block: Add bdrv_supports_compressed_writes()
Filters cannot compress data themselves but they have to implement
.bdrv_co_pwritev_compressed() still (or they cannot forward compressed
writes). Therefore, checking whether
bs->drv->bdrv_co_pwritev_compressed is non-NULL is not sufficient to
know whether the node can actually handle compressed writes. This
function looks down the filter chain to see whether there is a
non-filter that can actually convert the compressed writes into
compressed data (and thus normal writes).
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index f5eabaa..c09a766 100644
--- a/block.c
+++ b/block.c
@@ -5065,6 +5065,29 @@
return bs->sg;
}
+/**
+ * Return whether the given node supports compressed writes.
+ */
+bool bdrv_supports_compressed_writes(BlockDriverState *bs)
+{
+ BlockDriverState *filtered;
+
+ if (!bs->drv || !block_driver_can_compress(bs->drv)) {
+ return false;
+ }
+
+ filtered = bdrv_filter_bs(bs);
+ if (filtered) {
+ /*
+ * Filters can only forward compressed writes, so we have to
+ * check the child.
+ */
+ return bdrv_supports_compressed_writes(filtered);
+ }
+
+ return true;
+}
+
const char *bdrv_get_format_name(BlockDriverState *bs)
{
return bs->drv ? bs->drv->format_name : NULL;
