[PULL v2 6/9] parallels: skip loading a genuinely empty bitmap L1 table

parallels_load_bitmap_data() unconditionally calls
bdrv_dirty_bitmap_deserialize_finish() even when there is nothing to
deserialize, which hits an assertion in hbitmap
(hbitmap_iter_init: 'pos < hb->size') when the bitmap itself has
zero size, i.e. the disk is a zero-sector image.

Skip allocating, populating and loading the L1 table entirely when
l1_size == 0. This is safe only because the previous commit already
guarantees l1_size == 0 exclusively means the disk has 0 size.

Signed-off-by: Denis V. Lunev <[email protected]>
CC: Thomas Huth <[email protected]>
CC: Stefan Hajnoczi <[email protected]>
---
 block/parallels-ext.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/block/parallels-ext.c b/block/parallels-ext.c
index 97744c9696..704e16e1de 100644
--- a/block/parallels-ext.c
+++ b/block/parallels-ext.c
@@ -168,14 +168,17 @@ parallels_load_bitmap(BlockDriverState *bs, uint8_t *data, size_t data_size,
         goto fail;
     }
 
-    l1_table = g_new(uint64_t, bf.l1_size);
-    for (i = 0; i < bf.l1_size; i++, data += sizeof(uint64_t)) {
-        l1_table[i] = ldq_le_p(data);
-    }
+    if (bf.l1_size != 0) {
+        l1_table = g_new(uint64_t, bf.l1_size);
+        for (i = 0; i < bf.l1_size; i++, data += sizeof(uint64_t)) {
+            l1_table[i] = ldq_le_p(data);
+        }
 
-    ret = parallels_load_bitmap_data(bs, l1_table, bf.l1_size, bitmap, errp);
-    if (ret < 0) {
-        goto fail;
+        ret = parallels_load_bitmap_data(bs, l1_table, bf.l1_size, bitmap,
+                                         errp);
+        if (ret < 0) {
+            goto fail;
+        }
     }
 
     /* We support format extension only for RO parallels images. */
-- 
2.53.0