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 <mre...@redhat.com>
---
include/block/block.h | 1 +
block.c | 23 +++++++++++++++++++++++
2 files changed, 24 insertions(+)
diff --git a/include/block/block.h b/include/block/block.h
index 0080fe1311..a905a5ec05 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -538,6 +538,7 @@ BlockDriverState *bdrv_next(BdrvNextIterator *it);
void bdrv_next_cleanup(BdrvNextIterator *it);
BlockDriverState *bdrv_next_monitor_owned(BlockDriverState *bs);
+bool bdrv_supports_compressed_writes(BlockDriverState *bs);
void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
void *opaque, bool read_only);
const char *bdrv_get_node_name(const BlockDriverState *bs);
diff --git a/block.c b/block.c
index 76277ea4e0..6449f3a11d 100644
--- a/block.c
+++ b/block.c
@@ -5044,6 +5044,29 @@ bool bdrv_is_sg(BlockDriverState *bs)
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;
--
2.26.2
