qcow2: Write feature table only for v3 images

Version 2 images don't have feature bits, so writing a feature table to
those images is kind of pointless.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

block/qcow2.c

@@ -1895,31 +1895,33 @@ int qcow2_update_header(BlockDriverState *bs)
     }
 
     /* Feature table */
-    Qcow2Feature features[] = {
-        {
-            .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
-            .bit  = QCOW2_INCOMPAT_DIRTY_BITNR,
-            .name = "dirty bit",
-        },
-        {
-            .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
-            .bit  = QCOW2_INCOMPAT_CORRUPT_BITNR,
-            .name = "corrupt bit",
-        },
-        {
-            .type = QCOW2_FEAT_TYPE_COMPATIBLE,
-            .bit  = QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
-            .name = "lazy refcounts",
-        },
-    };
+    if (s->qcow_version >= 3) {
+        Qcow2Feature features[] = {
+            {
+                .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
+                .bit  = QCOW2_INCOMPAT_DIRTY_BITNR,
+                .name = "dirty bit",
+            },
+            {
+                .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
+                .bit  = QCOW2_INCOMPAT_CORRUPT_BITNR,
+                .name = "corrupt bit",
+            },
+            {
+                .type = QCOW2_FEAT_TYPE_COMPATIBLE,
+                .bit  = QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
+                .name = "lazy refcounts",
+            },
+        };
 
-    ret = header_ext_add(buf, QCOW2_EXT_MAGIC_FEATURE_TABLE,
-                         features, sizeof(features), buflen);
-    if (ret < 0) {
-        goto fail;
+        ret = header_ext_add(buf, QCOW2_EXT_MAGIC_FEATURE_TABLE,
+                             features, sizeof(features), buflen);
+        if (ret < 0) {
+            goto fail;
+        }
+        buf += ret;
+        buflen -= ret;
     }
-    buf += ret;
-    buflen -= ret;
 
     /* Keep unknown header extensions */
     QLIST_FOREACH(uext, &s->unknown_header_ext, next) {

tests/qemu-iotests/031.out

@@ -52,11 +52,6 @@ autoclear_features        0x0
 refcount_order            4
 header_length             72
 
-Header extension:
-magic                     0x6803f857
-length                    144
-data                      <binary>
-
 Header extension:
 magic                     0x12345678
 length                    31
@@ -68,7 +63,7 @@ No errors were found on the image.
 
 magic                     0x514649fb
 version                   2
-backing_file_offset       0x128
+backing_file_offset       0x90
 backing_file_size         0x17
 cluster_bits              16
 size                      67108864
@@ -90,11 +85,6 @@ magic                     0xe2792aca
 length                    11
 data                      'host_device'
 
-Header extension:
-magic                     0x6803f857
-length                    144
-data                      <binary>
-
 Header extension:
 magic                     0x12345678
 length                    31

tests/qemu-iotests/061.out

@@ -43,11 +43,6 @@ autoclear_features        0x0
 refcount_order            4
 header_length             72
 
-Header extension:
-magic                     0x6803f857
-length                    144
-data                      <binary>
-
 read 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 No errors were found on the image.
@@ -105,11 +100,6 @@ autoclear_features        0x0
 refcount_order            4
 header_length             72
 
-Header extension:
-magic                     0x6803f857
-length                    144
-data                      <binary>
-
 read 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 No errors were found on the image.
@@ -155,11 +145,6 @@ autoclear_features        0x0
 refcount_order            4
 header_length             72
 
-Header extension:
-magic                     0x6803f857
-length                    144
-data                      <binary>
-
 No errors were found on the image.
 
 === Testing version upgrade and resize ===