Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- file-posix: Make auto-read-only dynamic
- Add x-blockdev-reopen QMP command
- Finalize block-latency-histogram QMP command
- gluster: Build fixes for newer lib version

# gpg: Signature made Tue 12 Mar 2019 19:30:31 GMT
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (28 commits)
  qemu-iotests: Test the x-blockdev-reopen QMP command
  block: Add an 'x-blockdev-reopen' QMP command
  block: Remove the AioContext parameter from bdrv_reopen_multiple()
  block: Add bdrv_reset_options_allowed()
  block: Add a 'mutable_opts' field to BlockDriver
  block: Allow changing the backing file on reopen
  block: Allow omitting the 'backing' option in certain cases
  block: Handle child references in bdrv_reopen_queue()
  block: Add 'keep_old_opts' parameter to bdrv_reopen_queue()
  block: Freeze the backing chain for the duration of the stream job
  block: Freeze the backing chain for the duration of the mirror job
  block: Freeze the backing chain for the duration of the commit job
  block: Allow freezing BdrvChild links
  nvme: fix write zeroes offset and count
  file-posix: Make auto-read-only dynamic
  file-posix: Prepare permission code for fd switching
  file-posix: Lock new fd in raw_reopen_prepare()
  file-posix: Store BDRVRawState.reopen_state during reopen
  file-posix: Factor out raw_reconfigure_getfd()
  file-posix: Fix bdrv_open_flags() for snapshot=on
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

26 files changed, 1929 insertions, 160 deletions

diff --git a/block.c b/block.c
index ccf008c177..ed9253c786 100644
--- a/block.c
+++ b/block.c
@@ -1163,13 +1163,6 @@ static int bdrv_open_flags(BlockDriverState *bs, int flags)
      */
     open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_PROTOCOL);
 
-    /*
-     * Snapshots should be writable.
-     */
-    if (flags & BDRV_O_TEMPORARY) {
-        open_flags |= BDRV_O_RDWR;
-    }
-
     return open_flags;
 }
 
@@ -1698,6 +1691,7 @@ static void bdrv_child_set_perm(BdrvChild *c, uint64_t perm, uint64_t shared);
 
 typedef struct BlockReopenQueueEntry {
      bool prepared;
+     bool perms_checked;
      BDRVReopenState state;
      QSIMPLEQ_ENTRY(BlockReopenQueueEntry) entry;
 } BlockReopenQueueEntry;
@@ -2132,6 +2126,8 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
     BlockDriverState *old_bs = child->bs;
     int i;
 
+    assert(!child->frozen);
+
     if (old_bs && new_bs) {
         assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs));
     }
@@ -2348,6 +2344,10 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
     bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
         bdrv_inherits_from_recursive(backing_hd, bs);
 
+    if (bdrv_is_backing_chain_frozen(bs, backing_bs(bs), errp)) {
+        return;
+    }
+
     if (backing_hd) {
         bdrv_ref(backing_hd);
     }
@@ -2983,6 +2983,74 @@ BlockDriverState *bdrv_open(const char *filename, const char *reference,
                              NULL, errp);
 }
 
+/* Return true if the NULL-terminated @list contains @str */
+static bool is_str_in_list(const char *str, const char *const *list)
+{
+    if (str && list) {
+        int i;
+        for (i = 0; list[i] != NULL; i++) {
+            if (!strcmp(str, list[i])) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+/*
+ * Check that every option set in @bs->options is also set in
+ * @new_opts.
+ *
+ * Options listed in the common_options list and in
+ * @bs->drv->mutable_opts are skipped.
+ *
+ * Return 0 on success, otherwise return -EINVAL and set @errp.
+ */
+static int bdrv_reset_options_allowed(BlockDriverState *bs,
+                                      const QDict *new_opts, Error **errp)
+{
+    const QDictEntry *e;
+    /* These options are common to all block drivers and are handled
+     * in bdrv_reopen_prepare() so they can be left out of @new_opts */
+    const char *const common_options[] = {
+        "node-name", "discard", "cache.direct", "cache.no-flush",
+        "read-only", "auto-read-only", "detect-zeroes", NULL
+    };
+
+    for (e = qdict_first(bs->options); e; e = qdict_next(bs->options, e)) {
+        if (!qdict_haskey(new_opts, e->key) &&
+            !is_str_in_list(e->key, common_options) &&
+            !is_str_in_list(e->key, bs->drv->mutable_opts)) {
+            error_setg(errp, "Option '%s' cannot be reset "
+                       "to its default value", e->key);
+            return -EINVAL;
+        }
+    }
+
+    return 0;
+}
+
+/*
+ * Returns true if @child can be reached recursively from @bs
+ */
+static bool bdrv_recurse_has_child(BlockDriverState *bs,
+                                   BlockDriverState *child)
+{
+    BdrvChild *c;
+
+    if (bs == child) {
+        return true;
+    }
+
+    QLIST_FOREACH(c, &bs->children, next) {
+        if (bdrv_recurse_has_child(c->bs, child)) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 /*
  * Adds a BlockDriverState to a simple queue for an atomic, transactional
  * reopen of multiple devices.
@@ -3010,7 +3078,8 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
                                                  QDict *options,
                                                  const BdrvChildRole *role,
                                                  QDict *parent_options,
-                                                 int parent_flags)
+                                                 int parent_flags,
+                                                 bool keep_old_opts)
 {
     assert(bs != NULL);
 
@@ -3050,13 +3119,13 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
      */
 
     /* Old explicitly set values (don't overwrite by inherited value) */
-    if (bs_entry) {
-        old_options = qdict_clone_shallow(bs_entry->state.explicit_options);
-    } else {
-        old_options = qdict_clone_shallow(bs->explicit_options);
+    if (bs_entry || keep_old_opts) {
+        old_options = qdict_clone_shallow(bs_entry ?
+                                          bs_entry->state.explicit_options :
+                                          bs->explicit_options);
+        bdrv_join_options(bs, options, old_options);
+        qobject_unref(old_options);
     }
-    bdrv_join_options(bs, options, old_options);
-    qobject_unref(old_options);
 
     explicit_options = qdict_clone_shallow(options);
 
@@ -3068,10 +3137,12 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
         flags = bdrv_get_flags(bs);
     }
 
-    /* Old values are used for options that aren't set yet */
-    old_options = qdict_clone_shallow(bs->options);
-    bdrv_join_options(bs, options, old_options);
-    qobject_unref(old_options);
+    if (keep_old_opts) {
+        /* Old values are used for options that aren't set yet */
+        old_options = qdict_clone_shallow(bs->options);
+        bdrv_join_options(bs, options, old_options);
+        qobject_unref(old_options);
+    }
 
     /* We have the final set of options so let's update the flags */
     options_copy = qdict_clone_shallow(options);
@@ -3104,9 +3175,21 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
     bs_entry->state.perm = UINT64_MAX;
     bs_entry->state.shared_perm = 0;
 
+    /*
+     * If keep_old_opts is false then it means that unspecified
+     * options must be reset to their original value. We don't allow
+     * resetting 'backing' but we need to know if the option is
+     * missing in order to decide if we have to return an error.
+     */
+    if (!keep_old_opts) {
+        bs_entry->state.backing_missing =
+            !qdict_haskey(options, "backing") &&
+            !qdict_haskey(options, "backing.driver");
+    }
+
     QLIST_FOREACH(child, &bs->children, next) {
-        QDict *new_child_options;
-        char *child_key_dot;
+        QDict *new_child_options = NULL;
+        bool child_keep_old = keep_old_opts;
 
         /* reopen can only change the options of block devices that were
          * implicitly created and inherited options. For other (referenced)
@@ -3115,13 +3198,32 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
             continue;
         }
 
-        child_key_dot = g_strdup_printf("%s.", child->name);
-        qdict_extract_subqdict(explicit_options, NULL, child_key_dot);
-        qdict_extract_subqdict(options, &new_child_options, child_key_dot);
-        g_free(child_key_dot);
+        /* Check if the options contain a child reference */
+        if (qdict_haskey(options, child->name)) {
+            const char *childref = qdict_get_try_str(options, child->name);
+            /*
+             * The current child must not be reopened if the child
+             * reference is null or points to a different node.
+             */
+            if (g_strcmp0(childref, child->bs->node_name)) {
+                continue;
+            }
+            /*
+             * If the child reference points to the current child then
+             * reopen it with its existing set of options (note that
+             * it can still inherit new options from the parent).
+             */
+            child_keep_old = true;
+        } else {
+            /* Extract child options ("child-name.*") */
+            char *child_key_dot = g_strdup_printf("%s.", child->name);
+            qdict_extract_subqdict(explicit_options, NULL, child_key_dot);
+            qdict_extract_subqdict(options, &new_child_options, child_key_dot);
+            g_free(child_key_dot);
+        }
 
         bdrv_reopen_queue_child(bs_queue, child->bs, new_child_options,
-                                child->role, options, flags);
+                                child->role, options, flags, child_keep_old);
     }
 
     return bs_queue;
@@ -3129,9 +3231,10 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
 
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
                                     BlockDriverState *bs,
-                                    QDict *options)
+                                    QDict *options, bool keep_old_opts)
 {
-    return bdrv_reopen_queue_child(bs_queue, bs, options, NULL, NULL, 0);
+    return bdrv_reopen_queue_child(bs_queue, bs, options, NULL, NULL, 0,
+                                   keep_old_opts);
 }
 
 /*
@@ -3151,23 +3254,44 @@ BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
  * All affected nodes must be drained between bdrv_reopen_queue() and
  * bdrv_reopen_multiple().
  */
-int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **errp)
+int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
 {
     int ret = -1;
     BlockReopenQueueEntry *bs_entry, *next;
-    Error *local_err = NULL;
 
     assert(bs_queue != NULL);
 
     QSIMPLEQ_FOREACH(bs_entry, bs_queue, entry) {
         assert(bs_entry->state.bs->quiesce_counter > 0);
-        if (bdrv_reopen_prepare(&bs_entry->state, bs_queue, &local_err)) {
-            error_propagate(errp, local_err);
+        if (bdrv_reopen_prepare(&bs_entry->state, bs_queue, errp)) {
             goto cleanup;
         }
         bs_entry->prepared = true;
     }
 
+    QSIMPLEQ_FOREACH(bs_entry, bs_queue, entry) {
+        BDRVReopenState *state = &bs_entry->state;
+        ret = bdrv_check_perm(state->bs, bs_queue, state->perm,
+                              state->shared_perm, NULL, errp);
+        if (ret < 0) {
+            goto cleanup_perm;
+        }
+        /* Check if new_backing_bs would accept the new permissions */
+        if (state->replace_backing_bs && state->new_backing_bs) {
+            uint64_t nperm, nshared;
+            bdrv_child_perm(state->bs, state->new_backing_bs,
+                            NULL, &child_backing, bs_queue,
+                            state->perm, state->shared_perm,
+                            &nperm, &nshared);
+            ret = bdrv_check_update_perm(state->new_backing_bs, NULL,
+                                         nperm, nshared, NULL, errp);
+            if (ret < 0) {
+                goto cleanup_perm;
+            }
+        }
+        bs_entry->perms_checked = true;
+    }
+
     /* If we reach this point, we have success and just need to apply the
      * changes
      */
@@ -3176,7 +3300,23 @@ int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **er
     }
 
     ret = 0;
+cleanup_perm:
+    QSIMPLEQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {
+        BDRVReopenState *state = &bs_entry->state;
+
+        if (!bs_entry->perms_checked) {
+            continue;
+        }
 
+        if (ret == 0) {
+            bdrv_set_perm(state->bs, state->perm, state->shared_perm);
+        } else {
+            bdrv_abort_perm_update(state->bs);
+            if (state->replace_backing_bs && state->new_backing_bs) {
+                bdrv_abort_perm_update(state->new_backing_bs);
+            }
+        }
+    }
 cleanup:
     QSIMPLEQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {
         if (ret) {
@@ -3186,6 +3326,9 @@ cleanup:
             qobject_unref(bs_entry->state.explicit_options);
             qobject_unref(bs_entry->state.options);
         }
+        if (bs_entry->state.new_backing_bs) {
+            bdrv_unref(bs_entry->state.new_backing_bs);
+        }
         g_free(bs_entry);
     }
     g_free(bs_queue);
@@ -3203,8 +3346,8 @@ int bdrv_reopen_set_read_only(BlockDriverState *bs, bool read_only,
     qdict_put_bool(opts, BDRV_OPT_READ_ONLY, read_only);
 
     bdrv_subtree_drained_begin(bs);
-    queue = bdrv_reopen_queue(NULL, bs, opts);
-    ret = bdrv_reopen_multiple(bdrv_get_aio_context(bs), queue, errp);
+    queue = bdrv_reopen_queue(NULL, bs, opts, true);
+    ret = bdrv_reopen_multiple(queue, errp);
     bdrv_subtree_drained_end(bs);
 
     return ret;
@@ -3258,6 +3401,101 @@ static void bdrv_reopen_perm(BlockReopenQueue *q, BlockDriverState *bs,
 }
 
 /*
+ * Take a BDRVReopenState and check if the value of 'backing' in the
+ * reopen_state->options QDict is valid or not.
+ *
+ * If 'backing' is missing from the QDict then return 0.
+ *
+ * If 'backing' contains the node name of the backing file of
+ * reopen_state->bs then return 0.
+ *
+ * If 'backing' contains a different node name (or is null) then check
+ * whether the current backing file can be replaced with the new one.
+ * If that's the case then reopen_state->replace_backing_bs is set to
+ * true and reopen_state->new_backing_bs contains a pointer to the new
+ * backing BlockDriverState (or NULL).
+ *
+ * Return 0 on success, otherwise return < 0 and set @errp.
+ */
+static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
+                                     Error **errp)
+{
+    BlockDriverState *bs = reopen_state->bs;
+    BlockDriverState *overlay_bs, *new_backing_bs;
+    QObject *value;
+    const char *str;
+
+    value = qdict_get(reopen_state->options, "backing");
+    if (value == NULL) {
+        return 0;
+    }
+
+    switch (qobject_type(value)) {
+    case QTYPE_QNULL:
+        new_backing_bs = NULL;
+        break;
+    case QTYPE_QSTRING:
+        str = qobject_get_try_str(value);
+        new_backing_bs = bdrv_lookup_bs(NULL, str, errp);
+        if (new_backing_bs == NULL) {
+            return -EINVAL;
+        } else if (bdrv_recurse_has_child(new_backing_bs, bs)) {
+            error_setg(errp, "Making '%s' a backing file of '%s' "
+                       "would create a cycle", str, bs->node_name);
+            return -EINVAL;
+        }
+        break;
+    default:
+        /* 'backing' does not allow any other data type */
+        g_assert_not_reached();
+    }
+
+    /*
+     * TODO: before removing the x- prefix from x-blockdev-reopen we
+     * should move the new backing file into the right AioContext
+     * instead of returning an error.
+     */
+    if (new_backing_bs) {
+        if (bdrv_get_aio_context(new_backing_bs) != bdrv_get_aio_context(bs)) {
+            error_setg(errp, "Cannot use a new backing file "
+                       "with a different AioContext");
+            return -EINVAL;
+        }
+    }
+
+    /*
+     * Find the "actual" backing file by skipping all links that point
+     * to an implicit node, if any (e.g. a commit filter node).
+     */
+    overlay_bs = bs;
+    while (backing_bs(overlay_bs) && backing_bs(overlay_bs)->implicit) {
+        overlay_bs = backing_bs(overlay_bs);
+    }
+
+    /* If we want to replace the backing file we need some extra checks */
+    if (new_backing_bs != backing_bs(overlay_bs)) {
+        /* Check for implicit nodes between bs and its backing file */
+        if (bs != overlay_bs) {
+            error_setg(errp, "Cannot change backing link if '%s' has "
+                       "an implicit backing file", bs->node_name);
+            return -EPERM;
+        }
+        /* Check if the backing link that we want to replace is frozen */
+        if (bdrv_is_backing_chain_frozen(overlay_bs, backing_bs(overlay_bs),
+                                         errp)) {
+            return -EPERM;
+        }
+        reopen_state->replace_backing_bs = true;
+        if (new_backing_bs) {
+            bdrv_ref(new_backing_bs);
+            reopen_state->new_backing_bs = new_backing_bs;
+        }
+    }
+
+    return 0;
+}
+
+/*
  * Prepares a BlockDriverState for reopen. All changes are staged in the
  * 'opaque' field of the BDRVReopenState, which is used and allocated by
  * the block driver layer .bdrv_reopen_prepare()
@@ -3355,6 +3593,17 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
     }
 
     if (drv->bdrv_reopen_prepare) {
+        /*
+         * If a driver-specific option is missing, it means that we
+         * should reset it to its default value.
+         * But not all options allow that, so we need to check it first.
+         */
+        ret = bdrv_reset_options_allowed(reopen_state->bs,
+                                         reopen_state->options, errp);
+        if (ret) {
+            goto error;
+        }
+
         ret = drv->bdrv_reopen_prepare(reopen_state, queue, &local_err);
         if (ret) {
             if (local_err != NULL) {
@@ -3378,6 +3627,30 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
 
     drv_prepared = true;
 
+    /*
+     * We must provide the 'backing' option if the BDS has a backing
+     * file or if the image file has a backing file name as part of
+     * its metadata. Otherwise the 'backing' option can be omitted.
+     */
+    if (drv->supports_backing && reopen_state->backing_missing &&
+        (backing_bs(reopen_state->bs) || reopen_state->bs->backing_file[0])) {
+        error_setg(errp, "backing is missing for '%s'",
+                   reopen_state->bs->node_name);
+        ret = -EINVAL;
+        goto error;
+    }
+
+    /*
+     * Allow changing the 'backing' option. The new value can be
+     * either a reference to an existing node (using its node name)
+     * or NULL to simply detach the current backing file.
+     */
+    ret = bdrv_reopen_parse_backing(reopen_state, errp);
+    if (ret < 0) {
+        goto error;
+    }
+    qdict_del(reopen_state->options, "backing");
+
     /* Options that are not handled are only okay if they are unchanged
      * compared to the old state. It is expected that some options are only
      * used for the initial open, but not reopen (e.g. filename) */
@@ -3430,12 +3703,6 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
         } while ((entry = qdict_next(reopen_state->options, entry)));
     }
 
-    ret = bdrv_check_perm(reopen_state->bs, queue, reopen_state->perm,
-                          reopen_state->shared_perm, NULL, errp);
-    if (ret < 0) {
-        goto error;
-    }
-
     ret = 0;
 
     /* Restore the original reopen_state->options QDict */
@@ -3493,6 +3760,11 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
     bs->read_only = !(reopen_state->flags & BDRV_O_RDWR);
     bs->detect_zeroes      = reopen_state->detect_zeroes;
 
+    if (reopen_state->replace_backing_bs) {
+        qdict_del(bs->explicit_options, "backing");
+        qdict_del(bs->options, "backing");
+    }
+
     /* Remove child references from bs->options and bs->explicit_options.
      * Child options were already removed in bdrv_reopen_queue_child() */
     QLIST_FOREACH(child, &bs->children, next) {
@@ -3500,10 +3772,22 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
         qdict_del(bs->options, child->name);
     }
 
-    bdrv_refresh_limits(bs, NULL);
+    /*
+     * Change the backing file if a new one was specified. We do this
+     * after updating bs->options, so bdrv_refresh_filename() (called
+     * from bdrv_set_backing_hd()) has the new values.
+     */
+    if (reopen_state->replace_backing_bs) {
+        BlockDriverState *old_backing_bs = backing_bs(bs);
+        assert(!old_backing_bs || !old_backing_bs->implicit);
+        /* Abort the permission update on the backing bs we're detaching */
+        if (old_backing_bs) {
+            bdrv_abort_perm_update(old_backing_bs);
+        }
+        bdrv_set_backing_hd(bs, reopen_state->new_backing_bs, &error_abort);
+    }
 
-    bdrv_set_perm(reopen_state->bs, reopen_state->perm,
-                  reopen_state->shared_perm);
+    bdrv_refresh_limits(bs, NULL);
 
     new_can_write =
         !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
@@ -3536,8 +3820,6 @@ void bdrv_reopen_abort(BDRVReopenState *reopen_state)
     if (drv->bdrv_reopen_abort) {
         drv->bdrv_reopen_abort(reopen_state);
     }
-
-    bdrv_abort_perm_update(reopen_state->bs);
 }
 
 
@@ -3717,6 +3999,11 @@ void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
         if (!should_update_child(c, to)) {
             continue;
         }
+        if (c->frozen) {
+            error_setg(errp, "Cannot change '%s' link to '%s'",
+                       c->name, from->node_name);
+            goto out;
+        }
         list = g_slist_prepend(list, c);
         perm |= c->perm;
         shared &= c->shared_perm;
@@ -3929,6 +4216,63 @@ BlockDriverState *bdrv_find_base(BlockDriverState *bs)
 }
 
 /*
+ * Return true if at least one of the backing links between @bs and
+ * @base is frozen. @errp is set if that's the case.
+ */
+bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+                                  Error **errp)
+{
+    BlockDriverState *i;
+
+    for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+        if (i->backing->frozen) {
+            error_setg(errp, "Cannot change '%s' link from '%s' to '%s'",
+                       i->backing->name, i->node_name,
+                       backing_bs(i)->node_name);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/*
+ * Freeze all backing links between @bs and @base.
+ * If any of the links is already frozen the operation is aborted and
+ * none of the links are modified.
+ * Returns 0 on success. On failure returns < 0 and sets @errp.
+ */
+int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
+                              Error **errp)
+{
+    BlockDriverState *i;
+
+    if (bdrv_is_backing_chain_frozen(bs, base, errp)) {
+        return -EPERM;
+    }
+
+    for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+        i->backing->frozen = true;
+    }
+
+    return 0;
+}
+
+/*
+ * Unfreeze all backing links between @bs and @base. The caller must
+ * ensure that all links are frozen before using this function.
+ */
+void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base)
+{
+    BlockDriverState *i;
+
+    for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+        assert(i->backing->frozen);
+        i->backing->frozen = false;
+    }
+}
+
+/*
  * Drops images above 'base' up to and including 'top', and sets the image
  * above 'top' to have base as its backing file.
  *
@@ -3977,6 +4321,14 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
         goto exit;
     }
 
+    /* This function changes all links that point to top and makes
+     * them point to base. Check that none of them is frozen. */
+    QLIST_FOREACH(c, &top->parents, next_parent) {
+        if (c->frozen) {
+            goto exit;
+        }
+    }
+
     /* If 'base' recursively inherits from 'top' then we should set
      * base->inherits_from to top->inherits_from after 'top' and all
      * other intermediate nodes have been dropped.
diff --git a/block/commit.c b/block/commit.c
index 3b46ca7f97..ba60fef58a 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -39,6 +39,7 @@ typedef struct CommitBlockJob {
     BlockDriverState *base_bs;
     BlockdevOnError on_error;
     bool base_read_only;
+    bool chain_frozen;
     char *backing_file_str;
 } CommitBlockJob;
 
@@ -68,6 +69,9 @@ static int commit_prepare(Job *job)
 {
     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 
+    bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
+    s->chain_frozen = false;
+
     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
      * the normal backing chain can be restored. */
     blk_unref(s->base);
@@ -84,6 +88,10 @@ static void commit_abort(Job *job)
     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
     BlockDriverState *top_bs = blk_bs(s->top);
 
+    if (s->chain_frozen) {
+        bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
+    }
+
     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
     bdrv_ref(top_bs);
     bdrv_ref(s->commit_top_bs);
@@ -330,6 +338,11 @@ void commit_start(const char *job_id, BlockDriverState *bs,
         }
     }
 
+    if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
+        goto fail;
+    }
+    s->chain_frozen = true;
+
     ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
     if (ret < 0) {
         goto fail;
@@ -362,6 +375,9 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     return;
 
 fail:
+    if (s->chain_frozen) {
+        bdrv_unfreeze_backing_chain(commit_top_bs, base);
+    }
     if (s->base) {
         blk_unref(s->base);
     }
diff --git a/block/file-posix.c b/block/file-posix.c
index ba6ab62a38..e9fa6aac48 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -144,6 +144,9 @@ typedef struct BDRVRawState {
     uint64_t locked_perm;
     uint64_t locked_shared_perm;
 
+    int perm_change_fd;
+    BDRVReopenState *reopen_state;
+
 #ifdef CONFIG_XFS
     bool is_xfs:1;
 #endif
@@ -373,13 +376,21 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp)
     }
 }
 
-static void raw_parse_flags(int bdrv_flags, int *open_flags)
+static void raw_parse_flags(int bdrv_flags, int *open_flags, bool has_writers)
 {
+    bool read_write = false;
     assert(open_flags != NULL);
 
     *open_flags |= O_BINARY;
     *open_flags &= ~O_ACCMODE;
-    if (bdrv_flags & BDRV_O_RDWR) {
+
+    if (bdrv_flags & BDRV_O_AUTO_RDONLY) {
+        read_write = has_writers;
+    } else if (bdrv_flags & BDRV_O_RDWR) {
+        read_write = true;
+    }
+
+    if (read_write) {
         *open_flags |= O_RDWR;
     } else {
         *open_flags |= O_RDONLY;
@@ -431,6 +442,8 @@ static QemuOptsList raw_runtime_opts = {
     },
 };
 
+static const char *const mutable_opts[] = { "x-check-cache-dropped", NULL };
+
 static int raw_open_common(BlockDriverState *bs, QDict *options,
                            int bdrv_flags, int open_flags,
                            bool device, Error **errp)
@@ -515,24 +528,12 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
                                                false);
 
     s->open_flags = open_flags;
-    raw_parse_flags(bdrv_flags, &s->open_flags);
+    raw_parse_flags(bdrv_flags, &s->open_flags, false);
 
     s->fd = -1;
     fd = qemu_open(filename, s->open_flags, 0644);
     ret = fd < 0 ? -errno : 0;
 
-    if (ret == -EACCES || ret == -EROFS) {
-        /* Try to degrade to read-only, but if it doesn't work, still use the
-         * normal error message. */
-        if (bdrv_apply_auto_read_only(bs, NULL, NULL) == 0) {
-            bdrv_flags &= ~BDRV_O_RDWR;
-            raw_parse_flags(bdrv_flags, &s->open_flags);
-            assert(!(s->open_flags & O_CREAT));
-            fd = qemu_open(filename, s->open_flags);
-            ret = fd < 0 ? -errno : 0;
-        }
-    }
-
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not open '%s'", filename);
         if (ret == -EROFS) {
@@ -842,13 +843,77 @@ static int raw_handle_perm_lock(BlockDriverState *bs,
     return ret;
 }
 
+static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
+                                 int *open_flags, uint64_t perm, bool force_dup,
+                                 Error **errp)
+{
+    BDRVRawState *s = bs->opaque;
+    int fd = -1;
+    int ret;
+    bool has_writers = perm &
+        (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED | BLK_PERM_RESIZE);
+    int fcntl_flags = O_APPEND | O_NONBLOCK;
+#ifdef O_NOATIME
+    fcntl_flags |= O_NOATIME;
+#endif
+
+    *open_flags = 0;
+    if (s->type == FTYPE_CD) {
+        *open_flags |= O_NONBLOCK;
+    }
+
+    raw_parse_flags(flags, open_flags, has_writers);
+
+#ifdef O_ASYNC
+    /* Not all operating systems have O_ASYNC, and those that don't
+     * will not let us track the state into rs->open_flags (typically
+     * you achieve the same effect with an ioctl, for example I_SETSIG
+     * on Solaris). But we do not use O_ASYNC, so that's fine.
+     */
+    assert((s->open_flags & O_ASYNC) == 0);
+#endif
+
+    if (!force_dup && *open_flags == s->open_flags) {
+        /* We're lucky, the existing fd is fine */
+        return s->fd;
+    }
+
+    if ((*open_flags & ~fcntl_flags) == (s->open_flags & ~fcntl_flags)) {
+        /* dup the original fd */
+        fd = qemu_dup(s->fd);
+        if (fd >= 0) {
+            ret = fcntl_setfl(fd, *open_flags);
+            if (ret) {
+                qemu_close(fd);
+                fd = -1;
+            }
+        }
+    }
+
+    /* If we cannot use fcntl, or fcntl failed, fall back to qemu_open() */
+    if (fd == -1) {
+        const char *normalized_filename = bs->filename;
+        ret = raw_normalize_devicepath(&normalized_filename, errp);
+        if (ret >= 0) {
+            assert(!(*open_flags & O_CREAT));
+            fd = qemu_open(normalized_filename, *open_flags);
+            if (fd == -1) {
+                error_setg_errno(errp, errno, "Could not reopen file");
+                return -1;
+            }
+        }
+    }
+
+    return fd;
+}
+
 static int raw_reopen_prepare(BDRVReopenState *state,
                               BlockReopenQueue *queue, Error **errp)
 {
     BDRVRawState *s;
     BDRVRawReopenState *rs;
     QemuOpts *opts;
-    int ret = 0;
+    int ret;
     Error *local_err = NULL;
 
     assert(state != NULL);
@@ -858,7 +923,6 @@ static int raw_reopen_prepare(BDRVReopenState *state,
 
     state->opaque = g_new0(BDRVRawReopenState, 1);
     rs = state->opaque;
-    rs->fd = -1;
 
     /* Handle options changes */
     opts = qemu_opts_create(&raw_runtime_opts, NULL, 0, &error_abort);
@@ -877,50 +941,12 @@ static int raw_reopen_prepare(BDRVReopenState *state,
      * bdrv_reopen_prepare() will detect changes and complain. */
     qemu_opts_to_qdict(opts, state->options);
 
-    if (s->type == FTYPE_CD) {
-        rs->open_flags |= O_NONBLOCK;
-    }
-
-    raw_parse_flags(state->flags, &rs->open_flags);
-
-    int fcntl_flags = O_APPEND | O_NONBLOCK;
-#ifdef O_NOATIME
-    fcntl_flags |= O_NOATIME;
-#endif
-
-#ifdef O_ASYNC
-    /* Not all operating systems have O_ASYNC, and those that don't
-     * will not let us track the state into rs->open_flags (typically
-     * you achieve the same effect with an ioctl, for example I_SETSIG
-     * on Solaris). But we do not use O_ASYNC, so that's fine.
-     */
-    assert((s->open_flags & O_ASYNC) == 0);
-#endif
-
-    if ((rs->open_flags & ~fcntl_flags) == (s->open_flags & ~fcntl_flags)) {
-        /* dup the original fd */
-        rs->fd = qemu_dup(s->fd);
-        if (rs->fd >= 0) {
-            ret = fcntl_setfl(rs->fd, rs->open_flags);
-            if (ret) {
-                qemu_close(rs->fd);
-                rs->fd = -1;
-            }
-        }
-    }
-
-    /* If we cannot use fcntl, or fcntl failed, fall back to qemu_open() */
-    if (rs->fd == -1) {
-        const char *normalized_filename = state->bs->filename;
-        ret = raw_normalize_devicepath(&normalized_filename, errp);
-        if (ret >= 0) {
-            assert(!(rs->open_flags & O_CREAT));
-            rs->fd = qemu_open(normalized_filename, rs->open_flags);
-            if (rs->fd == -1) {
-                error_setg_errno(errp, errno, "Could not reopen file");
-                ret = -1;
-            }
-        }
+    rs->fd = raw_reconfigure_getfd(state->bs, state->flags, &rs->open_flags,
+                                   state->perm, true, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        ret = -1;
+        goto out;
     }
 
     /* Fail already reopen_prepare() if we can't get a working O_DIRECT
@@ -928,13 +954,19 @@ static int raw_reopen_prepare(BDRVReopenState *state,
     if (rs->fd != -1) {
         raw_probe_alignment(state->bs, rs->fd, &local_err);
         if (local_err) {
-            qemu_close(rs->fd);
-            rs->fd = -1;
             error_propagate(errp, local_err);
             ret = -EINVAL;
+            goto out_fd;
         }
     }
 
+    s->reopen_state = state;
+    ret = 0;
+out_fd:
+    if (ret < 0) {
+        qemu_close(rs->fd);
+        rs->fd = -1;
+    }
 out:
     qemu_opts_del(opts);
     return ret;
@@ -944,29 +976,25 @@ static void raw_reopen_commit(BDRVReopenState *state)
 {
     BDRVRawReopenState *rs = state->opaque;
     BDRVRawState *s = state->bs->opaque;
-    Error *local_err = NULL;
 
     s->check_cache_dropped = rs->check_cache_dropped;
     s->open_flags = rs->open_flags;
 
-    /* Copy locks to the new fd before closing the old one. */
-    raw_apply_lock_bytes(NULL, rs->fd, s->locked_perm,
-                         s->locked_shared_perm, false, &local_err);
-    if (local_err) {
-        /* shouldn't fail in a sane host, but report it just in case. */
-        error_report_err(local_err);
-    }
     qemu_close(s->fd);
     s->fd = rs->fd;
 
     g_free(state->opaque);
     state->opaque = NULL;
+
+    assert(s->reopen_state == state);
+    s->reopen_state = NULL;
 }
 
 
 static void raw_reopen_abort(BDRVReopenState *state)
 {
     BDRVRawReopenState *rs = state->opaque;
+    BDRVRawState *s = state->bs->opaque;
 
      /* nothing to do if NULL, we didn't get far enough */
     if (rs == NULL) {
@@ -979,6 +1007,9 @@ static void raw_reopen_abort(BDRVReopenState *state)
     }
     g_free(state->opaque);
     state->opaque = NULL;
+
+    assert(s->reopen_state == state);
+    s->reopen_state = NULL;
 }
 
 static int hdev_get_max_transfer_length(BlockDriverState *bs, int fd)
@@ -2664,12 +2695,78 @@ static QemuOptsList raw_create_opts = {
 static int raw_check_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared,
                           Error **errp)
 {
-    return raw_handle_perm_lock(bs, RAW_PL_PREPARE, perm, shared, errp);
+    BDRVRawState *s = bs->opaque;
+    BDRVRawReopenState *rs = NULL;
+    int open_flags;
+    int ret;
+
+    if (s->perm_change_fd) {
+        /*
+         * In the context of reopen, this function may be called several times
+         * (directly and recursively while change permissions of the parent).
+         * This is even true for children that don't inherit from the original
+         * reopen node, so s->reopen_state is not set.
+         *
+         * Ignore all but the first call.
+         */
+        return 0;
+    }
+
+    if (s->reopen_state) {
+        /* We already have a new file descriptor to set permissions for */
+        assert(s->reopen_state->perm == perm);
+        assert(s->reopen_state->shared_perm == shared);
+        rs = s->reopen_state->opaque;
+        s->perm_change_fd = rs->fd;
+    } else {
+        /* We may need a new fd if auto-read-only switches the mode */
+        ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags, perm,
+                                    false, errp);
+        if (ret < 0) {
+            return ret;
+        } else if (ret != s->fd) {
+            s->perm_change_fd = ret;
+        }
+    }
+
+    /* Prepare permissions on old fd to avoid conflicts between old and new,
+     * but keep everything locked that new will need. */
+    ret = raw_handle_perm_lock(bs, RAW_PL_PREPARE, perm, shared, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /* Copy locks to the new fd */
+    if (s->perm_change_fd) {
+        ret = raw_apply_lock_bytes(NULL, s->perm_change_fd, perm, ~shared,
+                                   false, errp);
+        if (ret < 0) {
+            raw_handle_perm_lock(bs, RAW_PL_ABORT, 0, 0, NULL);
+            goto fail;
+        }
+    }
+    return 0;
+
+fail:
+    if (s->perm_change_fd && !s->reopen_state) {
+        qemu_close(s->perm_change_fd);
+    }
+    s->perm_change_fd = 0;
+    return ret;
 }
 
 static void raw_set_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared)
 {
     BDRVRawState *s = bs->opaque;
+
+    /* For reopen, we have already switched to the new fd (.bdrv_set_perm is
+     * called after .bdrv_reopen_commit) */
+    if (s->perm_change_fd && s->fd != s->perm_change_fd) {
+        qemu_close(s->fd);
+        s->fd = s->perm_change_fd;
+    }
+    s->perm_change_fd = 0;
+
     raw_handle_perm_lock(bs, RAW_PL_COMMIT, perm, shared, NULL);
     s->perm = perm;
     s->shared_perm = shared;
@@ -2677,6 +2774,15 @@ static void raw_set_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared)
 
 static void raw_abort_perm_update(BlockDriverState *bs)
 {
+    BDRVRawState *s = bs->opaque;
+
+    /* For reopen, .bdrv_reopen_abort is called afterwards and will close
+     * the file descriptor. */
+    if (s->perm_change_fd && !s->reopen_state) {
+        qemu_close(s->perm_change_fd);
+    }
+    s->perm_change_fd = 0;
+
     raw_handle_perm_lock(bs, RAW_PL_ABORT, 0, 0, NULL);
 }
 
@@ -2766,6 +2872,7 @@ BlockDriver bdrv_file = {
     .bdrv_set_perm   = raw_set_perm,
     .bdrv_abort_perm_update = raw_abort_perm_update,
     .create_opts = &raw_create_opts,
+    .mutable_opts = mutable_opts,
 };
 
 /***********************************************/
@@ -3217,6 +3324,7 @@ static BlockDriver bdrv_host_device = {
     .bdrv_reopen_abort   = raw_reopen_abort,
     .bdrv_co_create_opts = hdev_co_create_opts,
     .create_opts         = &raw_create_opts,
+    .mutable_opts        = mutable_opts,
     .bdrv_co_invalidate_cache = raw_co_invalidate_cache,
     .bdrv_co_pwrite_zeroes = hdev_co_pwrite_zeroes,
 
@@ -3343,6 +3451,7 @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_reopen_abort   = raw_reopen_abort,
     .bdrv_co_create_opts = hdev_co_create_opts,
     .create_opts         = &raw_create_opts,
+    .mutable_opts        = mutable_opts,
     .bdrv_co_invalidate_cache = raw_co_invalidate_cache,
 
 
@@ -3476,6 +3585,7 @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_reopen_abort   = raw_reopen_abort,
     .bdrv_co_create_opts = hdev_co_create_opts,
     .create_opts        = &raw_create_opts,
+    .mutable_opts       = mutable_opts,
 
     .bdrv_co_preadv         = raw_co_preadv,
     .bdrv_co_pwritev        = raw_co_pwritev,
diff --git a/block/gluster.c b/block/gluster.c
index af64330211..51f184cbd8 100644
--- a/block/gluster.c
+++ b/block/gluster.c
@@ -20,6 +20,10 @@
 #include "qemu/option.h"
 #include "qemu/cutils.h"
 
+#ifdef CONFIG_GLUSTERFS_FTRUNCATE_HAS_STAT
+# define glfs_ftruncate(fd, offset) glfs_ftruncate(fd, offset, NULL, NULL)
+#endif
+
 #define GLUSTER_OPT_FILENAME        "filename"
 #define GLUSTER_OPT_VOLUME          "volume"
 #define GLUSTER_OPT_PATH            "path"
@@ -725,7 +729,11 @@ static struct glfs *qemu_gluster_init(BlockdevOptionsGluster *gconf,
 /*
  * AIO callback routine called from GlusterFS thread.
  */
-static void gluster_finish_aiocb(struct glfs_fd *fd, ssize_t ret, void *arg)
+static void gluster_finish_aiocb(struct glfs_fd *fd, ssize_t ret,
+#ifdef CONFIG_GLUSTERFS_IOCB_HAS_STAT
+                                 struct glfs_stat *pre, struct glfs_stat *post,
+#endif
+                                 void *arg)
 {
     GlusterAIOCB *acb = (GlusterAIOCB *)arg;
 
diff --git a/block/mirror.c b/block/mirror.c
index 726d3c27fb..010fdafd79 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -630,6 +630,10 @@ static int mirror_exit_common(Job *job)
     }
     s->prepared = true;
 
+    if (bdrv_chain_contains(src, target_bs)) {
+        bdrv_unfreeze_backing_chain(mirror_top_bs, target_bs);
+    }
+
     bdrv_release_dirty_bitmap(src, s->dirty_bitmap);
 
     /* Make sure that the source BDS doesn't go away during bdrv_replace_node,
@@ -1639,6 +1643,10 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
                 goto fail;
             }
         }
+
+        if (bdrv_freeze_backing_chain(mirror_top_bs, target, errp) < 0) {
+            goto fail;
+        }
     }
 
     QTAILQ_INIT(&s->ops_in_flight);
diff --git a/block/qapi.c b/block/qapi.c
index 6002a768f8..21edab34fc 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -493,14 +493,14 @@ static void bdrv_query_blk_stats(BlockDeviceStats *ds, BlockBackend *blk)
     }
 
     bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_READ],
-                                 &ds->has_x_rd_latency_histogram,
-                                 &ds->x_rd_latency_histogram);
+                                 &ds->has_rd_latency_histogram,
+                                 &ds->rd_latency_histogram);
     bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_WRITE],
-                                 &ds->has_x_wr_latency_histogram,
-                                 &ds->x_wr_latency_histogram);
+                                 &ds->has_wr_latency_histogram,
+                                 &ds->wr_latency_histogram);
     bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_FLUSH],
-                                 &ds->has_x_flush_latency_histogram,
-                                 &ds->x_flush_latency_histogram);
+                                 &ds->has_flush_latency_histogram,
+                                 &ds->flush_latency_histogram);
 }
 
 static BlockStats *bdrv_query_bds_stats(BlockDriverState *bs,
diff --git a/block/qcow2.c b/block/qcow2.c
index c4dd876fb4..0fc9b0561e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -627,6 +627,30 @@ int qcow2_validate_table(BlockDriverState *bs, uint64_t offset,
     return 0;
 }
 
+static const char *const mutable_opts[] = {
+    QCOW2_OPT_LAZY_REFCOUNTS,
+    QCOW2_OPT_DISCARD_REQUEST,
+    QCOW2_OPT_DISCARD_SNAPSHOT,
+    QCOW2_OPT_DISCARD_OTHER,
+    QCOW2_OPT_OVERLAP,
+    QCOW2_OPT_OVERLAP_TEMPLATE,
+    QCOW2_OPT_OVERLAP_MAIN_HEADER,
+    QCOW2_OPT_OVERLAP_ACTIVE_L1,
+    QCOW2_OPT_OVERLAP_ACTIVE_L2,
+    QCOW2_OPT_OVERLAP_REFCOUNT_TABLE,
+    QCOW2_OPT_OVERLAP_REFCOUNT_BLOCK,
+    QCOW2_OPT_OVERLAP_SNAPSHOT_TABLE,
+    QCOW2_OPT_OVERLAP_INACTIVE_L1,
+    QCOW2_OPT_OVERLAP_INACTIVE_L2,
+    QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY,
+    QCOW2_OPT_CACHE_SIZE,
+    QCOW2_OPT_L2_CACHE_SIZE,
+    QCOW2_OPT_L2_CACHE_ENTRY_SIZE,
+    QCOW2_OPT_REFCOUNT_CACHE_SIZE,
+    QCOW2_OPT_CACHE_CLEAN_INTERVAL,
+    NULL
+};
+
 static QemuOptsList qcow2_runtime_opts = {
     .name = "qcow2",
     .head = QTAILQ_HEAD_INITIALIZER(qcow2_runtime_opts.head),
@@ -5275,6 +5299,7 @@ BlockDriver bdrv_qcow2 = {
 
     .create_opts         = &qcow2_create_opts,
     .strong_runtime_opts = qcow2_strong_runtime_opts,
+    .mutable_opts        = mutable_opts,
     .bdrv_co_check       = qcow2_co_check,
     .bdrv_amend_options  = qcow2_amend_options,
 
diff --git a/block/raw-format.c b/block/raw-format.c
index e3e5ba2c8a..cec29986cc 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -37,6 +37,8 @@ typedef struct BDRVRawState {
     bool has_size;
 } BDRVRawState;
 
+static const char *const mutable_opts[] = { "offset", "size", NULL };
+
 static QemuOptsList raw_runtime_opts = {
     .name = "raw",
     .head = QTAILQ_HEAD_INITIALIZER(raw_runtime_opts.head),
@@ -570,6 +572,7 @@ BlockDriver bdrv_raw = {
     .create_opts          = &raw_create_opts,
     .bdrv_has_zero_init   = &raw_has_zero_init,
     .strong_runtime_opts  = raw_strong_runtime_opts,
+    .mutable_opts         = mutable_opts,
 };
 
 static void bdrv_raw_init(void)
diff --git a/block/replication.c b/block/replication.c
index 4c80b54daf..b95bd28802 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -374,19 +374,18 @@ static void reopen_backing_file(BlockDriverState *bs, bool writable,
         QDict *opts = qdict_new();
         qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
         reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs,
-                                         opts);
+                                         opts, true);
     }
 
     if (s->orig_secondary_read_only) {
         QDict *opts = qdict_new();
         qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
         reopen_queue = bdrv_reopen_queue(reopen_queue, s->secondary_disk->bs,
-                                         opts);
+                                         opts, true);
     }
 
     if (reopen_queue) {
-        bdrv_reopen_multiple(bdrv_get_aio_context(bs),
-                             reopen_queue, &local_err);
+        bdrv_reopen_multiple(reopen_queue, &local_err);
         error_propagate(errp, local_err);
     }
 
diff --git a/block/stream.c b/block/stream.c
index e14579ff80..6253c86fae 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -35,6 +35,7 @@ typedef struct StreamBlockJob {
     BlockdevOnError on_error;
     char *backing_file_str;
     bool bs_read_only;
+    bool chain_frozen;
 } StreamBlockJob;
 
 static int coroutine_fn stream_populate(BlockBackend *blk,
@@ -49,6 +50,16 @@ static int coroutine_fn stream_populate(BlockBackend *blk,
     return blk_co_preadv(blk, offset, qiov.size, &qiov, BDRV_REQ_COPY_ON_READ);
 }
 
+static void stream_abort(Job *job)
+{
+    StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
+
+    if (s->chain_frozen) {
+        BlockJob *bjob = &s->common;
+        bdrv_unfreeze_backing_chain(blk_bs(bjob->blk), s->base);
+    }
+}
+
 static int stream_prepare(Job *job)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
@@ -58,6 +69,9 @@ static int stream_prepare(Job *job)
     Error *local_err = NULL;
     int ret = 0;
 
+    bdrv_unfreeze_backing_chain(bs, base);
+    s->chain_frozen = false;
+
     if (bs->backing) {
         const char *base_id = NULL, *base_fmt = NULL;
         if (base) {
@@ -208,6 +222,7 @@ static const BlockJobDriver stream_job_driver = {
         .free          = block_job_free,
         .run           = stream_run,
         .prepare       = stream_prepare,
+        .abort         = stream_abort,
         .clean         = stream_clean,
         .user_resume   = block_job_user_resume,
         .drain         = block_job_drain,
@@ -254,9 +269,15 @@ void stream_start(const char *job_id, BlockDriverState *bs,
                            &error_abort);
     }
 
+    if (bdrv_freeze_backing_chain(bs, base, errp) < 0) {
+        job_early_fail(&s->common.job);
+        goto fail;
+    }
+
     s->base = base;
     s->backing_file_str = g_strdup(backing_file_str);
     s->bs_read_only = bs_read_only;
+    s->chain_frozen = true;
 
     s->on_error = on_error;
     trace_stream_start(bs, base, s);
diff --git a/blockdev.c b/blockdev.c
index 871966ca13..3cc51b2ee7 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -4287,6 +4287,53 @@ fail:
     visit_free(v);
 }
 
+void qmp_x_blockdev_reopen(BlockdevOptions *options, Error **errp)
+{
+    BlockDriverState *bs;
+    AioContext *ctx;
+    QObject *obj;
+    Visitor *v = qobject_output_visitor_new(&obj);
+    Error *local_err = NULL;
+    BlockReopenQueue *queue;
+    QDict *qdict;
+
+    /* Check for the selected node name */
+    if (!options->has_node_name) {
+        error_setg(errp, "Node name not specified");
+        goto fail;
+    }
+
+    bs = bdrv_find_node(options->node_name);
+    if (!bs) {
+        error_setg(errp, "Cannot find node named '%s'", options->node_name);
+        goto fail;
+    }
+
+    /* Put all options in a QDict and flatten it */
+    visit_type_BlockdevOptions(v, NULL, &options, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        goto fail;
+    }
+
+    visit_complete(v, &obj);
+    qdict = qobject_to(QDict, obj);
+
+    qdict_flatten(qdict);
+
+    /* Perform the reopen operation */
+    ctx = bdrv_get_aio_context(bs);
+    aio_context_acquire(ctx);
+    bdrv_subtree_drained_begin(bs);
+    queue = bdrv_reopen_queue(NULL, bs, qdict, false);
+    bdrv_reopen_multiple(queue, errp);
+    bdrv_subtree_drained_end(bs);
+    aio_context_release(ctx);
+
+fail:
+    visit_free(v);
+}
+
 void qmp_blockdev_del(const char *node_name, Error **errp)
 {
     AioContext *aio_context;
@@ -4452,22 +4499,22 @@ void qmp_x_blockdev_set_iothread(const char *node_name, StrOrNull *iothread,
     aio_context_release(old_context);
 }
 
-void qmp_x_block_latency_histogram_set(
-    const char *device,
+void qmp_block_latency_histogram_set(
+    const char *id,
     bool has_boundaries, uint64List *boundaries,
     bool has_boundaries_read, uint64List *boundaries_read,
     bool has_boundaries_write, uint64List *boundaries_write,
     bool has_boundaries_flush, uint64List *boundaries_flush,
     Error **errp)
 {
-    BlockBackend *blk = blk_by_name(device);
+    BlockBackend *blk = qmp_get_blk(NULL, id, errp);
     BlockAcctStats *stats;
     int ret;
 
     if (!blk) {
-        error_setg(errp, "Device '%s' not found", device);
         return;
     }
+
     stats = blk_get_stats(blk);
 
     if (!has_boundaries && !has_boundaries_read && !has_boundaries_write &&
@@ -4482,7 +4529,7 @@ void qmp_x_block_latency_histogram_set(
             stats, BLOCK_ACCT_READ,
             has_boundaries_read ? boundaries_read : boundaries);
         if (ret) {
-            error_setg(errp, "Device '%s' set read boundaries fail", device);
+            error_setg(errp, "Device '%s' set read boundaries fail", id);
             return;
         }
     }
@@ -4492,7 +4539,7 @@ void qmp_x_block_latency_histogram_set(
             stats, BLOCK_ACCT_WRITE,
             has_boundaries_write ? boundaries_write : boundaries);
         if (ret) {
-            error_setg(errp, "Device '%s' set write boundaries fail", device);
+            error_setg(errp, "Device '%s' set write boundaries fail", id);
             return;
         }
     }
@@ -4502,7 +4549,7 @@ void qmp_x_block_latency_histogram_set(
             stats, BLOCK_ACCT_FLUSH,
             has_boundaries_flush ? boundaries_flush : boundaries);
         if (ret) {
-            error_setg(errp, "Device '%s' set flush boundaries fail", device);
+            error_setg(errp, "Device '%s' set flush boundaries fail", id);
             return;
         }
     }
diff --git a/configure b/configure
index cab830a4c9..45a3654c5b 100755
--- a/configure
+++ b/configure
@@ -456,6 +456,8 @@ glusterfs_xlator_opt="no"
 glusterfs_discard="no"
 glusterfs_fallocate="no"
 glusterfs_zerofill="no"
+glusterfs_ftruncate_has_stat="no"
+glusterfs_iocb_has_stat="no"
 gtk=""
 gtk_gl="no"
 tls_priority="NORMAL"
@@ -4091,6 +4093,38 @@ if test "$glusterfs" != "no" ; then
       glusterfs_fallocate="yes"
       glusterfs_zerofill="yes"
     fi
+    cat > $TMPC << EOF
+#include <glusterfs/api/glfs.h>
+
+int
+main(void)
+{
+	/* new glfs_ftruncate() passes two additional args */
+	return glfs_ftruncate(NULL, 0, NULL, NULL);
+}
+EOF
+    if compile_prog "$glusterfs_cflags" "$glusterfs_libs" ; then
+      glusterfs_ftruncate_has_stat="yes"
+    fi
+    cat > $TMPC << EOF
+#include <glusterfs/api/glfs.h>
+
+/* new glfs_io_cbk() passes two additional glfs_stat structs */
+static void
+glusterfs_iocb(glfs_fd_t *fd, ssize_t ret, struct glfs_stat *prestat, struct glfs_stat *poststat, void *data)
+{}
+
+int
+main(void)
+{
+	glfs_io_cbk iocb = &glusterfs_iocb;
+	iocb(NULL, 0 , NULL, NULL, NULL);
+	return 0;
+}
+EOF
+    if compile_prog "$glusterfs_cflags" "$glusterfs_libs" ; then
+      glusterfs_iocb_has_stat="yes"
+    fi
   else
     if test "$glusterfs" = "yes" ; then
       feature_not_found "GlusterFS backend support" \
@@ -6976,6 +7010,14 @@ if test "$glusterfs_zerofill" = "yes" ; then
   echo "CONFIG_GLUSTERFS_ZEROFILL=y" >> $config_host_mak
 fi
 
+if test "$glusterfs_ftruncate_has_stat" = "yes" ; then
+  echo "CONFIG_GLUSTERFS_FTRUNCATE_HAS_STAT=y" >> $config_host_mak
+fi
+
+if test "$glusterfs_iocb_has_stat" = "yes" ; then
+  echo "CONFIG_GLUSTERFS_IOCB_HAS_STAT=y" >> $config_host_mak
+fi
+
 if test "$libssh2" = "yes" ; then
   echo "CONFIG_LIBSSH2=m" >> $config_host_mak
   echo "LIBSSH2_CFLAGS=$libssh2_cflags" >> $config_host_mak
diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 8325b5e88a..7caf92532a 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -324,8 +324,8 @@ static uint16_t nvme_write_zeros(NvmeCtrl *n, NvmeNamespace *ns, NvmeCmd *cmd,
     const uint8_t data_shift = ns->id_ns.lbaf[lba_index].ds;
     uint64_t slba = le64_to_cpu(rw->slba);
     uint32_t nlb  = le16_to_cpu(rw->nlb) + 1;
-    uint64_t aio_slba = slba << (data_shift - BDRV_SECTOR_BITS);
-    uint32_t aio_nlb = nlb << (data_shift - BDRV_SECTOR_BITS);
+    uint64_t offset = slba << data_shift;
+    uint32_t count = nlb << data_shift;
 
     if (unlikely(slba + nlb > ns->id_ns.nsze)) {
         trace_nvme_err_invalid_lba_range(slba, nlb, ns->id_ns.nsze);
@@ -335,7 +335,7 @@ static uint16_t nvme_write_zeros(NvmeCtrl *n, NvmeNamespace *ns, NvmeCmd *cmd,
     req->has_sg = false;
     block_acct_start(blk_get_stats(n->conf.blk), &req->acct, 0,
                      BLOCK_ACCT_WRITE);
-    req->aiocb = blk_aio_pwrite_zeroes(n->conf.blk, aio_slba, aio_nlb,
+    req->aiocb = blk_aio_pwrite_zeroes(n->conf.blk, offset, count,
                                         BDRV_REQ_MAY_UNMAP, nvme_rw_cb, req);
     return NVME_NO_COMPLETE;
 }
diff --git a/include/block/block.h b/include/block/block.h
index 6a758a76f8..e452988b66 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -187,6 +187,9 @@ typedef struct BDRVReopenState {
     BlockDriverState *bs;
     int flags;
     BlockdevDetectZeroesOptions detect_zeroes;
+    bool backing_missing;
+    bool replace_backing_bs;  /* new_backing_bs is ignored if this is false */
+    BlockDriverState *new_backing_bs; /* If NULL then detach the current bs */
     uint64_t perm, shared_perm;
     QDict *options;
     QDict *explicit_options;
@@ -299,8 +302,9 @@ BlockDriverState *bdrv_open(const char *filename, const char *reference,
 BlockDriverState *bdrv_new_open_driver(BlockDriver *drv, const char *node_name,
                                        int flags, Error **errp);
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
-                                    BlockDriverState *bs, QDict *options);
-int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **errp);
+                                    BlockDriverState *bs, QDict *options,
+                                    bool keep_old_opts);
+int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp);
 int bdrv_reopen_set_read_only(BlockDriverState *bs, bool read_only,
                               Error **errp);
 int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
@@ -353,6 +357,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs);
 BlockDriverState *bdrv_find_base(BlockDriverState *bs);
+bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+                                  Error **errp);
+int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
+                              Error **errp);
+void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base);
 
 
 typedef struct BdrvCheckResult {
diff --git a/include/block/block_int.h b/include/block/block_int.h
index a23cabaddd..01e855a066 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -383,6 +383,14 @@ struct BlockDriver {
 
     /* List of options for creating images, terminated by name == NULL */
     QemuOptsList *create_opts;
+    /*
+     * If this driver supports reopening images this contains a
+     * NULL-terminated list of the runtime options that can be
+     * modified. If an option in this list is unspecified during
+     * reopen then it _must_ be reset to its default value or return
+     * an error.
+     */
+    const char *const *mutable_opts;
 
     /*
      * Returns 0 for completed check, -errno for internal errors.
@@ -711,6 +719,12 @@ struct BdrvChild {
     uint64_t backup_perm;
     uint64_t backup_shared_perm;
 
+    /*
+     * This link is frozen: the child can neither be replaced nor
+     * detached from the parent.
+     */
+    bool frozen;
+
     QLIST_ENTRY(BdrvChild) next;
     QLIST_ENTRY(BdrvChild) next_parent;
 };
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 919d0530b2..474e268c4d 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -537,20 +537,20 @@
 #         +------------------
 #             10   50   100
 #
-# Since: 2.12
+# Since: 4.0
 ##
 { 'struct': 'BlockLatencyHistogramInfo',
   'data': {'boundaries': ['uint64'], 'bins': ['uint64'] } }
 
 ##
-# @x-block-latency-histogram-set:
+# @block-latency-histogram-set:
 #
 # Manage read, write and flush latency histograms for the device.
 #
 # If only @device parameter is specified, remove all present latency histograms
 # for the device. Otherwise, add/reset some of (or all) latency histograms.
 #
-# @device: device name to set latency histogram for.
+# @id: The name or QOM path of the guest device.
 #
 # @boundaries: list of interval boundary values (see description in
 #              BlockLatencyHistogramInfo definition). If specified, all
@@ -573,7 +573,7 @@
 #
 # Returns: error if device is not found or any boundary arrays are invalid.
 #
-# Since: 2.12
+# Since: 4.0
 #
 # Example: set new histograms for all io types with intervals
 # [0, 10), [10, 50), [50, 100), [100, +inf):
@@ -607,8 +607,8 @@
 #      "arguments": { "device": "drive0" } }
 # <- { "return": {} }
 ##
-{ 'command': 'x-block-latency-histogram-set',
-  'data': {'device': 'str',
+{ 'command': 'block-latency-histogram-set',
+  'data': {'id': 'str',
            '*boundaries': ['uint64'],
            '*boundaries-read': ['uint64'],
            '*boundaries-write': ['uint64'],
@@ -894,11 +894,11 @@
 # @timed_stats: Statistics specific to the set of previously defined
 #               intervals of time (Since 2.5)
 #
-# @x_rd_latency_histogram: @BlockLatencyHistogramInfo. (Since 2.12)
+# @rd_latency_histogram: @BlockLatencyHistogramInfo. (Since 4.0)
 #
-# @x_wr_latency_histogram: @BlockLatencyHistogramInfo. (Since 2.12)
+# @wr_latency_histogram: @BlockLatencyHistogramInfo. (Since 4.0)
 #
-# @x_flush_latency_histogram: @BlockLatencyHistogramInfo. (Since 2.12)
+# @flush_latency_histogram: @BlockLatencyHistogramInfo. (Since 4.0)
 #
 # Since: 0.14.0
 ##
@@ -913,9 +913,9 @@
            'invalid_wr_operations': 'int', 'invalid_flush_operations': 'int',
            'account_invalid': 'bool', 'account_failed': 'bool',
            'timed_stats': ['BlockDeviceTimedStats'],
-           '*x_rd_latency_histogram': 'BlockLatencyHistogramInfo',
-           '*x_wr_latency_histogram': 'BlockLatencyHistogramInfo',
-           '*x_flush_latency_histogram': 'BlockLatencyHistogramInfo' } }
+           '*rd_latency_histogram': 'BlockLatencyHistogramInfo',
+           '*wr_latency_histogram': 'BlockLatencyHistogramInfo',
+           '*flush_latency_histogram': 'BlockLatencyHistogramInfo' } }
 
 ##
 # @BlockStats:
@@ -3998,6 +3998,48 @@
 { 'command': 'blockdev-add', 'data': 'BlockdevOptions', 'boxed': true }
 
 ##
+# @x-blockdev-reopen:
+#
+# Reopens a block device using the given set of options. Any option
+# not specified will be reset to its default value regardless of its
+# previous status. If an option cannot be changed or a particular
+# driver does not support reopening then the command will return an
+# error.
+#
+# The top-level @node-name option (from BlockdevOptions) must be
+# specified and is used to select the block device to be reopened.
+# Other @node-name options must be either omitted or set to the
+# current name of the appropriate node. This command won't change any
+# node name and any attempt to do it will result in an error.
+#
+# In the case of options that refer to child nodes, the behavior of
+# this command depends on the value:
+#
+#  1) A set of options (BlockdevOptions): the child is reopened with
+#     the specified set of options.
+#
+#  2) A reference to the current child: the child is reopened using
+#     its existing set of options.
+#
+#  3) A reference to a different node: the current child is replaced
+#     with the specified one.
+#
+#  4) NULL: the current child (if any) is detached.
+#
+# Options (1) and (2) are supported in all cases, but at the moment
+# only @backing allows replacing or detaching an existing child.
+#
+# Unlike with blockdev-add, the @backing option must always be present
+# unless the node being reopened does not have a backing file and its
+# image does not have a default backing file name as part of its
+# metadata.
+#
+# Since: 4.0
+##
+{ 'command': 'x-blockdev-reopen',
+  'data': 'BlockdevOptions', 'boxed': true }
+
+##
 # @blockdev-del:
 #
 # Deletes a block device that has been added using blockdev-add.
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index b9f189f09b..35dcdcf413 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -2080,8 +2080,8 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
     }
 
     bdrv_subtree_drained_begin(bs);
-    brq = bdrv_reopen_queue(NULL, bs, opts);
-    bdrv_reopen_multiple(bdrv_get_aio_context(bs), brq, &local_err);
+    brq = bdrv_reopen_queue(NULL, bs, opts, true);
+    bdrv_reopen_multiple(brq, &local_err);
     bdrv_subtree_drained_end(bs);
 
     if (local_err) {
diff --git a/tests/qemu-iotests/051 b/tests/qemu-iotests/051
index 3b50c7f188..6a3b7c2b89 100755
--- a/tests/qemu-iotests/051
+++ b/tests/qemu-iotests/051
@@ -356,6 +356,13 @@ $QEMU_IO -c "read -P 0x33 0 4k" "$TEST_IMG" | _filter_qemu_io
 # Using snapshot=on with a non-existent TMPDIR
 TMPDIR=/nonexistent run_qemu -drive driver=null-co,snapshot=on
 
+# Using snapshot=on together with read-only=on
+echo "info block" |
+    run_qemu -drive file="$TEST_IMG",snapshot=on,read-only=on,if=none,id=$device_id |
+    _filter_qemu_io |
+    sed -e 's#"/[^"]*/vl\.[A-Za-z0-9]\{6\}"#SNAPSHOT_PATH#g'
+
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/051.out b/tests/qemu-iotests/051.out
index b900935fbc..9f1cf22608 100644
--- a/tests/qemu-iotests/051.out
+++ b/tests/qemu-iotests/051.out
@@ -458,4 +458,13 @@ read 4096/4096 bytes at offset 0
 Testing: -drive driver=null-co,snapshot=on
 QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
 
+Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
+QEMU X.Y.Z monitor - type 'help' for more information
+(qemu) info block
+drive0 (NODE_NAME): json:{"backing": {"driver": "qcow2", "file": {"driver": "file", "filename": "TEST_DIR/t.qcow2"}}, "driver": "qcow2", "file": {"driver": "file", "filename": SNAPSHOT_PATH}} (qcow2, read-only)
+    Removable device: not locked, tray closed
+    Cache mode:       writeback, ignore flushes
+    Backing file:     TEST_DIR/t.qcow2 (chain depth: 1)
+(qemu) quit
+
 *** done
diff --git a/tests/qemu-iotests/051.pc.out b/tests/qemu-iotests/051.pc.out
index 8c5c735dfd..c4743cc31c 100644
--- a/tests/qemu-iotests/051.pc.out
+++ b/tests/qemu-iotests/051.pc.out
@@ -530,4 +530,13 @@ read 4096/4096 bytes at offset 0
 Testing: -drive driver=null-co,snapshot=on
 QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
 
+Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
+QEMU X.Y.Z monitor - type 'help' for more information
+(qemu) info block
+drive0 (NODE_NAME): json:{"backing": {"driver": "qcow2", "file": {"driver": "file", "filename": "TEST_DIR/t.qcow2"}}, "driver": "qcow2", "file": {"driver": "file", "filename": SNAPSHOT_PATH}} (qcow2, read-only)
+    Removable device: not locked, tray closed
+    Cache mode:       writeback, ignore flushes
+    Backing file:     TEST_DIR/t.qcow2 (chain depth: 1)
+(qemu) quit
+
 *** done
diff --git a/tests/qemu-iotests/232 b/tests/qemu-iotests/232
index 71fd48eff0..0de097fc88 100755
--- a/tests/qemu-iotests/232
+++ b/tests/qemu-iotests/232
@@ -29,6 +29,7 @@ status=1	# failure is the default!
 _cleanup()
 {
     _cleanup_test_img
+    rm -f $TEST_IMG.[01234]
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15
 
@@ -143,6 +144,36 @@ run_qemu_info_block -blockdev driver=file,filename="$TEST_IMG",node-name=node0,a
 run_qemu_info_block -blockdev driver=file,filename="$TEST_IMG",node-name=node0,auto-read-only=on
 run_qemu_info_block -blockdev driver=file,filename="$TEST_IMG",node-name=node0
 
+echo
+echo "=== Try commit to backing file with auto-read-only ==="
+echo
+
+TEST_IMG="$TEST_IMG.0" _make_test_img $size
+TEST_IMG="$TEST_IMG.1" _make_test_img $size
+TEST_IMG="$TEST_IMG.2" _make_test_img $size
+TEST_IMG="$TEST_IMG.3" _make_test_img $size
+TEST_IMG="$TEST_IMG.4" _make_test_img $size
+
+(cat <<EOF
+{"execute":"qmp_capabilities"}
+{"execute":"block-commit",
+ "arguments":{"device":"format-4", "top-node": "format-2", "base-node":"format-0", "job-id":"job0"}}
+EOF
+sleep 1
+echo '{"execute":"quit"}'
+) | $QEMU -qmp stdio -nographic -nodefaults \
+    -blockdev file,node-name=file-0,filename=$TEST_IMG.0,auto-read-only=on \
+    -blockdev qcow2,node-name=format-0,file=file-0,read-only=on \
+    -blockdev file,node-name=file-1,filename=$TEST_IMG.1,auto-read-only=on \
+    -blockdev qcow2,node-name=format-1,file=file-1,read-only=on,backing=format-0 \
+    -blockdev file,node-name=file-2,filename=$TEST_IMG.2,auto-read-only=on \
+    -blockdev qcow2,node-name=format-2,file=file-2,read-only=on,backing=format-1 \
+    -blockdev file,node-name=file-3,filename=$TEST_IMG.3,auto-read-only=on \
+    -blockdev qcow2,node-name=format-3,file=file-3,read-only=on,backing=format-2 \
+    -blockdev file,node-name=file-4,filename=$TEST_IMG.4,auto-read-only=on \
+    -blockdev qcow2,node-name=format-4,file=file-4,read-only=on,backing=format-3 |
+    _filter_qmp
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/232.out b/tests/qemu-iotests/232.out
index dcb683afa3..5bcc44bb62 100644
--- a/tests/qemu-iotests/232.out
+++ b/tests/qemu-iotests/232.out
@@ -22,12 +22,12 @@ NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
 NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
 
 QEMU_PROG: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=none,read-only=off,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
-NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
-NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
+NODE_NAME: TEST_DIR/t.IMGFMT (file)
+NODE_NAME: TEST_DIR/t.IMGFMT (file)
 
 QEMU_PROG: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=none,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
-NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
-NODE_NAME: TEST_DIR/t.IMGFMT (file, read-only)
+NODE_NAME: TEST_DIR/t.IMGFMT (file)
+NODE_NAME: TEST_DIR/t.IMGFMT (file)
 
 === -blockdev with read-write image: read-only/auto-read-only combinations ===
 
@@ -50,10 +50,30 @@ node0: TEST_DIR/t.IMGFMT (file, read-only)
 node0: TEST_DIR/t.IMGFMT (file, read-only)
 
 QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,read-only=off,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
-node0: TEST_DIR/t.IMGFMT (file, read-only)
+node0: TEST_DIR/t.IMGFMT (file)
 QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
 
 QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0,auto-read-only=off: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
-node0: TEST_DIR/t.IMGFMT (file, read-only)
+node0: TEST_DIR/t.IMGFMT (file)
 QEMU_PROG: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=node0: Could not open 'TEST_DIR/t.IMGFMT': Permission denied
+
+=== Try commit to backing file with auto-read-only ===
+
+Formatting 'TEST_DIR/t.IMGFMT.0', fmt=IMGFMT size=134217728
+Formatting 'TEST_DIR/t.IMGFMT.1', fmt=IMGFMT size=134217728
+Formatting 'TEST_DIR/t.IMGFMT.2', fmt=IMGFMT size=134217728
+Formatting 'TEST_DIR/t.IMGFMT.3', fmt=IMGFMT size=134217728
+Formatting 'TEST_DIR/t.IMGFMT.4', fmt=IMGFMT size=134217728
+QMP_VERSION
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "created", "id": "job0"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "waiting", "id": "job0"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "pending", "id": "job0"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_JOB_COMPLETED", "data": {"device": "job0", "len": 134217728, "offset": 134217728, "speed": 0, "type": "commit"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "concluded", "id": "job0"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "null", "id": "job0"}}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
 *** done
diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
new file mode 100644
index 0000000000..7891a210c1
--- /dev/null
+++ b/tests/qemu-iotests/245
@@ -0,0 +1,991 @@
+#!/usr/bin/env python
+#
+# Test cases for the QMP 'x-blockdev-reopen' command
+#
+# Copyright (C) 2018-2019 Igalia, S.L.
+# Author: Alberto Garcia <berto@igalia.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+import os
+import re
+import iotests
+import copy
+import json
+from iotests import qemu_img, qemu_io
+
+hd_path = [
+    os.path.join(iotests.test_dir, 'hd0.img'),
+    os.path.join(iotests.test_dir, 'hd1.img'),
+    os.path.join(iotests.test_dir, 'hd2.img')
+]
+
+def hd_opts(idx):
+    return {'driver': iotests.imgfmt,
+            'node-name': 'hd%d' % idx,
+            'file': {'driver': 'file',
+                     'node-name': 'hd%d-file' % idx,
+                     'filename':  hd_path[idx] } }
+
+class TestBlockdevReopen(iotests.QMPTestCase):
+    total_io_cmds = 0
+
+    def setUp(self):
+        qemu_img('create', '-f', iotests.imgfmt, hd_path[0], '3M')
+        qemu_img('create', '-f', iotests.imgfmt, '-b', hd_path[0], hd_path[1])
+        qemu_img('create', '-f', iotests.imgfmt, hd_path[2], '3M')
+        qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xa0  0 1M', hd_path[0])
+        qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xa1 1M 1M', hd_path[1])
+        qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xa2 2M 1M', hd_path[2])
+        self.vm = iotests.VM()
+        self.vm.launch()
+
+    def tearDown(self):
+        self.vm.shutdown()
+        self.check_qemu_io_errors()
+        os.remove(hd_path[0])
+        os.remove(hd_path[1])
+        os.remove(hd_path[2])
+
+    # The output of qemu-io is not returned by vm.hmp_qemu_io() but
+    # it's stored in the log and can only be read when the VM has been
+    # shut down. This function runs qemu-io and keeps track of the
+    # number of times it's been called.
+    def run_qemu_io(self, img, cmd):
+        result = self.vm.hmp_qemu_io(img, cmd)
+        self.assert_qmp(result, 'return', '')
+        self.total_io_cmds += 1
+
+    # Once the VM is shut down we can parse the log and see if qemu-io
+    # ran without errors.
+    def check_qemu_io_errors(self):
+        self.assertFalse(self.vm.is_running())
+        found = 0
+        log = self.vm.get_log()
+        for line in log.split("\n"):
+            if line.startswith("Pattern verification failed"):
+                raise Exception("%s (command #%d)" % (line, found))
+            if re.match("read .*/.* bytes at offset", line):
+                found += 1
+        self.assertEqual(found, self.total_io_cmds,
+                         "Expected output of %d qemu-io commands, found %d" %
+                         (found, self.total_io_cmds))
+
+    # Run x-blockdev-reopen with 'opts' but applying 'newopts'
+    # on top of it. The original 'opts' dict is unmodified
+    def reopen(self, opts, newopts = {}, errmsg = None):
+        opts = copy.deepcopy(opts)
+
+        # Apply the changes from 'newopts' on top of 'opts'
+        for key in newopts:
+            value = newopts[key]
+            # If key has the form "foo.bar" then we need to do
+            # opts["foo"]["bar"] = value, not opts["foo.bar"] = value
+            subdict = opts
+            while key.find('.') != -1:
+                [prefix, key] = key.split('.', 1)
+                subdict = opts[prefix]
+            subdict[key] = value
+
+        result = self.vm.qmp('x-blockdev-reopen', conv_keys = False, **opts)
+        if errmsg:
+            self.assert_qmp(result, 'error/class', 'GenericError')
+            self.assert_qmp(result, 'error/desc', errmsg)
+        else:
+            self.assert_qmp(result, 'return', {})
+
+
+    # Run query-named-block-nodes and return the specified entry
+    def get_node(self, node_name):
+        result = self.vm.qmp('query-named-block-nodes')
+        for node in result['return']:
+            if node['node-name'] == node_name:
+                return node
+        return None
+
+    # Run 'query-named-block-nodes' and compare its output with the
+    # value passed by the user in 'graph'
+    def check_node_graph(self, graph):
+        result = self.vm.qmp('query-named-block-nodes')
+        self.assertEqual(json.dumps(graph,  sort_keys=True),
+                         json.dumps(result, sort_keys=True))
+
+    # This test opens one single disk image (without backing files)
+    # and tries to reopen it with illegal / incorrect parameters.
+    def test_incorrect_parameters_single_file(self):
+        # Open 'hd0' only (no backing files)
+        opts = hd_opts(0)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+        original_graph = self.vm.qmp('query-named-block-nodes')
+
+        # We can reopen the image passing the same options
+        self.reopen(opts)
+
+        # We can also reopen passing a child reference in 'file'
+        self.reopen(opts, {'file': 'hd0-file'})
+
+        # We cannot change any of these
+        self.reopen(opts, {'node-name': 'not-found'}, "Cannot find node named 'not-found'")
+        self.reopen(opts, {'node-name': ''}, "Cannot find node named ''")
+        self.reopen(opts, {'node-name': None}, "Invalid parameter type for 'node-name', expected: string")
+        self.reopen(opts, {'driver': 'raw'}, "Cannot change the option 'driver'")
+        self.reopen(opts, {'driver': ''}, "Invalid parameter ''")
+        self.reopen(opts, {'driver': None}, "Invalid parameter type for 'driver', expected: string")
+        self.reopen(opts, {'file': 'not-found'}, "Cannot change the option 'file'")
+        self.reopen(opts, {'file': ''}, "Cannot change the option 'file'")
+        self.reopen(opts, {'file': None}, "Invalid parameter type for 'file', expected: BlockdevRef")
+        self.reopen(opts, {'file.node-name': 'newname'}, "Cannot change the option 'node-name'")
+        self.reopen(opts, {'file.driver': 'host_device'}, "Cannot change the option 'driver'")
+        self.reopen(opts, {'file.filename': hd_path[1]}, "Cannot change the option 'filename'")
+        self.reopen(opts, {'file.aio': 'native'}, "Cannot change the option 'aio'")
+        self.reopen(opts, {'file.locking': 'off'}, "Cannot change the option 'locking'")
+        self.reopen(opts, {'file.filename': None}, "Invalid parameter type for 'file.filename', expected: string")
+
+        # node-name is optional in BlockdevOptions, but x-blockdev-reopen needs it
+        del opts['node-name']
+        self.reopen(opts, {}, "Node name not specified")
+
+        # Check that nothing has changed
+        self.check_node_graph(original_graph)
+
+        # Remove the node
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+    # This test opens an image with a backing file and tries to reopen
+    # it with illegal / incorrect parameters.
+    def test_incorrect_parameters_backing_file(self):
+        # Open hd1 omitting the backing options (hd0 will be opened
+        # with the default options)
+        opts = hd_opts(1)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+        original_graph = self.vm.qmp('query-named-block-nodes')
+
+        # We can't reopen the image passing the same options, 'backing' is mandatory
+        self.reopen(opts, {}, "backing is missing for 'hd1'")
+
+        # Everything works if we pass 'backing' using the existing node name
+        for node in original_graph['return']:
+            if node['drv'] == iotests.imgfmt and node['file'] == hd_path[0]:
+                backing_node_name = node['node-name']
+        self.reopen(opts, {'backing': backing_node_name})
+
+        # We can't use a non-existing or empty (non-NULL) node as the backing image
+        self.reopen(opts, {'backing': 'not-found'}, "Cannot find device= nor node_name=not-found")
+        self.reopen(opts, {'backing': ''}, "Cannot find device= nor node_name=")
+
+        # We can reopen the image just fine if we specify the backing options
+        opts['backing'] = {'driver': iotests.imgfmt,
+                           'file': {'driver': 'file',
+                                    'filename': hd_path[0]}}
+        self.reopen(opts)
+
+        # We cannot change any of these options
+        self.reopen(opts, {'backing.node-name': 'newname'}, "Cannot change the option 'node-name'")
+        self.reopen(opts, {'backing.driver': 'raw'}, "Cannot change the option 'driver'")
+        self.reopen(opts, {'backing.file.node-name': 'newname'}, "Cannot change the option 'node-name'")
+        self.reopen(opts, {'backing.file.driver': 'host_device'}, "Cannot change the option 'driver'")
+
+        # Check that nothing has changed since the beginning
+        self.check_node_graph(original_graph)
+
+        # Remove the node
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd1')
+        self.assert_qmp(result, 'return', {})
+
+    # Reopen an image several times changing some of its options
+    def test_reopen(self):
+        # Open the hd1 image passing all backing options
+        opts = hd_opts(1)
+        opts['backing'] = hd_opts(0)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+        original_graph = self.vm.qmp('query-named-block-nodes')
+
+        # We can reopen the image passing the same options
+        self.reopen(opts)
+
+        # Reopen in read-only mode
+        self.assert_qmp(self.get_node('hd1'), 'ro', False)
+
+        self.reopen(opts, {'read-only': True})
+        self.assert_qmp(self.get_node('hd1'), 'ro', True)
+        self.reopen(opts)
+        self.assert_qmp(self.get_node('hd1'), 'ro', False)
+
+        # Change the cache options
+        self.assert_qmp(self.get_node('hd1'), 'cache/writeback', True)
+        self.assert_qmp(self.get_node('hd1'), 'cache/direct', False)
+        self.assert_qmp(self.get_node('hd1'), 'cache/no-flush', False)
+        self.reopen(opts, {'cache': { 'direct': True, 'no-flush': True }})
+        self.assert_qmp(self.get_node('hd1'), 'cache/writeback', True)
+        self.assert_qmp(self.get_node('hd1'), 'cache/direct', True)
+        self.assert_qmp(self.get_node('hd1'), 'cache/no-flush', True)
+
+        # Reopen again with the original options
+        self.reopen(opts)
+        self.assert_qmp(self.get_node('hd1'), 'cache/writeback', True)
+        self.assert_qmp(self.get_node('hd1'), 'cache/direct', False)
+        self.assert_qmp(self.get_node('hd1'), 'cache/no-flush', False)
+
+        # Change 'detect-zeroes' and 'discard'
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'off')
+        self.reopen(opts, {'detect-zeroes': 'on'})
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'on')
+        self.reopen(opts, {'detect-zeroes': 'unmap'},
+                    "setting detect-zeroes to unmap is not allowed " +
+                    "without setting discard operation to unmap")
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'on')
+        self.reopen(opts, {'detect-zeroes': 'unmap', 'discard': 'unmap'})
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'unmap')
+        self.reopen(opts)
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'off')
+
+        # Changing 'force-share' is currently not supported
+        self.reopen(opts, {'force-share': True}, "Cannot change the option 'force-share'")
+
+        # Change some qcow2-specific options
+        # No way to test for success other than checking the return message
+        if iotests.imgfmt == 'qcow2':
+            self.reopen(opts, {'l2-cache-entry-size': 128 * 1024},
+                        "L2 cache entry size must be a power of two "+
+                        "between 512 and the cluster size (65536)")
+            self.reopen(opts, {'l2-cache-size': 1024 * 1024,
+                               'cache-size':     512 * 1024},
+                        "l2-cache-size may not exceed cache-size")
+            self.reopen(opts, {'l2-cache-size':        4 * 1024 * 1024,
+                               'refcount-cache-size':  4 * 1024 * 1024,
+                               'l2-cache-entry-size': 32 * 1024})
+            self.reopen(opts, {'pass-discard-request': True})
+
+        # Check that nothing has changed since the beginning
+        # (from the parameters that we can check)
+        self.check_node_graph(original_graph)
+
+        # Check that the node names (other than the top-level one) are optional
+        del opts['file']['node-name']
+        del opts['backing']['node-name']
+        del opts['backing']['file']['node-name']
+        self.reopen(opts)
+        self.check_node_graph(original_graph)
+
+        # Reopen setting backing = null, this removes the backing image from the chain
+        self.reopen(opts, {'backing': None})
+        self.assert_qmp_absent(self.get_node('hd1'), 'image/backing-image')
+
+        # Open the 'hd0' image
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **hd_opts(0))
+        self.assert_qmp(result, 'return', {})
+
+        # Reopen the hd1 image setting 'hd0' as its backing image
+        self.reopen(opts, {'backing': 'hd0'})
+        self.assert_qmp(self.get_node('hd1'), 'image/backing-image/filename', hd_path[0])
+
+        # Check that nothing has changed since the beginning
+        self.reopen(hd_opts(0), {'read-only': True})
+        self.check_node_graph(original_graph)
+
+        # The backing file (hd0) is now a reference, we cannot change backing.* anymore
+        self.reopen(opts, {}, "Cannot change the option 'backing.driver'")
+
+        # We can't remove 'hd0' while it's a backing image of 'hd1'
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+        self.assert_qmp(result, 'error/desc', "Node 'hd0' is busy: node is used as backing hd of 'hd1'")
+
+        # But we can remove both nodes if done in the proper order
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd1')
+        self.assert_qmp(result, 'return', {})
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+    # Reopen a raw image and see the effect of changing the 'offset' option
+    def test_reopen_raw(self):
+        opts = {'driver': 'raw', 'node-name': 'hd0',
+                'file': { 'driver': 'file',
+                          'filename': hd_path[0],
+                          'node-name': 'hd0-file' } }
+
+        # First we create a 2MB raw file, and fill each half with a
+        # different value
+        qemu_img('create', '-f', 'raw', hd_path[0], '2M')
+        qemu_io('-f', 'raw', '-c', 'write -P 0xa0  0 1M', hd_path[0])
+        qemu_io('-f', 'raw', '-c', 'write -P 0xa1 1M 1M', hd_path[0])
+
+        # Open the raw file with QEMU
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Read 1MB from offset 0
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+
+        # Reopen the image with a 1MB offset.
+        # Now the results are different
+        self.reopen(opts, {'offset': 1024*1024})
+        self.run_qemu_io("hd0", "read -P 0xa1  0 1M")
+
+        # Reopen again with the original options.
+        # We get the original results again
+        self.reopen(opts)
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+
+        # Remove the block device
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+    # Omitting an option should reset it to the default value, but if
+    # an option cannot be changed it shouldn't be possible to reset it
+    # to its default value either
+    def test_reset_default_values(self):
+        opts = {'driver': 'qcow2', 'node-name': 'hd0',
+                'file': { 'driver': 'file',
+                          'filename': hd_path[0],
+                          'x-check-cache-dropped': True, # This one can be changed
+                          'locking': 'off',              # This one can NOT be changed
+                          'node-name': 'hd0-file' } }
+
+        # Open the file with QEMU
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # file.x-check-cache-dropped can be changed...
+        self.reopen(opts, { 'file.x-check-cache-dropped': False })
+        # ...and dropped completely (resetting to the default value)
+        del opts['file']['x-check-cache-dropped']
+        self.reopen(opts)
+
+        # file.locking cannot be changed nor reset to the default value
+        self.reopen(opts, { 'file.locking': 'on' }, "Cannot change the option 'locking'")
+        del opts['file']['locking']
+        self.reopen(opts, {}, "Option 'locking' cannot be reset to its default value")
+        # But we can reopen it if we maintain its previous value
+        self.reopen(opts, { 'file.locking': 'off' })
+
+        # Remove the block device
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+    # This test modifies the node graph a few times by changing the
+    # 'backing' option on reopen and verifies that the guest data that
+    # is read afterwards is consistent with the graph changes.
+    def test_io_with_graph_changes(self):
+        opts = []
+
+        # Open hd0, hd1 and hd2 without any backing image
+        for i in range(3):
+            opts.append(hd_opts(i))
+            opts[i]['backing'] = None
+            result = self.vm.qmp('blockdev-add', conv_keys = False, **opts[i])
+            self.assert_qmp(result, 'return', {})
+
+        # hd0
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+        self.run_qemu_io("hd0", "read -P 0    1M 1M")
+        self.run_qemu_io("hd0", "read -P 0    2M 1M")
+
+        # hd1 <- hd0
+        self.reopen(opts[0], {'backing': 'hd1'})
+
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+        self.run_qemu_io("hd0", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd0", "read -P 0    2M 1M")
+
+        # hd1 <- hd0 , hd1 <- hd2
+        self.reopen(opts[2], {'backing': 'hd1'})
+
+        self.run_qemu_io("hd2", "read -P 0     0 1M")
+        self.run_qemu_io("hd2", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd2", "read -P 0xa2 2M 1M")
+
+        # hd1 <- hd2 <- hd0
+        self.reopen(opts[0], {'backing': 'hd2'})
+
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+        self.run_qemu_io("hd0", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd0", "read -P 0xa2 2M 1M")
+
+        # hd2 <- hd0
+        self.reopen(opts[2], {'backing': None})
+
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+        self.run_qemu_io("hd0", "read -P 0    1M 1M")
+        self.run_qemu_io("hd0", "read -P 0xa2 2M 1M")
+
+        # hd2 <- hd1 <- hd0
+        self.reopen(opts[1], {'backing': 'hd2'})
+        self.reopen(opts[0], {'backing': 'hd1'})
+
+        self.run_qemu_io("hd0", "read -P 0xa0  0 1M")
+        self.run_qemu_io("hd0", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd0", "read -P 0xa2 2M 1M")
+
+        # Illegal operation: hd2 is a child of hd1
+        self.reopen(opts[2], {'backing': 'hd1'},
+                    "Making 'hd1' a backing file of 'hd2' would create a cycle")
+
+        # hd2 <- hd0, hd2 <- hd1
+        self.reopen(opts[0], {'backing': 'hd2'})
+
+        self.run_qemu_io("hd1", "read -P 0     0 1M")
+        self.run_qemu_io("hd1", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd1", "read -P 0xa2 2M 1M")
+
+        # More illegal operations
+        self.reopen(opts[2], {'backing': 'hd1'},
+                    "Making 'hd1' a backing file of 'hd2' would create a cycle")
+        self.reopen(opts[2], {'file': 'hd0-file'}, "Cannot change the option 'file'")
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd2')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+        self.assert_qmp(result, 'error/desc', "Node 'hd2' is busy: node is used as backing hd of 'hd0'")
+
+        # hd1 doesn't have a backing file now
+        self.reopen(opts[1], {'backing': None})
+
+        self.run_qemu_io("hd1", "read -P 0     0 1M")
+        self.run_qemu_io("hd1", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd1", "read -P 0    2M 1M")
+
+        # We can't remove the 'backing' option if the image has a
+        # default backing file
+        del opts[1]['backing']
+        self.reopen(opts[1], {}, "backing is missing for 'hd1'")
+
+        self.run_qemu_io("hd1", "read -P 0     0 1M")
+        self.run_qemu_io("hd1", "read -P 0xa1 1M 1M")
+        self.run_qemu_io("hd1", "read -P 0    2M 1M")
+
+    # This test verifies that we can't change the children of a block
+    # device during a reopen operation in a way that would create
+    # cycles in the node graph
+    def test_graph_cycles(self):
+        opts = []
+
+        # Open all three images without backing file
+        for i in range(3):
+            opts.append(hd_opts(i))
+            opts[i]['backing'] = None
+            result = self.vm.qmp('blockdev-add', conv_keys = False, **opts[i])
+            self.assert_qmp(result, 'return', {})
+
+        # hd1 <- hd0, hd1 <- hd2
+        self.reopen(opts[0], {'backing': 'hd1'})
+        self.reopen(opts[2], {'backing': 'hd1'})
+
+        # Illegal: hd2 is backed by hd1
+        self.reopen(opts[1], {'backing': 'hd2'},
+                    "Making 'hd2' a backing file of 'hd1' would create a cycle")
+
+        # hd1 <- hd0 <- hd2
+        self.reopen(opts[2], {'backing': 'hd0'})
+
+        # Illegal: hd2 is backed by hd0, which is backed by hd1
+        self.reopen(opts[1], {'backing': 'hd2'},
+                    "Making 'hd2' a backing file of 'hd1' would create a cycle")
+
+        # Illegal: hd1 cannot point to itself
+        self.reopen(opts[1], {'backing': 'hd1'},
+                    "Making 'hd1' a backing file of 'hd1' would create a cycle")
+
+        # Remove all backing files
+        self.reopen(opts[0])
+        self.reopen(opts[2])
+
+        ##########################################
+        # Add a blkverify node using hd0 and hd1 #
+        ##########################################
+        bvopts = {'driver': 'blkverify',
+                  'node-name': 'bv',
+                  'test': 'hd0',
+                  'raw': 'hd1'}
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **bvopts)
+        self.assert_qmp(result, 'return', {})
+
+        # blkverify doesn't currently allow reopening. TODO: implement this
+        self.reopen(bvopts, {}, "Block format 'blkverify' used by node 'bv'" +
+                    " does not support reopening files")
+
+        # Illegal: hd0 is a child of the blkverify node
+        self.reopen(opts[0], {'backing': 'bv'},
+                    "Making 'bv' a backing file of 'hd0' would create a cycle")
+
+        # Delete the blkverify node
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'bv')
+        self.assert_qmp(result, 'return', {})
+
+    # Misc reopen tests with different block drivers
+    def test_misc_drivers(self):
+        ####################
+        ###### quorum ######
+        ####################
+        for i in range(3):
+            opts = hd_opts(i)
+            # Open all three images without backing file
+            opts['backing'] = None
+            result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+            self.assert_qmp(result, 'return', {})
+
+        opts = {'driver': 'quorum',
+                'node-name': 'quorum0',
+                'children': ['hd0', 'hd1', 'hd2'],
+                'vote-threshold': 2}
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Quorum doesn't currently allow reopening. TODO: implement this
+        self.reopen(opts, {}, "Block format 'quorum' used by node 'quorum0'" +
+                    " does not support reopening files")
+
+        # You can't make quorum0 a backing file of hd0:
+        # hd0 is already a child of quorum0.
+        self.reopen(hd_opts(0), {'backing': 'quorum0'},
+                    "Making 'quorum0' a backing file of 'hd0' would create a cycle")
+
+        # Delete quorum0
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'quorum0')
+        self.assert_qmp(result, 'return', {})
+
+        # Delete hd0, hd1 and hd2
+        for i in range(3):
+            result = self.vm.qmp('blockdev-del', conv_keys = True,
+                                 node_name = 'hd%d' % i)
+            self.assert_qmp(result, 'return', {})
+
+        ######################
+        ###### blkdebug ######
+        ######################
+        opts = {'driver': 'blkdebug',
+                'node-name': 'bd',
+                'config': '/dev/null',
+                'image': hd_opts(0)}
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # blkdebug allows reopening if we keep the same options
+        self.reopen(opts)
+
+        # but it currently does not allow changes
+        self.reopen(opts, {'image': 'hd1'}, "Cannot change the option 'image'")
+        self.reopen(opts, {'align': 33554432}, "Cannot change the option 'align'")
+        self.reopen(opts, {'config': '/non/existent'}, "Cannot change the option 'config'")
+        del opts['config']
+        self.reopen(opts, {}, "Option 'config' cannot be reset to its default value")
+
+        # Delete the blkdebug node
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'bd')
+        self.assert_qmp(result, 'return', {})
+
+        ##################
+        ###### null ######
+        ##################
+        opts = {'driver': 'null-aio', 'node-name': 'root', 'size': 1024}
+
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # 1 << 30 is the default value, but we cannot change it explicitly
+        self.reopen(opts, {'size': (1 << 30)}, "Cannot change the option 'size'")
+
+        # We cannot change 'size' back to its default value either
+        del opts['size']
+        self.reopen(opts, {}, "Option 'size' cannot be reset to its default value")
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'root')
+        self.assert_qmp(result, 'return', {})
+
+        ##################
+        ###### file ######
+        ##################
+        opts = hd_opts(0)
+        opts['file']['locking'] = 'on'
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # 'locking' cannot be changed
+        del opts['file']['locking']
+        self.reopen(opts, {'file.locking': 'on'})
+        self.reopen(opts, {'file.locking': 'off'}, "Cannot change the option 'locking'")
+        self.reopen(opts, {}, "Option 'locking' cannot be reset to its default value")
+
+        # Trying to reopen the 'file' node directly does not make a difference
+        opts = opts['file']
+        self.reopen(opts, {'locking': 'on'})
+        self.reopen(opts, {'locking': 'off'}, "Cannot change the option 'locking'")
+        self.reopen(opts, {}, "Option 'locking' cannot be reset to its default value")
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+        ######################
+        ###### throttle ######
+        ######################
+        opts = { 'qom-type': 'throttle-group', 'id': 'group0',
+                 'props': { 'limits': { 'iops-total': 1000 } } }
+        result = self.vm.qmp('object-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        opts = { 'qom-type': 'throttle-group', 'id': 'group1',
+                 'props': { 'limits': { 'iops-total': 2000 } } }
+        result = self.vm.qmp('object-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Add a throttle filter with group = group0
+        opts = { 'driver': 'throttle', 'node-name': 'throttle0',
+                 'throttle-group': 'group0', 'file': hd_opts(0) }
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # We can reopen it if we keep the same options
+        self.reopen(opts)
+
+        # We can also reopen if 'file' is a reference to the child
+        self.reopen(opts, {'file': 'hd0'})
+
+        # This is illegal
+        self.reopen(opts, {'throttle-group': 'notfound'}, "Throttle group 'notfound' does not exist")
+
+        # But it's possible to change the group to group1
+        self.reopen(opts, {'throttle-group': 'group1'})
+
+        # Now group1 is in use, it cannot be deleted
+        result = self.vm.qmp('object-del', id = 'group1')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+        self.assert_qmp(result, 'error/desc', "object 'group1' is in use, can not be deleted")
+
+        # Default options, this switches the group back to group0
+        self.reopen(opts)
+
+        # So now we cannot delete group0
+        result = self.vm.qmp('object-del', id = 'group0')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+        self.assert_qmp(result, 'error/desc', "object 'group0' is in use, can not be deleted")
+
+        # But group1 is free this time, and it can be deleted
+        result = self.vm.qmp('object-del', id = 'group1')
+        self.assert_qmp(result, 'return', {})
+
+        # Let's delete the filter node
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'throttle0')
+        self.assert_qmp(result, 'return', {})
+
+        # And we can finally get rid of group0
+        result = self.vm.qmp('object-del', id = 'group0')
+        self.assert_qmp(result, 'return', {})
+
+    # If an image has a backing file then the 'backing' option must be
+    # passed on reopen. We don't allow leaving the option out in this
+    # case because it's unclear what the correct semantics would be.
+    def test_missing_backing_options_1(self):
+        # hd2
+        opts = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # hd0
+        opts = hd_opts(0)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # hd0 has no backing file: we can omit the 'backing' option
+        self.reopen(opts)
+
+        # hd2 <- hd0
+        self.reopen(opts, {'backing': 'hd2'})
+
+        # hd0 has a backing file: we must set the 'backing' option
+        self.reopen(opts, {}, "backing is missing for 'hd0'")
+
+        # hd2 can't be removed because it's the backing file of hd0
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd2')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+        self.assert_qmp(result, 'error/desc', "Node 'hd2' is busy: node is used as backing hd of 'hd0'")
+
+        # Detach hd2 from hd0.
+        self.reopen(opts, {'backing': None})
+        self.reopen(opts, {}, "backing is missing for 'hd0'")
+
+        # Remove both hd0 and hd2
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd2')
+        self.assert_qmp(result, 'return', {})
+
+    # If an image has default backing file (as part of its metadata)
+    # then the 'backing' option must be passed on reopen. We don't
+    # allow leaving the option out in this case because it's unclear
+    # what the correct semantics would be.
+    def test_missing_backing_options_2(self):
+        # hd0 <- hd1
+        # (hd0 is hd1's default backing file)
+        opts = hd_opts(1)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # hd1 has a backing file: we can't omit the 'backing' option
+        self.reopen(opts, {}, "backing is missing for 'hd1'")
+
+        # Let's detach the backing file
+        self.reopen(opts, {'backing': None})
+
+        # No backing file attached to hd1 now, but we still can't omit the 'backing' option
+        self.reopen(opts, {}, "backing is missing for 'hd1'")
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd1')
+        self.assert_qmp(result, 'return', {})
+
+    # Test that making 'backing' a reference to an existing child
+    # keeps its current options
+    def test_backing_reference(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        # Enable 'detect-zeroes' on all three nodes
+        opts['detect-zeroes'] = 'on'
+        opts['backing']['detect-zeroes'] = 'on'
+        opts['backing']['backing']['detect-zeroes'] = 'on'
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Reopen the chain passing the minimum amount of required options.
+        # By making 'backing' a reference to hd1 (instead of a sub-dict)
+        # we tell QEMU to keep its current set of options.
+        opts = {'driver': iotests.imgfmt,
+                'node-name': 'hd0',
+                'file': 'hd0-file',
+                'backing': 'hd1' }
+        self.reopen(opts)
+
+        # This has reset 'detect-zeroes' on hd0, but not on hd1 and hd2.
+        self.assert_qmp(self.get_node('hd0'), 'detect_zeroes', 'off')
+        self.assert_qmp(self.get_node('hd1'), 'detect_zeroes', 'on')
+        self.assert_qmp(self.get_node('hd2'), 'detect_zeroes', 'on')
+
+    # Test what happens if the graph changes due to other operations
+    # such as block-stream
+    def test_block_stream_1(self):
+        # hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = None
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Stream hd1 into hd0 and wait until it's done
+        result = self.vm.qmp('block-stream', conv_keys = True, job_id = 'stream0', device = 'hd0')
+        self.assert_qmp(result, 'return', {})
+        self.wait_until_completed(drive = 'stream0')
+
+        # Now we have only hd0
+        self.assertEqual(self.get_node('hd1'), None)
+
+        # We have backing.* options but there's no backing file anymore
+        self.reopen(opts, {}, "Cannot change the option 'backing.driver'")
+
+        # If we remove the 'backing' option then we can reopen hd0 just fine
+        del opts['backing']
+        self.reopen(opts)
+
+        # We can also reopen hd0 if we set 'backing' to null
+        self.reopen(opts, {'backing': None})
+
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+
+    # Another block_stream test
+    def test_block_stream_2(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Stream hd1 into hd0 and wait until it's done
+        result = self.vm.qmp('block-stream', conv_keys = True, job_id = 'stream0',
+                             device = 'hd0', base_node = 'hd2')
+        self.assert_qmp(result, 'return', {})
+        self.wait_until_completed(drive = 'stream0')
+
+        # The chain is hd2 <- hd0 now. hd1 is missing
+        self.assertEqual(self.get_node('hd1'), None)
+
+        # The backing options in the dict were meant for hd1, but we cannot
+        # use them with hd2 because hd1 had a backing file while hd2 does not.
+        self.reopen(opts, {}, "Cannot change the option 'backing.driver'")
+
+        # If we remove hd1's options from the dict then things work fine
+        opts['backing'] = opts['backing']['backing']
+        self.reopen(opts)
+
+        # We can also reopen hd0 if we use a reference to the backing file
+        self.reopen(opts, {'backing': 'hd2'})
+
+        # But we cannot leave the option out
+        del opts['backing']
+        self.reopen(opts, {}, "backing is missing for 'hd0'")
+
+        # Now we can delete hd0 (and hd2)
+        result = self.vm.qmp('blockdev-del', conv_keys = True, node_name = 'hd0')
+        self.assert_qmp(result, 'return', {})
+        self.assertEqual(self.get_node('hd2'), None)
+
+    # Reopen the chain during a block-stream job (from hd1 to hd0)
+    def test_block_stream_3(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # hd2 <- hd0
+        result = self.vm.qmp('block-stream', conv_keys = True, job_id = 'stream0',
+                             device = 'hd0', base_node = 'hd2', speed = 512 * 1024)
+        self.assert_qmp(result, 'return', {})
+
+        # We can't remove hd2 while the stream job is ongoing
+        opts['backing']['backing'] = None
+        self.reopen(opts, {}, "Cannot change 'backing' link from 'hd1' to 'hd2'")
+
+        # We can't remove hd1 while the stream job is ongoing
+        opts['backing'] = None
+        self.reopen(opts, {}, "Cannot change 'backing' link from 'hd0' to 'hd1'")
+
+        self.wait_until_completed(drive = 'stream0')
+
+    # Reopen the chain during a block-stream job (from hd2 to hd1)
+    def test_block_stream_4(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # hd1 <- hd0
+        result = self.vm.qmp('block-stream', conv_keys = True, job_id = 'stream0',
+                             device = 'hd1', speed = 512 * 1024)
+        self.assert_qmp(result, 'return', {})
+
+        # We can't reopen with the original options because that would
+        # make hd1 read-only and block-stream requires it to be read-write
+        self.reopen(opts, {}, "Can't set node 'hd1' to r/o with copy-on-read enabled")
+
+        # We can't remove hd2 while the stream job is ongoing
+        opts['backing']['backing'] = None
+        self.reopen(opts, {'backing.read-only': False}, "Cannot change 'backing' link from 'hd1' to 'hd2'")
+
+        # We can detach hd1 from hd0 because it doesn't affect the stream job
+        opts['backing'] = None
+        self.reopen(opts)
+
+        self.wait_until_completed(drive = 'stream0')
+
+    # Reopen the chain during a block-commit job (from hd0 to hd2)
+    def test_block_commit_1(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('block-commit', conv_keys = True, job_id = 'commit0',
+                             device = 'hd0', speed = 1024 * 1024)
+        self.assert_qmp(result, 'return', {})
+
+        # We can't remove hd2 while the commit job is ongoing
+        opts['backing']['backing'] = None
+        self.reopen(opts, {}, "Cannot change 'backing' link from 'hd1' to 'hd2'")
+
+        # We can't remove hd1 while the commit job is ongoing
+        opts['backing'] = None
+        self.reopen(opts, {}, "Cannot change 'backing' link from 'hd0' to 'hd1'")
+
+        event = self.vm.event_wait(name='BLOCK_JOB_READY')
+        self.assert_qmp(event, 'data/device', 'commit0')
+        self.assert_qmp(event, 'data/type', 'commit')
+        self.assert_qmp_absent(event, 'data/error')
+
+        result = self.vm.qmp('block-job-complete', device='commit0')
+        self.assert_qmp(result, 'return', {})
+
+        self.wait_until_completed(drive = 'commit0')
+
+    # Reopen the chain during a block-commit job (from hd1 to hd2)
+    def test_block_commit_2(self):
+        # hd2 <- hd1 <- hd0
+        opts = hd_opts(0)
+        opts['backing'] = hd_opts(1)
+        opts['backing']['backing'] = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('block-commit', conv_keys = True, job_id = 'commit0',
+                             device = 'hd0', top_node = 'hd1', speed = 1024 * 1024)
+        self.assert_qmp(result, 'return', {})
+
+        # We can't remove hd2 while the commit job is ongoing
+        opts['backing']['backing'] = None
+        self.reopen(opts, {}, "Cannot change the option 'backing.driver'")
+
+        # We can't remove hd1 while the commit job is ongoing
+        opts['backing'] = None
+        self.reopen(opts, {}, "Cannot change backing link if 'hd0' has an implicit backing file")
+
+        # hd2 <- hd0
+        self.wait_until_completed(drive = 'commit0')
+
+        self.assert_qmp(self.get_node('hd0'), 'ro', False)
+        self.assertEqual(self.get_node('hd1'), None)
+        self.assert_qmp(self.get_node('hd2'), 'ro', True)
+
+    # We don't allow setting a backing file that uses a different AioContext
+    def test_iothreads(self):
+        opts = hd_opts(0)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        opts2 = hd_opts(2)
+        result = self.vm.qmp('blockdev-add', conv_keys = False, **opts2)
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('object-add', qom_type='iothread', id='iothread0')
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('object-add', qom_type='iothread', id='iothread1')
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd0', iothread='iothread0')
+        self.assert_qmp(result, 'return', {})
+
+        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
+
+        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread1')
+        self.assert_qmp(result, 'return', {})
+
+        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
+
+        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread0')
+        self.assert_qmp(result, 'return', {})
+
+        self.reopen(opts, {'backing': 'hd2'})
+
+if __name__ == '__main__':
+    iotests.main(supported_fmts=["qcow2"])
diff --git a/tests/qemu-iotests/245.out b/tests/qemu-iotests/245.out
new file mode 100644
index 0000000000..71009c239f
--- /dev/null
+++ b/tests/qemu-iotests/245.out
@@ -0,0 +1,5 @@
+..................
+----------------------------------------------------------------------
+Ran 18 tests
+
+OK
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 36100b803c..66ab708d4a 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -243,3 +243,4 @@
 242 rw auto quick
 243 rw auto quick
 244 rw auto quick
+245 rw auto
diff --git a/tests/virtio-blk-test.c b/tests/virtio-blk-test.c
index b02be0274e..b65365934b 100644
--- a/tests/virtio-blk-test.c
+++ b/tests/virtio-blk-test.c
@@ -751,7 +751,7 @@ static void *virtio_blk_test_setup(GString *cmd_line, void *arg)
     char *tmp_path = drive_create();
 
     g_string_append_printf(cmd_line,
-                           " -drive if=none,id=drive0,file=%s,format=raw "
+                           " -drive if=none,id=drive0,file=%s,format=raw,auto-read-only=off "
                            "-drive if=none,id=drive1,file=null-co://,format=raw ",
                            tmp_path);