diff --git a/block/vmdk.c b/block/vmdk.c
index 8dc58a8..f637d98 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -665,26 +665,31 @@ static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data)
     return 0;
 }
 
-static uint64_t get_cluster_offset(BlockDriverState *bs,
+static int get_cluster_offset(BlockDriverState *bs,
                                     VmdkExtent *extent,
                                     VmdkMetaData *m_data,
-                                    uint64_t offset, int allocate)
+                                    uint64_t offset,
+                                    int allocate,
+                                    uint64_t *cluster_offset)
 {
     unsigned int l1_index, l2_offset, l2_index;
     int min_index, i, j;
     uint32_t min_count, *l2_table, tmp = 0;
-    uint64_t cluster_offset;
 
     if (m_data)
         m_data->valid = 0;
+    if (extent->flat) {
+        *cluster_offset = 0;
+        return 0;
+    }
 
     l1_index = (offset >> 9) / extent->l1_entry_sectors;
     if (l1_index >= extent->l1_size) {
-        return 0;
+        return -1;
     }
     l2_offset = extent->l1_table[l1_index];
     if (!l2_offset) {
-        return 0;
+        return -1;
     }
     for (i = 0; i < L2_CACHE_SIZE; i++) {
         if (l2_offset == extent->l2_cache_offsets[i]) {
@@ -714,28 +719,29 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
                 l2_table,
                 extent->l2_size * sizeof(uint32_t)
             ) != extent->l2_size * sizeof(uint32_t)) {
-        return 0;
+        return -1;
     }
 
     extent->l2_cache_offsets[min_index] = l2_offset;
     extent->l2_cache_counts[min_index] = 1;
  found:
     l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;
-    cluster_offset = le32_to_cpu(l2_table[l2_index]);
+    *cluster_offset = le32_to_cpu(l2_table[l2_index]);
 
-    if (!cluster_offset) {
-        if (!allocate)
-            return 0;
+    if (!*cluster_offset) {
+        if (!allocate) {
+            return -1;
+        }
 
         // Avoid the L2 tables update for the images that have snapshots.
-        cluster_offset = bdrv_getlength(extent->file);
+        *cluster_offset = bdrv_getlength(extent->file);
         bdrv_truncate(
             extent->file,
-            cluster_offset + (extent->cluster_sectors << 9)
+            *cluster_offset + (extent->cluster_sectors << 9)
         );
 
-        cluster_offset >>= 9;
-        tmp = cpu_to_le32(cluster_offset);
+        *cluster_offset >>= 9;
+        tmp = cpu_to_le32(*cluster_offset);
         l2_table[l2_index] = tmp;
 
         /* First of all we write grain itself, to avoid race condition
@@ -744,8 +750,8 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
          * or inappropriate VM shutdown.
          */
         if (get_whole_cluster(
-                bs, extent, cluster_offset, offset, allocate) == -1)
-            return 0;
+                bs, extent, *cluster_offset, offset, allocate) == -1)
+            return -1;
 
         if (m_data) {
             m_data->offset = tmp;
@@ -755,8 +761,8 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
             m_data->valid = 1;
         }
     }
-    cluster_offset <<= 9;
-    return cluster_offset;
+    *cluster_offset <<= 9;
+    return 0;
 }
 
 static VmdkExtent *find_extent(BDRVVmdkState *s,
@@ -780,7 +786,6 @@ static int vmdk_is_allocated(BlockDriverState *bs, int64_t sector_num,
                              int nb_sectors, int *pnum)
 {
     BDRVVmdkState *s = bs->opaque;
-
     int64_t index_in_cluster, n, ret;
     uint64_t offset;
     VmdkExtent *extent;
@@ -789,15 +794,13 @@ static int vmdk_is_allocated(BlockDriverState *bs, int64_t sector_num,
     if (!extent) {
         return 0;
     }
-    if (extent->flat) {
-        n = extent->end_sector - sector_num;
-        ret = 1;
-    } else {
-        offset = get_cluster_offset(bs, extent, NULL, sector_num * 512, 0);
-        index_in_cluster = sector_num % extent->cluster_sectors;
-        n = extent->cluster_sectors - index_in_cluster;
-        ret = offset ? 1 : 0;
-    }
+    ret = get_cluster_offset(bs, extent, NULL,
+                            sector_num * 512, 0, &offset);
+    /* get_cluster_offset returning 0 means success */
+    ret = !ret;
+
+    index_in_cluster = sector_num % extent->cluster_sectors;
+    n = extent->cluster_sectors - index_in_cluster;
     if (n > nb_sectors)
         n = nb_sectors;
     *pnum = n;
@@ -818,14 +821,15 @@ static int vmdk_read(BlockDriverState *bs, int64_t sector_num,
         if (!extent) {
             return -EIO;
         }
-        cluster_offset = get_cluster_offset(
-                            bs, extent, NULL, sector_num << 9, 0);
+        ret = get_cluster_offset(
+                            bs, extent, NULL,
+                            sector_num << 9, 0, &cluster_offset);
         index_in_cluster = sector_num % extent->cluster_sectors;
         n = extent->cluster_sectors - index_in_cluster;
         if (n > nb_sectors)
             n = nb_sectors;
-        if (!cluster_offset) {
-            // try to read from parent image, if exist
+        if (ret) {
+            /* if not allocated, try to read from parent image, if exist */
             if (bs->backing_hd) {
                 if (!vmdk_is_cid_valid(bs))
                     return -1;
@@ -851,7 +855,7 @@ static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
 {
     BDRVVmdkState *s = bs->opaque;
     VmdkExtent *extent = NULL;
-    int n;
+    int n, ret;
     int64_t index_in_cluster;
     uint64_t cluster_offset;
     VmdkMetaData m_data;
@@ -869,13 +873,14 @@ static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
         if (!extent) {
             return -EIO;
         }
-        cluster_offset = get_cluster_offset(
+        ret = get_cluster_offset(
                                 bs,
                                 extent,
                                 &m_data,
-                                sector_num << 9, 1);
-        if (!cluster_offset) {
-            return -1;
+                                sector_num << 9, 1,
+                                &cluster_offset);
+        if (ret) {
+            return -EINVAL;
         }
         index_in_cluster = sector_num % extent->cluster_sectors;
         n = extent->cluster_sectors - index_in_cluster;
