]> git.proxmox.com Git - mirror_qemu.git/blobdiff - blockdev.c
virtio: decrement vq->inuse in virtqueue_discard()
[mirror_qemu.git] / blockdev.c
index 3eb05d1a90568081eace11cb2906d3ec69014e95..21614004d1744200f42e727789b748a50c51ee2c 100644 (file)
@@ -56,6 +56,8 @@
 static QTAILQ_HEAD(, BlockDriverState) monitor_bdrv_states =
     QTAILQ_HEAD_INITIALIZER(monitor_bdrv_states);
 
+static int do_open_tray(const char *device, bool force, Error **errp);
+
 static const char *const if_name[IF_COUNT] = {
     [IF_NONE] = "none",
     [IF_IDE] = "ide",
@@ -73,7 +75,7 @@ static int if_max_devs[IF_COUNT] = {
      * Do not change these numbers!  They govern how drive option
      * index maps to unit and bus.  That mapping is ABI.
      *
-     * All controllers used to imlement if=T drives need to support
+     * All controllers used to implement if=T drives need to support
      * if_max_devs[T] units, for any T with if_max_devs[T] != 0.
      * Otherwise, some index values map to "impossible" bus, unit
      * values.
@@ -469,6 +471,7 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
     int bdrv_flags = 0;
     int on_read_error, on_write_error;
     bool account_invalid, account_failed;
+    bool writethrough;
     BlockBackend *blk;
     BlockDriverState *bs;
     ThrottleConfig cfg;
@@ -507,6 +510,10 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
     account_invalid = qemu_opt_get_bool(opts, "stats-account-invalid", true);
     account_failed = qemu_opt_get_bool(opts, "stats-account-failed", true);
 
+    writethrough = !qemu_opt_get_bool(opts, BDRV_OPT_CACHE_WB, true);
+
+    id = qemu_opts_id(opts);
+
     qdict_extract_subqdict(bs_opts, &interval_dict, "stats-intervals.");
     qdict_array_split(interval_dict, &interval_list);
 
@@ -564,25 +571,12 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
     if ((!file || !*file) && !qdict_size(bs_opts)) {
         BlockBackendRootState *blk_rs;
 
-        blk = blk_new(errp);
-        if (!blk) {
-            goto early_err;
-        }
-
+        blk = blk_new();
         blk_rs = blk_get_root_state(blk);
         blk_rs->open_flags    = bdrv_flags;
         blk_rs->read_only     = !(bdrv_flags & BDRV_O_RDWR);
         blk_rs->detect_zeroes = detect_zeroes;
 
-        if (throttle_enabled(&cfg)) {
-            if (!throttling_group) {
-                throttling_group = blk_name(blk);
-            }
-            blk_rs->throttle_group = g_strdup(throttling_group);
-            blk_rs->throttle_state = throttle_group_incref(throttling_group);
-            blk_rs->throttle_state->cfg = cfg;
-        }
-
         QDECREF(bs_opts);
     } else {
         if (file && !*file) {
@@ -592,9 +586,9 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
         /* bdrv_open() defaults to the values in bdrv_flags (for compatibility
          * with other callers) rather than what we want as the real defaults.
          * Apply the defaults here instead. */
-        qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_WB, "on");
         qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_DIRECT, "off");
         qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_NO_FLUSH, "off");
+        assert((bdrv_flags & BDRV_O_CACHE_MASK) == 0);
 
         if (runstate_check(RUN_STATE_INMIGRATE)) {
             bdrv_flags |= BDRV_O_INACTIVE;
@@ -608,15 +602,6 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
 
         bs->detect_zeroes = detect_zeroes;
 
-        /* disk I/O throttling */
-        if (throttle_enabled(&cfg)) {
-            if (!throttling_group) {
-                throttling_group = blk_name(blk);
-            }
-            bdrv_io_limits_enable(bs, throttling_group);
-            bdrv_set_io_limits(bs, &cfg);
-        }
-
         if (bdrv_key_required(bs)) {
             autostart = 0;
         }
@@ -630,9 +615,19 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
         }
     }
 
+    /* disk I/O throttling */
+    if (throttle_enabled(&cfg)) {
+        if (!throttling_group) {
+            throttling_group = id;
+        }
+        blk_io_limits_enable(blk, throttling_group);
+        blk_set_io_limits(blk, &cfg);
+    }
+
+    blk_set_enable_write_cache(blk, !writethrough);
     blk_set_on_error(blk, on_read_error, on_write_error);
 
-    if (!monitor_add_blk(blk, qemu_opts_id(opts), errp)) {
+    if (!monitor_add_blk(blk, id, errp)) {
         blk_unref(blk);
         blk = NULL;
         goto err_no_bs_opts;
@@ -662,7 +657,6 @@ static BlockDriverState *bds_tree_init(QDict *bs_opts, Error **errp)
     QemuOpts *opts;
     Error *local_error = NULL;
     BlockdevDetectZeroesOptions detect_zeroes;
-    int ret;
     int bdrv_flags = 0;
 
     opts = qemu_opts_create(&qemu_root_bds_opts, NULL, 1, errp);
@@ -686,7 +680,6 @@ static BlockDriverState *bds_tree_init(QDict *bs_opts, Error **errp)
     /* bdrv_open() defaults to the values in bdrv_flags (for compatibility
      * with other callers) rather than what we want as the real defaults.
      * Apply the defaults here instead. */
-    qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_WB, "on");
     qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_DIRECT, "off");
     qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_NO_FLUSH, "off");
 
@@ -694,9 +687,8 @@ static BlockDriverState *bds_tree_init(QDict *bs_opts, Error **errp)
         bdrv_flags |= BDRV_O_INACTIVE;
     }
 
-    bs = NULL;
-    ret = bdrv_open(&bs, NULL, NULL, bs_opts, bdrv_flags, errp);
-    if (ret < 0) {
+    bs = bdrv_open(NULL, NULL, bs_opts, bdrv_flags, errp);
+    if (!bs) {
         goto fail_no_bs_opts;
     }
 
@@ -894,8 +886,9 @@ DriveInfo *drive_new(QemuOpts *all_opts, BlockInterfaceType block_default_type)
     value = qemu_opt_get(all_opts, "cache");
     if (value) {
         int flags = 0;
+        bool writethrough;
 
-        if (bdrv_parse_cache_flags(value, &flags) != 0) {
+        if (bdrv_parse_cache_mode(value, &flags, &writethrough) != 0) {
             error_report("invalid cache option");
             return NULL;
         }
@@ -903,7 +896,7 @@ DriveInfo *drive_new(QemuOpts *all_opts, BlockInterfaceType block_default_type)
         /* Specific options take precedence */
         if (!qemu_opt_get(all_opts, BDRV_OPT_CACHE_WB)) {
             qemu_opt_set_bool(all_opts, BDRV_OPT_CACHE_WB,
-                              !!(flags & BDRV_O_CACHE_WB), &error_abort);
+                              !writethrough, &error_abort);
         }
         if (!qemu_opt_get(all_opts, BDRV_OPT_CACHE_DIRECT)) {
             qemu_opt_set_bool(all_opts, BDRV_OPT_CACHE_DIRECT,
@@ -1648,7 +1641,7 @@ typedef struct ExternalSnapshotState {
 static void external_snapshot_prepare(BlkActionState *common,
                                       Error **errp)
 {
-    int flags = 0, ret;
+    int flags = 0;
     QDict *options = NULL;
     Error *local_err = NULL;
     /* Device and node name of the image to generate the snapshot from */
@@ -1743,6 +1736,7 @@ static void external_snapshot_prepare(BlkActionState *common,
         }
 
         flags = state->old_bs->open_flags;
+        flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ);
 
         /* create new image w/backing file */
         mode = s->has_mode ? s->mode : NEW_IMAGE_MODE_ABSOLUTE_PATHS;
@@ -1772,17 +1766,16 @@ static void external_snapshot_prepare(BlkActionState *common,
         flags |= BDRV_O_NO_BACKING;
     }
 
-    assert(state->new_bs == NULL);
-    ret = bdrv_open(&state->new_bs, new_image_file, snapshot_ref, options,
-                    flags, errp);
+    state->new_bs = bdrv_open(new_image_file, snapshot_ref, options, flags,
+                              errp);
     /* We will manually add the backing_hd field to the bs later */
-    if (ret != 0) {
+    if (!state->new_bs) {
         return;
     }
 
-    if (state->new_bs->blk != NULL) {
+    if (bdrv_has_blk(state->new_bs)) {
         error_setg(errp, "The snapshot is already in use by %s",
-                   blk_name(state->new_bs->blk));
+                   bdrv_get_parent_name(state->new_bs));
         return;
     }
 
@@ -1813,8 +1806,10 @@ static void external_snapshot_commit(BlkActionState *common)
     /* We don't need (or want) to use the transactional
      * bdrv_reopen_multiple() across all the entries at once, because we
      * don't want to abort all of them if one of them fails the reopen */
-    bdrv_reopen(state->old_bs, state->old_bs->open_flags & ~BDRV_O_RDWR,
-                NULL);
+    if (!state->old_bs->copy_on_read) {
+        bdrv_reopen(state->old_bs, state->old_bs->open_flags & ~BDRV_O_RDWR,
+                    NULL);
+    }
 }
 
 static void external_snapshot_abort(BlkActionState *common)
@@ -1843,9 +1838,9 @@ typedef struct DriveBackupState {
     BlockJob *job;
 } DriveBackupState;
 
-static void do_drive_backup(const char *device, const char *target,
-                            bool has_format, const char *format,
-                            enum MirrorSyncMode sync,
+static void do_drive_backup(const char *job_id, const char *device,
+                            const char *target, bool has_format,
+                            const char *format, enum MirrorSyncMode sync,
                             bool has_mode, enum NewImageMode mode,
                             bool has_speed, int64_t speed,
                             bool has_bitmap, const char *bitmap,
@@ -1883,7 +1878,8 @@ static void drive_backup_prepare(BlkActionState *common, Error **errp)
     bdrv_drained_begin(blk_bs(blk));
     state->bs = blk_bs(blk);
 
-    do_drive_backup(backup->device, backup->target,
+    do_drive_backup(backup->has_job_id ? backup->job_id : NULL,
+                    backup->device, backup->target,
                     backup->has_format, backup->format,
                     backup->sync,
                     backup->has_mode, backup->mode,
@@ -1928,8 +1924,8 @@ typedef struct BlockdevBackupState {
     AioContext *aio_context;
 } BlockdevBackupState;
 
-static void do_blockdev_backup(const char *device, const char *target,
-                               enum MirrorSyncMode sync,
+static void do_blockdev_backup(const char *job_id, const char *device,
+                               const char *target, enum MirrorSyncMode sync,
                                bool has_speed, int64_t speed,
                                bool has_on_source_error,
                                BlockdevOnError on_source_error,
@@ -1941,7 +1937,8 @@ static void blockdev_backup_prepare(BlkActionState *common, Error **errp)
 {
     BlockdevBackupState *state = DO_UPCAST(BlockdevBackupState, common, common);
     BlockdevBackup *backup;
-    BlockBackend *blk, *target;
+    BlockBackend *blk;
+    BlockDriverState *target;
     Error *local_err = NULL;
 
     assert(common->action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_BACKUP);
@@ -1958,15 +1955,14 @@ static void blockdev_backup_prepare(BlkActionState *common, Error **errp)
         return;
     }
 
-    target = blk_by_name(backup->target);
+    target = bdrv_lookup_bs(backup->target, backup->target, errp);
     if (!target) {
-        error_setg(errp, "Device '%s' not found", backup->target);
         return;
     }
 
     /* AioContext is released in .clean() */
     state->aio_context = blk_get_aio_context(blk);
-    if (state->aio_context != blk_get_aio_context(target)) {
+    if (state->aio_context != bdrv_get_aio_context(target)) {
         state->aio_context = NULL;
         error_setg(errp, "Backup between two IO threads is not implemented");
         return;
@@ -1975,8 +1971,8 @@ static void blockdev_backup_prepare(BlkActionState *common, Error **errp)
     state->bs = blk_bs(blk);
     bdrv_drained_begin(state->bs);
 
-    do_blockdev_backup(backup->device, backup->target,
-                       backup->sync,
+    do_blockdev_backup(backup->has_job_id ? backup->job_id : NULL,
+                       backup->device, backup->target, backup->sync,
                        backup->has_speed, backup->speed,
                        backup->has_on_source_error, backup->on_source_error,
                        backup->has_on_target_error, backup->on_target_error,
@@ -2286,12 +2282,18 @@ exit:
 void qmp_eject(const char *device, bool has_force, bool force, Error **errp)
 {
     Error *local_err = NULL;
+    int rc;
 
-    qmp_blockdev_open_tray(device, has_force, force, &local_err);
-    if (local_err) {
+    if (!has_force) {
+        force = false;
+    }
+
+    rc = do_open_tray(device, force, &local_err);
+    if (rc && rc != -ENOSYS) {
         error_propagate(errp, local_err);
         return;
     }
+    error_free(local_err);
 
     qmp_x_blockdev_remove_medium(device, errp);
 }
@@ -2320,35 +2322,41 @@ void qmp_block_passwd(bool has_device, const char *device,
     aio_context_release(aio_context);
 }
 
-void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
-                            Error **errp)
+/*
+ * Attempt to open the tray of @device.
+ * If @force, ignore its tray lock.
+ * Else, if the tray is locked, don't open it, but ask the guest to open it.
+ * On error, store an error through @errp and return -errno.
+ * If @device does not exist, return -ENODEV.
+ * If it has no removable media, return -ENOTSUP.
+ * If it has no tray, return -ENOSYS.
+ * If the guest was asked to open the tray, return -EINPROGRESS.
+ * Else, return 0.
+ */
+static int do_open_tray(const char *device, bool force, Error **errp)
 {
     BlockBackend *blk;
     bool locked;
 
-    if (!has_force) {
-        force = false;
-    }
-
     blk = blk_by_name(device);
     if (!blk) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
                   "Device '%s' not found", device);
-        return;
+        return -ENODEV;
     }
 
     if (!blk_dev_has_removable_media(blk)) {
         error_setg(errp, "Device '%s' is not removable", device);
-        return;
+        return -ENOTSUP;
     }
 
     if (!blk_dev_has_tray(blk)) {
-        /* Ignore this command on tray-less devices */
-        return;
+        error_setg(errp, "Device '%s' does not have a tray", device);
+        return -ENOSYS;
     }
 
     if (blk_dev_is_tray_open(blk)) {
-        return;
+        return 0;
     }
 
     locked = blk_dev_is_medium_locked(blk);
@@ -2359,6 +2367,31 @@ void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
     if (!locked || force) {
         blk_dev_change_media_cb(blk, false);
     }
+
+    if (locked && !force) {
+        error_setg(errp, "Device '%s' is locked and force was not specified, "
+                   "wait for tray to open and try again", device);
+        return -EINPROGRESS;
+    }
+
+    return 0;
+}
+
+void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
+                            Error **errp)
+{
+    Error *local_err = NULL;
+    int rc;
+
+    if (!has_force) {
+        force = false;
+    }
+    rc = do_open_tray(device, force, &local_err);
+    if (rc && rc != -ENOSYS && rc != -EINPROGRESS) {
+        error_propagate(errp, local_err);
+        return;
+    }
+    error_free(local_err);
 }
 
 void qmp_blockdev_close_tray(const char *device, Error **errp)
@@ -2496,9 +2529,9 @@ void qmp_x_blockdev_insert_medium(const char *device, const char *node_name,
         return;
     }
 
-    if (bs->blk) {
+    if (bdrv_has_blk(bs)) {
         error_setg(errp, "Node '%s' is already in use by '%s'", node_name,
-                   blk_name(bs->blk));
+                   bdrv_get_parent_name(bs));
         return;
     }
 
@@ -2513,7 +2546,8 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
 {
     BlockBackend *blk;
     BlockDriverState *medium_bs = NULL;
-    int bdrv_flags, ret;
+    int bdrv_flags;
+    int rc;
     QDict *options = NULL;
     Error *err = NULL;
 
@@ -2557,25 +2591,24 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
         qdict_put(options, "driver", qstring_from_str(format));
     }
 
-    assert(!medium_bs);
-    ret = bdrv_open(&medium_bs, filename, NULL, options, bdrv_flags, errp);
-    if (ret < 0) {
+    medium_bs = bdrv_open(filename, NULL, options, bdrv_flags, errp);
+    if (!medium_bs) {
         goto fail;
     }
 
-    blk_apply_root_state(blk, medium_bs);
-
     bdrv_add_key(medium_bs, NULL, &err);
     if (err) {
         error_propagate(errp, err);
         goto fail;
     }
 
-    qmp_blockdev_open_tray(device, false, false, &err);
-    if (err) {
+    rc = do_open_tray(device, false, &err);
+    if (rc && rc != -ENOSYS) {
         error_propagate(errp, err);
         goto fail;
     }
+    error_free(err);
+    err = NULL;
 
     qmp_x_blockdev_remove_medium(device, &err);
     if (err) {
@@ -2589,6 +2622,8 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
         goto fail;
     }
 
+    blk_apply_root_state(blk, medium_bs);
+
     qmp_blockdev_close_tray(device, errp);
 
 fail:
@@ -2599,49 +2634,17 @@ fail:
 }
 
 /* throttling disk I/O limits */
-void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
-                               int64_t bps_wr,
-                               int64_t iops,
-                               int64_t iops_rd,
-                               int64_t iops_wr,
-                               bool has_bps_max,
-                               int64_t bps_max,
-                               bool has_bps_rd_max,
-                               int64_t bps_rd_max,
-                               bool has_bps_wr_max,
-                               int64_t bps_wr_max,
-                               bool has_iops_max,
-                               int64_t iops_max,
-                               bool has_iops_rd_max,
-                               int64_t iops_rd_max,
-                               bool has_iops_wr_max,
-                               int64_t iops_wr_max,
-                               bool has_bps_max_length,
-                               int64_t bps_max_length,
-                               bool has_bps_rd_max_length,
-                               int64_t bps_rd_max_length,
-                               bool has_bps_wr_max_length,
-                               int64_t bps_wr_max_length,
-                               bool has_iops_max_length,
-                               int64_t iops_max_length,
-                               bool has_iops_rd_max_length,
-                               int64_t iops_rd_max_length,
-                               bool has_iops_wr_max_length,
-                               int64_t iops_wr_max_length,
-                               bool has_iops_size,
-                               int64_t iops_size,
-                               bool has_group,
-                               const char *group, Error **errp)
+void qmp_block_set_io_throttle(BlockIOThrottle *arg, Error **errp)
 {
     ThrottleConfig cfg;
     BlockDriverState *bs;
     BlockBackend *blk;
     AioContext *aio_context;
 
-    blk = blk_by_name(device);
+    blk = blk_by_name(arg->device);
     if (!blk) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
-                  "Device '%s' not found", device);
+                  "Device '%s' not found", arg->device);
         return;
     }
 
@@ -2650,59 +2653,59 @@ void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
 
     bs = blk_bs(blk);
     if (!bs) {
-        error_setg(errp, "Device '%s' has no medium", device);
+        error_setg(errp, "Device '%s' has no medium", arg->device);
         goto out;
     }
 
     throttle_config_init(&cfg);
-    cfg.buckets[THROTTLE_BPS_TOTAL].avg = bps;
-    cfg.buckets[THROTTLE_BPS_READ].avg  = bps_rd;
-    cfg.buckets[THROTTLE_BPS_WRITE].avg = bps_wr;
+    cfg.buckets[THROTTLE_BPS_TOTAL].avg = arg->bps;
+    cfg.buckets[THROTTLE_BPS_READ].avg  = arg->bps_rd;
+    cfg.buckets[THROTTLE_BPS_WRITE].avg = arg->bps_wr;
 
-    cfg.buckets[THROTTLE_OPS_TOTAL].avg = iops;
-    cfg.buckets[THROTTLE_OPS_READ].avg  = iops_rd;
-    cfg.buckets[THROTTLE_OPS_WRITE].avg = iops_wr;
+    cfg.buckets[THROTTLE_OPS_TOTAL].avg = arg->iops;
+    cfg.buckets[THROTTLE_OPS_READ].avg  = arg->iops_rd;
+    cfg.buckets[THROTTLE_OPS_WRITE].avg = arg->iops_wr;
 
-    if (has_bps_max) {
-        cfg.buckets[THROTTLE_BPS_TOTAL].max = bps_max;
+    if (arg->has_bps_max) {
+        cfg.buckets[THROTTLE_BPS_TOTAL].max = arg->bps_max;
     }
-    if (has_bps_rd_max) {
-        cfg.buckets[THROTTLE_BPS_READ].max = bps_rd_max;
+    if (arg->has_bps_rd_max) {
+        cfg.buckets[THROTTLE_BPS_READ].max = arg->bps_rd_max;
     }
-    if (has_bps_wr_max) {
-        cfg.buckets[THROTTLE_BPS_WRITE].max = bps_wr_max;
+    if (arg->has_bps_wr_max) {
+        cfg.buckets[THROTTLE_BPS_WRITE].max = arg->bps_wr_max;
     }
-    if (has_iops_max) {
-        cfg.buckets[THROTTLE_OPS_TOTAL].max = iops_max;
+    if (arg->has_iops_max) {
+        cfg.buckets[THROTTLE_OPS_TOTAL].max = arg->iops_max;
     }
-    if (has_iops_rd_max) {
-        cfg.buckets[THROTTLE_OPS_READ].max = iops_rd_max;
+    if (arg->has_iops_rd_max) {
+        cfg.buckets[THROTTLE_OPS_READ].max = arg->iops_rd_max;
     }
-    if (has_iops_wr_max) {
-        cfg.buckets[THROTTLE_OPS_WRITE].max = iops_wr_max;
+    if (arg->has_iops_wr_max) {
+        cfg.buckets[THROTTLE_OPS_WRITE].max = arg->iops_wr_max;
     }
 
-    if (has_bps_max_length) {
-        cfg.buckets[THROTTLE_BPS_TOTAL].burst_length = bps_max_length;
+    if (arg->has_bps_max_length) {
+        cfg.buckets[THROTTLE_BPS_TOTAL].burst_length = arg->bps_max_length;
     }
-    if (has_bps_rd_max_length) {
-        cfg.buckets[THROTTLE_BPS_READ].burst_length = bps_rd_max_length;
+    if (arg->has_bps_rd_max_length) {
+        cfg.buckets[THROTTLE_BPS_READ].burst_length = arg->bps_rd_max_length;
     }
-    if (has_bps_wr_max_length) {
-        cfg.buckets[THROTTLE_BPS_WRITE].burst_length = bps_wr_max_length;
+    if (arg->has_bps_wr_max_length) {
+        cfg.buckets[THROTTLE_BPS_WRITE].burst_length = arg->bps_wr_max_length;
     }
-    if (has_iops_max_length) {
-        cfg.buckets[THROTTLE_OPS_TOTAL].burst_length = iops_max_length;
+    if (arg->has_iops_max_length) {
+        cfg.buckets[THROTTLE_OPS_TOTAL].burst_length = arg->iops_max_length;
     }
-    if (has_iops_rd_max_length) {
-        cfg.buckets[THROTTLE_OPS_READ].burst_length = iops_rd_max_length;
+    if (arg->has_iops_rd_max_length) {
+        cfg.buckets[THROTTLE_OPS_READ].burst_length = arg->iops_rd_max_length;
     }
-    if (has_iops_wr_max_length) {
-        cfg.buckets[THROTTLE_OPS_WRITE].burst_length = iops_wr_max_length;
+    if (arg->has_iops_wr_max_length) {
+        cfg.buckets[THROTTLE_OPS_WRITE].burst_length = arg->iops_wr_max_length;
     }
 
-    if (has_iops_size) {
-        cfg.op_size = iops_size;
+    if (arg->has_iops_size) {
+        cfg.op_size = arg->iops_size;
     }
 
     if (!throttle_is_valid(&cfg, errp)) {
@@ -2712,16 +2715,17 @@ void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
     if (throttle_enabled(&cfg)) {
         /* Enable I/O limits if they're not enabled yet, otherwise
          * just update the throttling group. */
-        if (!bs->throttle_state) {
-            bdrv_io_limits_enable(bs, has_group ? group : device);
-        } else if (has_group) {
-            bdrv_io_limits_update_group(bs, group);
+        if (!blk_get_public(blk)->throttle_state) {
+            blk_io_limits_enable(blk,
+                                 arg->has_group ? arg->group : arg->device);
+        } else if (arg->has_group) {
+            blk_io_limits_update_group(blk, arg->group);
         }
         /* Set the new throttling configuration */
-        bdrv_set_io_limits(bs, &cfg);
-    } else if (bs->throttle_state) {
+        blk_set_io_limits(blk, &cfg);
+    } else if (blk_get_public(blk)->throttle_state) {
         /* If all throttling settings are set to 0, disable I/O limits */
-        bdrv_io_limits_disable(bs);
+        blk_io_limits_disable(blk);
     }
 
 out:
@@ -2869,9 +2873,6 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
 
     /* Make the BlockBackend and the attached BlockDriverState anonymous */
     monitor_remove_blk(blk);
-    if (blk_bs(blk)) {
-        bdrv_make_anon(blk_bs(blk));
-    }
 
     /* If this BlockBackend has a device attached to it, its refcount will be
      * decremented when the device is removed; otherwise we have to do so here.
@@ -2975,7 +2976,7 @@ static void block_job_cb(void *opaque, int ret)
     }
 }
 
-void qmp_block_stream(const char *device,
+void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
                       bool has_base, const char *base,
                       bool has_backing_file, const char *backing_file,
                       bool has_speed, int64_t speed,
@@ -3034,8 +3035,8 @@ void qmp_block_stream(const char *device,
     /* backing_file string overrides base bs filename */
     base_name = has_backing_file ? backing_file : base_name;
 
-    stream_start(bs, base_bs, base_name, has_speed ? speed : 0,
-                 on_error, block_job_cb, bs, &local_err);
+    stream_start(has_job_id ? job_id : NULL, bs, base_bs, base_name,
+                 has_speed ? speed : 0, on_error, block_job_cb, bs, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         goto out;
@@ -3047,7 +3048,7 @@ out:
     aio_context_release(aio_context);
 }
 
-void qmp_block_commit(const char *device,
+void qmp_block_commit(bool has_job_id, const char *job_id, const char *device,
                       bool has_base, const char *base,
                       bool has_top, const char *top,
                       bool has_backing_file, const char *backing_file,
@@ -3138,10 +3139,11 @@ void qmp_block_commit(const char *device,
                              " but 'top' is the active layer");
             goto out;
         }
-        commit_active_start(bs, base_bs, speed, on_error, block_job_cb,
-                            bs, &local_err);
+        commit_active_start(has_job_id ? job_id : NULL, bs, base_bs, speed,
+                            on_error, block_job_cb, bs, &local_err);
     } else {
-        commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs,
+        commit_start(has_job_id ? job_id : NULL, bs, base_bs, top_bs, speed,
+                     on_error, block_job_cb, bs,
                      has_backing_file ? backing_file : NULL, &local_err);
     }
     if (local_err != NULL) {
@@ -3153,9 +3155,9 @@ out:
     aio_context_release(aio_context);
 }
 
-static void do_drive_backup(const char *device, const char *target,
-                            bool has_format, const char *format,
-                            enum MirrorSyncMode sync,
+static void do_drive_backup(const char *job_id, const char *device,
+                            const char *target, bool has_format,
+                            const char *format, enum MirrorSyncMode sync,
                             bool has_mode, enum NewImageMode mode,
                             bool has_speed, int64_t speed,
                             bool has_bitmap, const char *bitmap,
@@ -3175,7 +3177,6 @@ static void do_drive_backup(const char *device, const char *target,
     Error *local_err = NULL;
     int flags;
     int64_t size;
-    int ret;
 
     if (!has_speed) {
         speed = 0;
@@ -3259,10 +3260,8 @@ static void do_drive_backup(const char *device, const char *target,
         qdict_put(options, "driver", qstring_from_str(format));
     }
 
-    target_bs = NULL;
-    ret = bdrv_open(&target_bs, target, NULL, options, flags, &local_err);
-    if (ret < 0) {
-        error_propagate(errp, local_err);
+    target_bs = bdrv_open(target, NULL, options, flags, errp);
+    if (!target_bs) {
         goto out;
     }
 
@@ -3277,11 +3276,11 @@ static void do_drive_backup(const char *device, const char *target,
         }
     }
 
-    backup_start(bs, target_bs, speed, sync, bmap,
+    backup_start(job_id, bs, target_bs, speed, sync, bmap,
                  on_source_error, on_target_error,
                  block_job_cb, bs, txn, &local_err);
+    bdrv_unref(target_bs);
     if (local_err != NULL) {
-        bdrv_unref(target_bs);
         error_propagate(errp, local_err);
         goto out;
     }
@@ -3290,7 +3289,8 @@ out:
     aio_context_release(aio_context);
 }
 
-void qmp_drive_backup(const char *device, const char *target,
+void qmp_drive_backup(bool has_job_id, const char *job_id,
+                      const char *device, const char *target,
                       bool has_format, const char *format,
                       enum MirrorSyncMode sync,
                       bool has_mode, enum NewImageMode mode,
@@ -3300,7 +3300,8 @@ void qmp_drive_backup(const char *device, const char *target,
                       bool has_on_target_error, BlockdevOnError on_target_error,
                       Error **errp)
 {
-    return do_drive_backup(device, target, has_format, format, sync,
+    return do_drive_backup(has_job_id ? job_id : NULL, device, target,
+                           has_format, format, sync,
                            has_mode, mode, has_speed, speed,
                            has_bitmap, bitmap,
                            has_on_source_error, on_source_error,
@@ -3313,8 +3314,8 @@ BlockDeviceInfoList *qmp_query_named_block_nodes(Error **errp)
     return bdrv_named_nodes_list(errp);
 }
 
-void do_blockdev_backup(const char *device, const char *target,
-                         enum MirrorSyncMode sync,
+void do_blockdev_backup(const char *job_id, const char *device,
+                        const char *target, enum MirrorSyncMode sync,
                          bool has_speed, int64_t speed,
                          bool has_on_source_error,
                          BlockdevOnError on_source_error,
@@ -3322,7 +3323,7 @@ void do_blockdev_backup(const char *device, const char *target,
                          BlockdevOnError on_target_error,
                          BlockJobTxn *txn, Error **errp)
 {
-    BlockBackend *blk, *target_blk;
+    BlockBackend *blk;
     BlockDriverState *bs;
     BlockDriverState *target_bs;
     Error *local_err = NULL;
@@ -3353,31 +3354,33 @@ void do_blockdev_backup(const char *device, const char *target,
     }
     bs = blk_bs(blk);
 
-    target_blk = blk_by_name(target);
-    if (!target_blk) {
-        error_setg(errp, "Device '%s' not found", target);
+    target_bs = bdrv_lookup_bs(target, target, errp);
+    if (!target_bs) {
         goto out;
     }
 
-    if (!blk_is_available(target_blk)) {
-        error_setg(errp, "Device '%s' has no medium", target);
-        goto out;
+    if (bdrv_get_aio_context(target_bs) != aio_context) {
+        if (!bdrv_has_blk(target_bs)) {
+            /* The target BDS is not attached, we can safely move it to another
+             * AioContext. */
+            bdrv_set_aio_context(target_bs, aio_context);
+        } else {
+            error_setg(errp, "Target is attached to a different thread from "
+                             "source.");
+            goto out;
+        }
     }
-    target_bs = blk_bs(target_blk);
-
-    bdrv_ref(target_bs);
-    bdrv_set_aio_context(target_bs, aio_context);
-    backup_start(bs, target_bs, speed, sync, NULL, on_source_error,
+    backup_start(job_id, bs, target_bs, speed, sync, NULL, on_source_error,
                  on_target_error, block_job_cb, bs, txn, &local_err);
     if (local_err != NULL) {
-        bdrv_unref(target_bs);
         error_propagate(errp, local_err);
     }
 out:
     aio_context_release(aio_context);
 }
 
-void qmp_blockdev_backup(const char *device, const char *target,
+void qmp_blockdev_backup(bool has_job_id, const char *job_id,
+                         const char *device, const char *target,
                          enum MirrorSyncMode sync,
                          bool has_speed, int64_t speed,
                          bool has_on_source_error,
@@ -3386,7 +3389,8 @@ void qmp_blockdev_backup(const char *device, const char *target,
                          BlockdevOnError on_target_error,
                          Error **errp)
 {
-    do_blockdev_backup(device, target, sync, has_speed, speed,
+    do_blockdev_backup(has_job_id ? job_id : NULL, device, target,
+                       sync, has_speed, speed,
                        has_on_source_error, on_source_error,
                        has_on_target_error, on_target_error,
                        NULL, errp);
@@ -3395,10 +3399,11 @@ void qmp_blockdev_backup(const char *device, const char *target,
 /* Parameter check and block job starting for drive mirroring.
  * Caller should hold @device and @target's aio context (must be the same).
  **/
-static void blockdev_mirror_common(BlockDriverState *bs,
+static void blockdev_mirror_common(const char *job_id, BlockDriverState *bs,
                                    BlockDriverState *target,
                                    bool has_replaces, const char *replaces,
                                    enum MirrorSyncMode sync,
+                                   BlockMirrorBackingMode backing_mode,
                                    bool has_speed, int64_t speed,
                                    bool has_granularity, uint32_t granularity,
                                    bool has_buf_size, int64_t buf_size,
@@ -3446,10 +3451,6 @@ static void blockdev_mirror_common(BlockDriverState *bs,
     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_MIRROR_TARGET, errp)) {
         return;
     }
-    if (target->blk) {
-        error_setg(errp, "Cannot mirror to an attached block device");
-        return;
-    }
 
     if (!bs->backing && sync == MIRROR_SYNC_MODE_TOP) {
         sync = MIRROR_SYNC_MODE_FULL;
@@ -3458,41 +3459,30 @@ static void blockdev_mirror_common(BlockDriverState *bs,
     /* pass the node name to replace to mirror start since it's loose coupling
      * and will allow to check whether the node still exist at mirror completion
      */
-    mirror_start(bs, target,
+    mirror_start(job_id, bs, target,
                  has_replaces ? replaces : NULL,
-                 speed, granularity, buf_size, sync,
+                 speed, granularity, buf_size, sync, backing_mode,
                  on_source_error, on_target_error, unmap,
                  block_job_cb, bs, errp);
 }
 
-void qmp_drive_mirror(const char *device, const char *target,
-                      bool has_format, const char *format,
-                      bool has_node_name, const char *node_name,
-                      bool has_replaces, const char *replaces,
-                      enum MirrorSyncMode sync,
-                      bool has_mode, enum NewImageMode mode,
-                      bool has_speed, int64_t speed,
-                      bool has_granularity, uint32_t granularity,
-                      bool has_buf_size, int64_t buf_size,
-                      bool has_on_source_error, BlockdevOnError on_source_error,
-                      bool has_on_target_error, BlockdevOnError on_target_error,
-                      bool has_unmap, bool unmap,
-                      Error **errp)
+void qmp_drive_mirror(DriveMirror *arg, Error **errp)
 {
     BlockDriverState *bs;
     BlockBackend *blk;
     BlockDriverState *source, *target_bs;
     AioContext *aio_context;
+    BlockMirrorBackingMode backing_mode;
     Error *local_err = NULL;
     QDict *options = NULL;
     int flags;
     int64_t size;
-    int ret;
+    const char *format = arg->format;
 
-    blk = blk_by_name(device);
+    blk = blk_by_name(arg->device);
     if (!blk) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
-                  "Device '%s' not found", device);
+                  "Device '%s' not found", arg->device);
         return;
     }
 
@@ -3500,24 +3490,25 @@ void qmp_drive_mirror(const char *device, const char *target,
     aio_context_acquire(aio_context);
 
     if (!blk_is_available(blk)) {
-        error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
+        error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, arg->device);
         goto out;
     }
     bs = blk_bs(blk);
-    if (!has_mode) {
-        mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
+    if (!arg->has_mode) {
+        arg->mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
     }
 
-    if (!has_format) {
-        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
+    if (!arg->has_format) {
+        format = (arg->mode == NEW_IMAGE_MODE_EXISTING
+                  ? NULL : bs->drv->format_name);
     }
 
     flags = bs->open_flags | BDRV_O_RDWR;
     source = backing_bs(bs);
-    if (!source && sync == MIRROR_SYNC_MODE_TOP) {
-        sync = MIRROR_SYNC_MODE_FULL;
+    if (!source && arg->sync == MIRROR_SYNC_MODE_TOP) {
+        arg->sync = MIRROR_SYNC_MODE_FULL;
     }
-    if (sync == MIRROR_SYNC_MODE_NONE) {
+    if (arg->sync == MIRROR_SYNC_MODE_NONE) {
         source = bs;
     }
 
@@ -3527,18 +3518,18 @@ void qmp_drive_mirror(const char *device, const char *target,
         goto out;
     }
 
-    if (has_replaces) {
+    if (arg->has_replaces) {
         BlockDriverState *to_replace_bs;
         AioContext *replace_aio_context;
         int64_t replace_size;
 
-        if (!has_node_name) {
+        if (!arg->has_node_name) {
             error_setg(errp, "a node-name must be provided when replacing a"
                              " named node of the graph");
             goto out;
         }
 
-        to_replace_bs = check_to_replace_node(bs, replaces, &local_err);
+        to_replace_bs = check_to_replace_node(bs, arg->replaces, &local_err);
 
         if (!to_replace_bs) {
             error_propagate(errp, local_err);
@@ -3557,20 +3548,26 @@ void qmp_drive_mirror(const char *device, const char *target,
         }
     }
 
-    if ((sync == MIRROR_SYNC_MODE_FULL || !source)
-        && mode != NEW_IMAGE_MODE_EXISTING)
+    if (arg->mode == NEW_IMAGE_MODE_ABSOLUTE_PATHS) {
+        backing_mode = MIRROR_SOURCE_BACKING_CHAIN;
+    } else {
+        backing_mode = MIRROR_OPEN_BACKING_CHAIN;
+    }
+
+    if ((arg->sync == MIRROR_SYNC_MODE_FULL || !source)
+        && arg->mode != NEW_IMAGE_MODE_EXISTING)
     {
         /* create new image w/o backing file */
         assert(format);
-        bdrv_img_create(target, format,
+        bdrv_img_create(arg->target, format,
                         NULL, NULL, NULL, size, flags, &local_err, false);
     } else {
-        switch (mode) {
+        switch (arg->mode) {
         case NEW_IMAGE_MODE_EXISTING:
             break;
         case NEW_IMAGE_MODE_ABSOLUTE_PATHS:
             /* create new image with backing file */
-            bdrv_img_create(target, format,
+            bdrv_img_create(arg->target, format,
                             source->filename,
                             source->drv->format_name,
                             NULL, size, flags, &local_err, false);
@@ -3586,8 +3583,8 @@ void qmp_drive_mirror(const char *device, const char *target,
     }
 
     options = qdict_new();
-    if (has_node_name) {
-        qdict_put(options, "node-name", qstring_from_str(node_name));
+    if (arg->has_node_name) {
+        qdict_put(options, "node-name", qstring_from_str(arg->node_name));
     }
     if (format) {
         qdict_put(options, "driver", qstring_from_str(format));
@@ -3596,34 +3593,31 @@ void qmp_drive_mirror(const char *device, const char *target,
     /* Mirroring takes care of copy-on-write using the source's backing
      * file.
      */
-    target_bs = NULL;
-    ret = bdrv_open(&target_bs, target, NULL, options,
-                    flags | BDRV_O_NO_BACKING, &local_err);
-    if (ret < 0) {
-        error_propagate(errp, local_err);
+    target_bs = bdrv_open(arg->target, NULL, options,
+                          flags | BDRV_O_NO_BACKING, errp);
+    if (!target_bs) {
         goto out;
     }
 
     bdrv_set_aio_context(target_bs, aio_context);
 
-    blockdev_mirror_common(bs, target_bs,
-                           has_replaces, replaces, sync,
-                           has_speed, speed,
-                           has_granularity, granularity,
-                           has_buf_size, buf_size,
-                           has_on_source_error, on_source_error,
-                           has_on_target_error, on_target_error,
-                           has_unmap, unmap,
+    blockdev_mirror_common(arg->has_job_id ? arg->job_id : NULL, bs, target_bs,
+                           arg->has_replaces, arg->replaces, arg->sync,
+                           backing_mode, arg->has_speed, arg->speed,
+                           arg->has_granularity, arg->granularity,
+                           arg->has_buf_size, arg->buf_size,
+                           arg->has_on_source_error, arg->on_source_error,
+                           arg->has_on_target_error, arg->on_target_error,
+                           arg->has_unmap, arg->unmap,
                            &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-        bdrv_unref(target_bs);
-    }
+    bdrv_unref(target_bs);
+    error_propagate(errp, local_err);
 out:
     aio_context_release(aio_context);
 }
 
-void qmp_blockdev_mirror(const char *device, const char *target,
+void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
+                         const char *device, const char *target,
                          bool has_replaces, const char *replaces,
                          MirrorSyncMode sync,
                          bool has_speed, int64_t speed,
@@ -3639,6 +3633,7 @@ void qmp_blockdev_mirror(const char *device, const char *target,
     BlockBackend *blk;
     BlockDriverState *target_bs;
     AioContext *aio_context;
+    BlockMirrorBackingMode backing_mode = MIRROR_LEAVE_BACKING_CHAIN;
     Error *local_err = NULL;
 
     blk = blk_by_name(device);
@@ -3661,11 +3656,10 @@ void qmp_blockdev_mirror(const char *device, const char *target,
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
-    bdrv_ref(target_bs);
     bdrv_set_aio_context(target_bs, aio_context);
 
-    blockdev_mirror_common(bs, target_bs,
-                           has_replaces, replaces, sync,
+    blockdev_mirror_common(has_job_id ? job_id : NULL, bs, target_bs,
+                           has_replaces, replaces, sync, backing_mode,
                            has_speed, speed,
                            has_granularity, granularity,
                            has_buf_size, buf_size,
@@ -3673,50 +3667,33 @@ void qmp_blockdev_mirror(const char *device, const char *target,
                            has_on_target_error, on_target_error,
                            true, true,
                            &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-        bdrv_unref(target_bs);
-    }
+    error_propagate(errp, local_err);
 
     aio_context_release(aio_context);
 }
 
-/* Get the block job for a given device name and acquire its AioContext */
-static BlockJob *find_block_job(const char *device, AioContext **aio_context,
+/* Get a block job using its ID and acquire its AioContext */
+static BlockJob *find_block_job(const char *id, AioContext **aio_context,
                                 Error **errp)
 {
-    BlockBackend *blk;
-    BlockDriverState *bs;
+    BlockJob *job;
 
-    *aio_context = NULL;
+    assert(id != NULL);
 
-    blk = blk_by_name(device);
-    if (!blk) {
-        goto notfound;
-    }
+    *aio_context = NULL;
 
-    *aio_context = blk_get_aio_context(blk);
-    aio_context_acquire(*aio_context);
+    job = block_job_get(id);
 
-    if (!blk_is_available(blk)) {
-        goto notfound;
-    }
-    bs = blk_bs(blk);
-
-    if (!bs->job) {
-        goto notfound;
+    if (!job) {
+        error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
+                  "Block job '%s' not found", id);
+        return NULL;
     }
 
-    return bs->job;
+    *aio_context = blk_get_aio_context(job->blk);
+    aio_context_acquire(*aio_context);
 
-notfound:
-    error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
-              "No active block job on device '%s'", device);
-    if (*aio_context) {
-        aio_context_release(*aio_context);
-        *aio_context = NULL;
-    }
-    return NULL;
+    return job;
 }
 
 void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)
@@ -3784,6 +3761,7 @@ void qmp_block_job_resume(const char *device, Error **errp)
 
     job->user_paused = false;
     trace_qmp_block_job_resume(job);
+    block_job_iostatus_reset(job);
     block_job_resume(job);
     aio_context_release(aio_context);
 }
@@ -3886,9 +3864,7 @@ void qmp_change_backing_file(const char *device,
 
     if (ro) {
         bdrv_reopen(image_bs, open_flags, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err); /* will preserve prior errp */
-        }
+        error_propagate(errp, local_err);
     }
 
 out:
@@ -3928,10 +3904,10 @@ out:
 
 void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
 {
-    QmpOutputVisitor *ov = qmp_output_visitor_new();
     BlockDriverState *bs;
     BlockBackend *blk = NULL;
     QObject *obj;
+    Visitor *v = qmp_output_visitor_new(&obj);
     QDict *qdict;
     Error *local_err = NULL;
 
@@ -3950,14 +3926,13 @@ void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
         }
     }
 
-    visit_type_BlockdevOptions(qmp_output_get_visitor(ov), NULL, &options,
-                               &local_err);
+    visit_type_BlockdevOptions(v, NULL, &options, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         goto fail;
     }
 
-    obj = qmp_output_get_qobject(ov);
+    visit_complete(v, &obj);
     qdict = qobject_to_qdict(obj);
 
     qdict_flatten(qdict);
@@ -3998,7 +3973,7 @@ void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
     }
 
 fail:
-    qmp_output_visitor_cleanup(ov);
+    visit_free(v);
 }
 
 void qmp_x_blockdev_del(bool has_id, const char *id,
@@ -4023,6 +3998,11 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
             error_setg(errp, "Cannot find block backend %s", id);
             return;
         }
+        if (blk_legacy_dinfo(blk)) {
+            error_setg(errp, "Deleting block backend added with drive-add"
+                       " is not supported");
+            return;
+        }
         if (blk_get_refcnt(blk) > 1) {
             error_setg(errp, "Block backend %s is in use", id);
             return;
@@ -4030,15 +4010,15 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
         bs = blk_bs(blk);
         aio_context = blk_get_aio_context(blk);
     } else {
+        blk = NULL;
         bs = bdrv_find_node(node_name);
         if (!bs) {
             error_setg(errp, "Cannot find node %s", node_name);
             return;
         }
-        blk = bs->blk;
-        if (blk) {
+        if (bdrv_has_blk(bs)) {
             error_setg(errp, "Node %s is in use by %s",
-                       node_name, blk_name(blk));
+                       node_name, bdrv_get_parent_name(bs));
             return;
         }
         aio_context = bdrv_get_aio_context(bs);
@@ -4076,24 +4056,76 @@ out:
     aio_context_release(aio_context);
 }
 
-BlockJobInfoList *qmp_query_block_jobs(Error **errp)
+static BdrvChild *bdrv_find_child(BlockDriverState *parent_bs,
+                                  const char *child_name)
 {
-    BlockJobInfoList *head = NULL, **p_next = &head;
-    BlockDriverState *bs;
+    BdrvChild *child;
 
-    for (bs = bdrv_next(NULL); bs; bs = bdrv_next(bs)) {
-        AioContext *aio_context = bdrv_get_aio_context(bs);
+    QLIST_FOREACH(child, &parent_bs->children, next) {
+        if (strcmp(child->name, child_name) == 0) {
+            return child;
+        }
+    }
 
-        aio_context_acquire(aio_context);
+    return NULL;
+}
 
-        if (bs->job) {
-            BlockJobInfoList *elem = g_new0(BlockJobInfoList, 1);
-            elem->value = block_job_query(bs->job);
-            *p_next = elem;
-            p_next = &elem->next;
+void qmp_x_blockdev_change(const char *parent, bool has_child,
+                           const char *child, bool has_node,
+                           const char *node, Error **errp)
+{
+    BlockDriverState *parent_bs, *new_bs = NULL;
+    BdrvChild *p_child;
+
+    parent_bs = bdrv_lookup_bs(parent, parent, errp);
+    if (!parent_bs) {
+        return;
+    }
+
+    if (has_child == has_node) {
+        if (has_child) {
+            error_setg(errp, "The parameters child and node are in conflict");
+        } else {
+            error_setg(errp, "Either child or node must be specified");
+        }
+        return;
+    }
+
+    if (has_child) {
+        p_child = bdrv_find_child(parent_bs, child);
+        if (!p_child) {
+            error_setg(errp, "Node '%s' does not have child '%s'",
+                       parent, child);
+            return;
         }
+        bdrv_del_child(parent_bs, p_child, errp);
+    }
+
+    if (has_node) {
+        new_bs = bdrv_find_node(node);
+        if (!new_bs) {
+            error_setg(errp, "Node '%s' not found", node);
+            return;
+        }
+        bdrv_add_child(parent_bs, new_bs, errp);
+    }
+}
+
+BlockJobInfoList *qmp_query_block_jobs(Error **errp)
+{
+    BlockJobInfoList *head = NULL, **p_next = &head;
+    BlockJob *job;
 
+    for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+        BlockJobInfoList *elem = g_new0(BlockJobInfoList, 1);
+        AioContext *aio_context = blk_get_aio_context(job->blk);
+
+        aio_context_acquire(aio_context);
+        elem->value = block_job_query(job);
         aio_context_release(aio_context);
+
+        *p_next = elem;
+        p_next = &elem->next;
     }
 
     return head;
@@ -4115,6 +4147,10 @@ QemuOptsList qemu_common_drive_opts = {
             .name = "aio",
             .type = QEMU_OPT_STRING,
             .help = "host AIO implementation (threads, native)",
+        },{
+            .name = BDRV_OPT_CACHE_WB,
+            .type = QEMU_OPT_BOOL,
+            .help = "Enable writeback mode",
         },{
             .name = "format",
             .type = QEMU_OPT_STRING,