vmdk: fix metadata write regression

Commit "cdeaf1f vmdk: add bdrv_co_write_zeroes" causes a regression on
writes. It writes metadata after every write instead of doing it only once
for each cluster.

vmdk_pwritev() writes metadata whenever m_data is set as valid so this patch
sets m_data as valid only when we have a new cluster which hasn't been
allocated before or a zero grain.

Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
Message-id: 20160707084249.29084-1-fullmanet@gmail.com
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/vmdk.c

@@ -1202,13 +1202,6 @@ static int get_cluster_offset(BlockDriverState *bs,
     l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;
     cluster_sector = le32_to_cpu(l2_table[l2_index]);
 
-    if (m_data) {
-        m_data->valid = 1;
-        m_data->l1_index = l1_index;
-        m_data->l2_index = l2_index;
-        m_data->l2_offset = l2_offset;
-        m_data->l2_cache_entry = &l2_table[l2_index];
-    }
     if (extent->has_zero_grain && cluster_sector == VMDK_GTE_ZEROED) {
         zeroed = true;
     }
@@ -1231,6 +1224,13 @@ static int get_cluster_offset(BlockDriverState *bs,
         if (ret) {
             return ret;
         }
+        if (m_data) {
+            m_data->valid = 1;
+            m_data->l1_index = l1_index;
+            m_data->l2_index = l2_index;
+            m_data->l2_offset = l2_offset;
+            m_data->l2_cache_entry = &l2_table[l2_index];
+        }
     }
     *cluster_offset = cluster_sector << BDRV_SECTOR_BITS;
     return VMDK_OK;