vmdk: Fix backing file handling

Instead of storing the backing file in its own BlockDriverState, VMDK uses the
BlockDriverState of the raw image file it opened. This is wrong and breaks
functions that access the backing file or protocols. This fix replaces all
occurrences of s->hd->backing_* with bs->backing_*.

This fixes qemu-iotests failure in 020 (Commit changes to backing file).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Glauber Costa <glommer@redhat.com>

block-vmdk.c

@@ -169,7 +169,7 @@ static int vmdk_is_cid_valid(BlockDriverState *bs)
 {
 #ifdef CHECK_CID
     BDRVVmdkState *s = bs->opaque;
-    BlockDriverState *p_bs = s->hd->backing_hd;
+    BlockDriverState *p_bs = bs->backing_hd;
     uint32_t cur_pcid;
 
     if (p_bs) {
@@ -337,26 +337,26 @@ static int vmdk_parent_open(BlockDriverState *bs, const char * filename)
         p_name += sizeof("parentFileNameHint") + 1;
         if ((end_name = strchr(p_name,'\"')) == 0)
             return -1;
-        if ((end_name - p_name) > sizeof (s->hd->backing_file) - 1)
+        if ((end_name - p_name) > sizeof (bs->backing_file) - 1)
             return -1;
 
-        pstrcpy(s->hd->backing_file, end_name - p_name + 1, p_name);
-        if (stat(s->hd->backing_file, &file_buf) != 0) {
+        pstrcpy(bs->backing_file, end_name - p_name + 1, p_name);
+        if (stat(bs->backing_file, &file_buf) != 0) {
             path_combine(parent_img_name, sizeof(parent_img_name),
-                         filename, s->hd->backing_file);
+                         filename, bs->backing_file);
         } else {
             pstrcpy(parent_img_name, sizeof(parent_img_name),
-                    s->hd->backing_file);
+                    bs->backing_file);
         }
 
-        s->hd->backing_hd = bdrv_new("");
-        if (!s->hd->backing_hd) {
+        bs->backing_hd = bdrv_new("");
+        if (!bs->backing_hd) {
             failure:
             bdrv_close(s->hd);
             return -1;
         }
         parent_open = 1;
-        if (bdrv_open(s->hd->backing_hd, parent_img_name, BDRV_O_RDONLY) < 0)
+        if (bdrv_open(bs->backing_hd, parent_img_name, BDRV_O_RDONLY) < 0)
             goto failure;
         parent_open = 0;
     }
@@ -463,13 +463,14 @@ static int get_whole_cluster(BlockDriverState *bs, uint64_t cluster_offset,
 
     // we will be here if it's first write on non-exist grain(cluster).
     // try to read from parent image, if exist
-    if (s->hd->backing_hd) {
-        BDRVVmdkState *ps = s->hd->backing_hd->opaque;
+    if (bs->backing_hd) {
+        BDRVVmdkState *ps = bs->backing_hd->opaque;
 
         if (!vmdk_is_cid_valid(bs))
             return -1;
 
-        parent_cluster_offset = get_cluster_offset(s->hd->backing_hd, NULL, offset, allocate);
+        parent_cluster_offset = get_cluster_offset(bs->backing_hd, NULL,
+            offset, allocate);
 
         if (parent_cluster_offset) {
             BDRVVmdkState *act_s = activeBDRV.hd->opaque;
@@ -620,10 +621,10 @@ static int vmdk_read(BlockDriverState *bs, int64_t sector_num,
             n = nb_sectors;
         if (!cluster_offset) {
             // try to read from parent image, if exist
-            if (s->hd->backing_hd) {
+            if (bs->backing_hd) {
                 if (!vmdk_is_cid_valid(bs))
                     return -1;
-                ret = bdrv_read(s->hd->backing_hd, sector_num, buf, n);
+                ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
                 if (ret < 0)
                     return -1;
             } else {