This field should be used by block drivers acting as filters which have
only a single child BDS which is referenced through the "file" field of
the BDS.
Setting this field allows other block functions to "access" the child
BDS, for instance in bdrv_recurse_is_first_non_filter(). Therefore, it
should not be set if the block layer should not have access to the child
through the filter.
Signed-off-by: Max Reitz <mre...@redhat.com>
---
block.c | 4 ++++
include/block/block_int.h | 7 +++++++
2 files changed, 11 insertions(+)
diff --git a/block.c b/block.c
index 06fbc0a..aec325f 100644
--- a/block.c
+++ b/block.c
@@ -5418,6 +5418,10 @@ bool bdrv_recurse_is_first_non_filter(BlockDriverState
*bs,
return bs->drv->bdrv_recurse_is_first_non_filter(bs, candidate);
}
+ if (bs->drv->has_single_child) {
+ return bdrv_recurse_is_first_non_filter(bs->file, candidate);
+ }
+
/* the driver is a block filter but don't allow to recurse -> return false
*/
return false;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 4fc5ea8..7815587 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -78,6 +78,13 @@ struct BlockDriver {
/* set to true if the BlockDriver is a block filter */
bool is_filter;
+ /* Set to true if the BlockDriver is a filter with a single child
referenced
+ * through the "file" field in the BDS. This allows the block layer to
+ * access that child through the filter (e.g., for
+ * bdrv_recurse_is_first_non_filter()); if this is not desired, set it to
+ * false (the "file" field should not have been used in this case anyway,
+ * though). */
+ bool has_single_child;
/* for snapshots block filter like Quorum can implement the
* following recursive callback.
* It's purpose is to recurse on the filter children while calling
--
1.9.0
