block: Add BlockDriver.bdrv_gather_child_options

Some follow-up patches will rework the way bs->full_open_options is
refreshed in bdrv_refresh_filename(). The new implementation will remove
the need for the block drivers' bdrv_refresh_filename() implementations
to set bs->full_open_options; instead, it will be generic and use static
information from each block driver.

However, by implementing bdrv_gather_child_options(), block drivers will
still be able to override the way the full_open_options of their
children are incorporated into their own.

We need to implement this function for VMDK because we have to prevent
the generic implementation from gathering the options of all children:
It is not possible to specify options for the extents through the
runtime options.

For quorum, the child names that would be used by the generic
implementation and the ones that we actually (currently) want to use
differ. See quorum_gather_child_options() for more information.

Note that both of these are cases which are not ideal: In case of VMDK
it would probably be nice to be able to specify options for all extents.
In case of quorum, the current runtime option structure is simply broken
and needs to be fixed (but that is left for another patch).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190201192935.18394-23-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/block/quorum.c b/block/quorum.c
index 1af6458..3984f0a 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1094,6 +1094,45 @@ static void quorum_refresh_filename(BlockDriverState *bs, QDict *options)
     bs->full_open_options = opts;
 }
 
+static void quorum_gather_child_options(BlockDriverState *bs, QDict *target,
+                                        bool backing_overridden)
+{
+    BDRVQuorumState *s = bs->opaque;
+    QList *children_list;
+    int i;
+
+    /*
+     * The generic implementation for gathering child options in
+     * bdrv_refresh_filename() would use the names of the children
+     * as specified for bdrv_open_child() or bdrv_attach_child(),
+     * which is "children.%u" with %u being a value
+     * (s->next_child_index) that is incremented each time a new child
+     * is added (and never decremented).  Since children can be
+     * deleted at runtime, there may be gaps in that enumeration.
+     * When creating a new quorum BDS and specifying the children for
+     * it through runtime options, the enumeration used there may not
+     * have any gaps, though.
+     *
+     * Therefore, we have to create a new gap-less enumeration here
+     * (which we can achieve by simply putting all of the children's
+     * full_open_options into a QList).
+     *
+     * XXX: Note that there are issues with the current child option
+     *      structure quorum uses (such as the fact that children do
+     *      not really have unique permanent names).  Therefore, this
+     *      is going to have to change in the future and ideally we
+     *      want quorum to be covered by the generic implementation.
+     */
+
+    children_list = qlist_new();
+    qdict_put(target, "children", children_list);
+
+    for (i = 0; i < s->num_children; i++) {
+        qlist_append(children_list,
+                     qobject_ref(s->children[i]->bs->full_open_options));
+    }
+}
+
 static char *quorum_dirname(BlockDriverState *bs, Error **errp)
 {
     /* In general, there are multiple BDSs with different dirnames below this
@@ -1121,6 +1160,7 @@ static BlockDriver bdrv_quorum = {
     .bdrv_open                          = quorum_open,
     .bdrv_close                         = quorum_close,
     .bdrv_refresh_filename              = quorum_refresh_filename,
+    .bdrv_gather_child_options          = quorum_gather_child_options,
     .bdrv_dirname                       = quorum_dirname,
 
     .bdrv_co_flush_to_disk              = quorum_co_flush,