@@ -2823,8 +2823,15 @@ int qcow2_update_header(BlockDriverState *bs)
buflen -= ret;
}
- /* Feature table */
- if (s->qcow_version >= 3) {
+ /*
+ * Feature table. A mere 8 feature names occupies 392 bytes, and
+ * when coupled with the v3 minimum header of 104 bytes plus the
+ * 8-byte end-of-extension marker, that would leave only 8 bytes
+ * for a backing file name in an image with 512-byte clusters.
+ * Thus, we choose to omit this header for cluster sizes 4k and
+ * smaller.
+ */
+ if (s->qcow_version >= 3 && s->cluster_size > 4096) {
static const Qcow2Feature features[] = {
{
.type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
@@ -44,8 +44,10 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
_supported_fmt qcow2
_supported_proto file
# Only qcow2v3 and later supports feature bits;
-# qcow2.py does not support external data files
-_unsupported_imgopts 'compat=0.10' data_file
+# qcow2.py does not support external data files;
+# this test requires a cluster size large enough for the feature table
+_unsupported_imgopts 'compat=0.10' data_file \
+ 'cluster_size=\(512\|1024\|2048\|4096\)'
echo
echo === Image with unknown incompatible feature bit ===
@@ -44,8 +44,10 @@ _supported_os Linux
# Conversion between different compat versions can only really work
# with refcount_bits=16;
# we have explicit tests for data_file here, but the whole test does
-# not work with it
-_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file
+# not work with it;
+# we have explicit tests for various cluster sizes, the remaining tests
+# require the default 64k cluster
+_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file cluster_size
echo
echo "=== Testing version downgrade with zero expansion ==="