callbacks do not
+ * handle stage control or submit IO for further blocks. A timer is used
+ * for such purpose.
+ */
+
+static void aio_timer(void *opaque)
+{
+    BdrvCopyState *s = opaque;
+
+    assert(s->cancelled == 0);
+    assert(s->stage < STAGE_MIRROR_WRITES);
+
+    if (s->error) {
+        handle_error(s);
+        return;
+    }
+
+    while (s->stage == STAGE_BULK) {
+        if (s->inflight_reads >= BLKCOPY_INFLIGHT) {
+            break;
+        }
+        if (blk_issue_reads_bulk(s)) {
+            blkcopy_set_stage(s, STAGE_BULK_FINISHED);
+        }
+    }
+
+    if (s->stage == STAGE_BULK_FINISHED) {
+        if (QLIST_EMPTY(&s->io_list)) {
+            blkcopy_set_stage(s, STAGE_DIRTY);
+            alloc_aio_bitmap(s);
+        }
+    }
+
+    while (s->stage == STAGE_DIRTY) {
+        if (s->inflight_reads >= BLKCOPY_INFLIGHT) {
+            break;
+        }
+        blk_issue_reads_dirty(s);
+        if (blkcopy_can_switch(s)) {
+            BLKDBG_EVENT(s->dst->file, BLKDBG_BLKCOPY_SWITCH_START);
+            blkcopy_switch(s);
+            return;
+        }
+    }
+}
+
+
+int do_bdrv_copy_switch(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *device = qdict_get_str(qdict, "device");
+    BdrvCopyState *s = NULL;
+    int open_flags;
+
+    QLIST_FOREACH(s, &block_copy_list, list) {
+        if (!strcmp(s->device_name, device)) {
+            if (s->stage != STAGE_MIRROR_WRITES) {
+                qerror_report(QERR_IN_PROGRESS, "block copy");
+                return -1;
+            }
+            break;
+        }
+    }
+
+    if (!s) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, device);
+        return -1;
+    }
+
+    open_flags = s->src->open_flags;
+
+    /* switch from mirrored writes to destination only */
+    bdrv_flush_all();
+    bdrv_close(s->src);
+    if (bdrv_open(s->src, s->dst->filename, s->src->open_flags, NULL) < 0) {
+        s->failed = 1;
+        goto err;
+    }
+
+    blkcopy_set_stage(s, STAGE_SWITCH_FINISHED);
+    blkcopy_cleanup(s);
+    return 0;
+
+err:
+    if (bdrv_open(s->src, s->src_filename, open_flags, NULL) < 0) {
+        error_report("%s: %s: cannot fallback to source image\n", __func__,
+                     s->src_filename);
+        abort();
+    }
+    return -1;
+}
+
+static int bdrv_copy_setup(const char *device, const char *filename,
+                           bool shared_base)
+{
+    int64_t sectors;
+    BdrvCopyState *blkcopy, *safe;
+    BlockDriverState *src, *dst;
+
+    src = bdrv_find(device);
+    if (src) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, device);
+        return -1;
+    }
+
+    dst = bdrv_new("");
+    if (bdrv_open(dst, filename, src->open_flags, NULL) < 0) {
+        bdrv_delete(dst);
+        qerror_report(QERR_OPEN_FILE_FAILED, filename);
+        return -1;
+    }
+
+    QLIST_FOREACH_SAFE(blkcopy, &block_copy_list, list, safe) {
+        if (!strcmp(blkcopy->device_name, src->device_name)) {
+            if (blkcopy->stage == STAGE_SWITCH_FINISHED || blkcopy->failed) {
+                blkcopy_free(blkcopy);
+            } else {
+                qerror_report(QERR_IN_PROGRESS, "block copy");
+                return -1;
+            }
+        }
+    }
+
+    sectors = bdrv_getlength(src) >> BDRV_SECTOR_BITS;
+    if (sectors != bdrv_getlength(dst) >> BDRV_SECTOR_BITS) {
+        qerror_report(QERR_BLOCKCOPY_IMAGE_SIZE_DIFFERS);
+        return -1;
+    }
+
+    blkcopy = qemu_mallocz(sizeof(BdrvCopyState));
+    blkcopy->src = src;
+    blkcopy->dst = dst;
+    blkcopy->curr_sector = 0;
+    blkcopy->nr_sectors = sectors;
+    blkcopy_set_stage(blkcopy, STAGE_BULK);
+    blkcopy->aio_timer = qemu_new_timer_ms(rt_clock, aio_timer, blkcopy);
+    blkcopy->shared_base = shared_base;
+    strncpy(blkcopy->device_name, blkcopy->src->device_name,
+            sizeof(blkcopy->device_name) - 1);
+    strncpy(blkcopy->src_filename, blkcopy->src->filename,
+            sizeof(blkcopy->src_filename) - 1);
+    strncpy(blkcopy->dst_filename, filename,
+            sizeof(blkcopy->dst_filename) - 1);
+
+    drive_get_ref(drive_get_by_blockdev(src));
+    bdrv_set_in_use(src, 1);
+    bdrv_set_dirty_tracking(src, 1);
+    qemu_mod_timer(blkcopy->aio_timer, qemu_get_clock_ms(rt_clock));
+
+    QLIST_INSERT_HEAD(&block_copy_list, blkcopy, list);
+    return 0;
+}
+
+int do_bdrv_copy(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *device = qdict_get_str(qdict, "device");
+    const char *filename = qdict_get_str(qdict, "filename");
+    bool shared_base = qdict_get_try_bool(qdict, "incremental", 0);
+
+    if (migration_active()) {
+        qerror_report(QERR_IN_PROGRESS, "migration");
+        return -1;
+    }
+
+    return bdrv_copy_setup(device, filename, shared_base);
+}
+
+int do_bdrv_copy_cancel(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    BdrvCopyState *blkcopy, *s = NULL;
+    const char *device = qdict_get_str(qdict, "device");
+
+    QLIST_FOREACH(blkcopy, &block_copy_list, list) {
+        if (!strcmp(blkcopy->device_name, device)) {
+            s = blkcopy;
+            break;
+        }
+    }
+
+    if (!s || s->stage == STAGE_SWITCH_FINISHED || s->failed) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, device);
+        return -1;
+    }
+
+    s->cancelled = 1;
+    do {
+        qemu_aio_flush();
+    } while (!QLIST_EMPTY(&s->io_list));
+    blkcopy_cleanup(s);
+    blkcopy_free(s);
+
+    return 0;
+}
+
+static void blockcopy_print_dict(QObject *obj, void *opaque)
+{
+    QDict *c_dict;
+    Monitor *mon = opaque;
+
+    c_dict = qobject_to_qdict(obj);
+
+    monitor_printf(mon, "%s: status=%s ",
+                        qdict_get_str(c_dict, "device"),
+                        qdict_get_str(c_dict, "status"));
+
+    if (qdict_haskey(c_dict, "info")) {
+        QDict *qdict = qobject_to_qdict(qdict_get(c_dict, "info"));
+
+        monitor_printf(mon, "percentage=%ld %%",
+                       qdict_get_int(qdict, "percentage"));
+    }
+
+    monitor_printf(mon, "\n");
+}
+
+void do_info_blockcopy_print(Monitor *mon, const QObject *data)
+{
+    qlist_iter(qobject_to_qlist(data), blockcopy_print_dict, mon);
+}
+
+void do_info_blockcopy(Monitor *mon, QObject **ret_data)
+{
+    QList *c_list;
+    BdrvCopyState *s;
+
+    c_list = qlist_new();
+
+    QLIST_FOREACH(s, &block_copy_list, list) {
+        QObject *c_obj;
+        static const char *status[] = { "failed", "active", "mirrored",
+                                        "completed" };
+        int i;
+
+        if (s->failed) {
+            i = 0;
+        } else if (s->stage < STAGE_MIRROR_WRITES) {
+            i = 1;
+        } else if (s->stage < STAGE_SWITCH_FINISHED) {
+            i = 2;
+        } else {
+            i = 3;
+        }
+
+        c_obj = qobject_from_jsonf("{ 'device': %s, 'status': %s }",
+                                    s->device_name, status[i]);
+
+        if (i == 1) {
+            QDict *dict = qobject_to_qdict(c_obj);
+            QObject *obj;
+
+            /* FIXME: add dirty stage progress? */
+            obj = qobject_from_jsonf("{ 'percentage': %" PRId64 "}",
+                                     s->completed_sectors * 100
+                                     / s->nr_sectors);
+            qdict_put_obj(dict, "info", obj);
+        }
+        qlist_append_obj(c_list, c_obj);
+    }
+
+    *ret_data = QOBJECT(c_list);
+}
+
+bool block_copy_active(void)
+{
+    BdrvCopyState *s;
+
+    QLIST_FOREACH(s, &block_copy_list, list) {
+        if (s->failed) {
+            continue;
+        }
+        if (s->stage < STAGE_SWITCH_FINISHED) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
Index: qemu-block-copy/block-copy.h
===================================================================
--- /dev/null
+++ qemu-block-copy/block-copy.h
@@ -0,0 +1,26 @@
+/*
+ * QEMU live block copy
+ *
+ * Copyright (C) 2010 Red Hat Inc.
+ *
+ * Authors: Marcelo Tosatti <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef BLOCK_COPY_H
+#define BLOCK_COPY_H
+
+int do_bdrv_copy(Monitor *mon, const QDict *qdict, QObject **ret_data);
+int do_bdrv_copy_cancel(Monitor *mon, const QDict *qdict, QObject **ret_data);
+int do_bdrv_copy_switch(Monitor *mon, const QDict *qdict, QObject **ret_data);
+
+void do_info_blockcopy_print(Monitor *mon, const QObject *data);
+void do_info_blockcopy(Monitor *mon, QObject **ret_data);
+
+bool block_copy_active(void);
+
+#endif /* BLOCK_COPY_H */
+
Index: qemu-block-copy/hmp-commands.hx
===================================================================
--- qemu-block-copy.orig/hmp-commands.hx
+++ qemu-block-copy/hmp-commands.hx
@@ -806,6 +806,63 @@ Set maximum speed to @var{value} (in byt
 ETEXI
 
     {
+        .name       = "block_copy",
+        .args_type  = "device:s,filename:s,incremental:-i",
+        .params     = "device filename [-i]",
+        .help       = "live block copy device to image"
+                      "\n\t\t\t -i for incremental copy "
+                      "(base image shared between original and destination)",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy,
+    },
+
+STEXI
address@hidden block_copy @var{device} @var{filename} [-i]
address@hidden block_copy
+Live copy block device @var{device} to image @var{filename}.
+        -i for incremental copy (base image is shared)
+
+Destination image @var{filename} must be created with qemu-img prior
+to execution of this command, with image size equal to the original
+image size.
+
+Incremental copy allows the destination image @var{filename} to share
+a common base image with the original image. This option skips copying
+blocks which are not allocated in the original image.
+ETEXI
+
+    {
+        .name       = "block_copy_cancel",
+        .args_type  = "device:s",
+        .params     = "device",
+        .help       = "cancel live block copy",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy_cancel,
+    },
+
+STEXI
address@hidden block_copy_cancel @var{device}
address@hidden block_copy_cancel
+Cancel live block copy on @var{device}.
+ETEXI
+
+    {
+        .name       = "block_copy_switch",
+        .args_type  = "device:s",
+        .params     = "device",
+        .help       = "finish live block copy",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy_switch,
+    },
+
+STEXI
address@hidden block_copy_switch @var{device}
address@hidden block_copy_switch
+Finish live block copy on @var{device} by switching
+to destination image.
+ETEXI
+
+    {
         .name       = "migrate_set_downtime",
         .args_type  = "value:T",
         .params     = "value",
@@ -1352,6 +1409,8 @@ show device tree
 show qdev device model list
 @item info roms
 show roms
address@hidden info block-copy
+show block copy status
 @end table
 ETEXI
 
Index: qemu-block-copy/monitor.c
===================================================================
--- qemu-block-copy.orig/monitor.c
+++ qemu-block-copy/monitor.c
@@ -45,6 +45,7 @@
 #include "balloon.h"
 #include "qemu-timer.h"
 #include "migration.h"
+#include "block-copy.h"
 #include "kvm.h"
 #include "acl.h"
 #include "qint.h"
@@ -3101,6 +3102,14 @@ static const mon_cmd_t info_cmds[] = {
     },
 #endif
     {
+        .name       = "block-copy",
+        .args_type  = "",
+        .params     = "",
+        .help       = "show block copy status",
+        .user_print = do_info_blockcopy_print,
+        .mhandler.info_new = do_info_blockcopy,
+    },
+    {
         .name       = NULL,
     },
 };
@@ -3242,6 +3251,14 @@ static const mon_cmd_t qmp_query_cmds[] 
         .mhandler.info_async = do_info_balloon,
         .flags      = MONITOR_CMD_ASYNC,
     },
+    {
+        .name       = "block-copy",
+        .args_type  = "",
+        .params     = "",
+        .help       = "show block copy status",
+        .user_print = do_info_blockcopy_print,
+        .mhandler.info_new = do_info_blockcopy,
+    },
     { /* NULL */ },
 };
 
Index: qemu-block-copy/qmp-commands.hx
===================================================================
--- qemu-block-copy.orig/qmp-commands.hx
+++ qemu-block-copy/qmp-commands.hx
@@ -581,6 +581,98 @@ Example:
 EQMP
 
     {
+        .name       = "block_copy",
+        .args_type  = "device:s,filename:s,inc:-i",
+        .params     = "device filename [-i]",
+        .help       = "live block copy device to image"
+                      "\n\t\t\t -i for incremental copy "
+                      "(base image shared between src and destination)",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy,
+    },
+
+SQMP
+block-copy
+-------
+
+Live block copy.
+
+Arguments:
+
+- "device": device name (json-string)
+- "filename": target image filename (json-string)
+- "incremental": incremental disk copy (json-bool, optional)
+
+Example:
+
+-> { "execute": "block_copy",
+                            "arguments": { "device": "ide0-hd1",
+                               "filename": "/mnt/new-disk.img",
+                             } }
+
+<- { "return": {} }
+
+Notes:
+
+(1) The 'query-block-copy' command should be used to check block copy progress
+    and final result (this information is provided by the 'status' member)
+(2) Boolean argument "incremental" defaults to false
+
+EQMP
+
+    {
+        .name       = "block_copy_cancel",
+        .args_type  = "device:s",
+        .params     = "device",
+        .help       = "cancel live block copy",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy_cancel,
+    },
+
+SQMP
+block_copy_cancel
+--------------
+
+Cancel live block copy.
+
+Arguments:
+
+- device: device name (json-string)
+
+Example:
+
+-> { "execute": "block_copy_cancel", "arguments": { "device": "ide0-hd1" } }
+<- { "return": {} }
+
+EQMP
+
+    {
+        .name       = "block_copy_switch",
+        .args_type  = "device:s",
+        .params     = "device",
+        .help       = "finish live block copy",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_bdrv_copy_switch,
+    },
+
+SQMP
+block_copy_switch
+--------------
+
+Finish live block copy, switching device to destination image.
+
+Arguments:
+
+- device: device name (json-string)
+
+Example:
+
+-> { "execute": "block_copy_switch", "arguments": { "device": "ide0-hd1" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "netdev_add",
         .args_type  = "netdev:O",
         .params     = "[user|tap|socket],id=str[,prop=value][,...]",
@@ -1744,6 +1836,50 @@ Examples:
 EQMP
 
 SQMP
+query-block-copy
+-------------
+
+Live block copy status.
+
+Each block copy instance information is stored in a json-object and the 
returned
+value is a json-array of all instances.
+
+Each json-object contains the following:
+
+- "device": device name (json-string)
+- "status": block copy status (json-string)
+    - Possible values: "active", "failed", "mirrored", "completed", meaning:
+                    - failed: block copy failed.
+                    - active: block copy active, copying to destination image.
+                    - mirrored: block copy active, finished copying to 
destination
+                      image, writes are mirrored.
+                    - completed: block copy completed.
+
+- "info": A json-object with the statistics information, if status is "active":
+    - "percentage": percentage completed (json-int)
+
+Example:
+
+Block copy for "ide1-hd0" active and block copy for "ide1-hd1" failed:
+
+-> { "execute": "query-block-copy" }
+<- {
+      "return":[
+        {"device":"ide1-hd0",
+            "status":"active",
+            "info":{
+               "percentage":23,
+            }
+        },
+        {"device":"ide1-hd1",
+         "status":"failed"
+        }
+      ]
+   }
+
+EQMP
+
+SQMP
 query-balloon
 -------------
 
Index: qemu-block-copy/Makefile.objs
===================================================================
--- qemu-block-copy.orig/Makefile.objs
+++ qemu-block-copy/Makefile.objs
@@ -98,7 +98,7 @@ common-obj-y += buffered_file.o migratio
 common-obj-y += qemu-char.o savevm.o #aio.o
 common-obj-y += msmouse.o ps2.o
 common-obj-y += qdev.o qdev-properties.o
-common-obj-y += block-migration.o iohandler.o
+common-obj-y += block-migration.o iohandler.o block-copy.o
 common-obj-y += pflib.o
 common-obj-y += bitmap.o bitops.o
 
Index: qemu-block-copy/docs/block_copy.txt
===================================================================
--- /dev/null
+++ qemu-block-copy/docs/block_copy.txt
@@ -0,0 +1,39 @@
+Live block copy
+===============
+
+Block copy allows an image to be copied to a destination image, while
+the guest is operating on the source image. The command is:
+
+block_copy {device} {filename} [-i]
+
+Destination image {filename} must be created with qemu-img prior to
+execution of this command, with image size equal to the original image
+size.
+
+Incremental copy allows the destination image to share a common base
+image with the original image. This option skips copying blocks which
+are not allocated in the original image.
+
+
+Command flow
+============
+
+Once the copy initiated with the block_copy command has finished,
+writes by the guest to the source image will be mirrored to the
+destination image.
+
+This state is indicated by the "mirrored" status of a device, visible in
+query-block-copy command output.
+
+Once in the mirrored state, management application is able to issue
+the block_copy_switch command to complete the block copy operation.
+
+Follows a pseudo-algorithm:
+
+     block_copy(dev, file);
+     do {
+         query_block_copy(block_copy_state);
+         sleep(s)
+     } while (!block_copy_state.dev.mirrored);
+     block_copy_switch(dev);
+