1 files changed, 26 insertions, 7 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index d1da3d91db..2bb536b014 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -177,7 +177,7 @@ static ssize_t qcow2_crypto_hdr_write_func(QCryptoBlock *block, size_t offset,
 }
 
 
-/* 
+/*
  * read qcow2 extension and fill bs
  * start reading from start_offset
  * finish reading upon magic of value 0 or when end_offset reached
@@ -2823,9 +2823,16 @@ int qcow2_update_header(BlockDriverState *bs)
         buflen -= ret;
     }
 
-    /* Feature table */
-    if (s->qcow_version >= 3) {
-        Qcow2Feature features[] = {
+    /*
+     * 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,
                 .bit  = QCOW2_INCOMPAT_DIRTY_BITNR,
@@ -2846,6 +2853,16 @@ int qcow2_update_header(BlockDriverState *bs)
                 .bit  = QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
                 .name = "lazy refcounts",
             },
+            {
+                .type = QCOW2_FEAT_TYPE_AUTOCLEAR,
+                .bit  = QCOW2_AUTOCLEAR_BITMAPS_BITNR,
+                .name = "bitmaps",
+            },
+            {
+                .type = QCOW2_FEAT_TYPE_AUTOCLEAR,
+                .bit  = QCOW2_AUTOCLEAR_DATA_FILE_RAW_BITNR,
+                .name = "raw external data",
+            },
         };
 
         ret = header_ext_add(buf, QCOW2_EXT_MAGIC_FEATURE_TABLE,
@@ -3255,7 +3272,7 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
      * inconsistency later.
      *
      * We do need a refcount table because growing the refcount table means
-     * allocating two new refcount blocks - the seconds of which would be at
+     * allocating two new refcount blocks - the second of which would be at
      * 2 GB for 64k clusters, and we don't want to have a 2 GB initial file
      * size for any qcow2 image.
      */
@@ -3500,7 +3517,7 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
         goto out;
     }
 
-    /* Want a backing file? There you go.*/
+    /* Want a backing file? There you go. */
     if (qcow2_opts->has_backing_file) {
         const char *backing_format = NULL;
 
@@ -3558,7 +3575,9 @@ out:
     return ret;
 }
 
-static int coroutine_fn qcow2_co_create_opts(const char *filename, QemuOpts *opts,
+static int coroutine_fn qcow2_co_create_opts(BlockDriver *drv,
+                                             const char *filename,
+                                             QemuOpts *opts,
                                              Error **errp)
 {
     BlockdevCreateOptions *create_options = NULL;