commit 5daa74a6ebce7543aaad178c4061dc087bb4c705
author Paolo Bonzini <pbonzini@redhat.com> Wed Sep 04 19:00:38 2013 +0200
committer Stefan Hajnoczi <stefanha@redhat.com> Fri Sep 06 15:25:09 2013 +0200
tree aa338ce4ff4b3549004a3446b2f072bd2e26a2d9
parent 918e92d71b38306a6bf4fedfd1109367f1425587

block: look for zero blocks in bs->file

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block.c

diff --git a/block.c b/block.c
index 3c39769..a325efc 100644
--- a/block.c
+++ b/block.c
@@ -3075,7 +3075,7 @@
 {
     int64_t length;
     int64_t n;
-    int64_t ret;
+    int64_t ret, ret2;
 
     length = bdrv_getlength(bs);
     if (length < 0) {
@@ -3117,6 +3117,20 @@
             }
         }
     }
+
+    if (bs->file &&
+        (ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO) &&
+        (ret & BDRV_BLOCK_OFFSET_VALID)) {
+        ret2 = bdrv_co_get_block_status(bs->file, ret >> BDRV_SECTOR_BITS,
+                                        *pnum, pnum);
+        if (ret2 >= 0) {
+            /* Ignore errors.  This is just providing extra information, it
+             * is useful but not necessary.
+             */
+            ret |= (ret2 & BDRV_BLOCK_ZERO);
+        }
+    }
+
     return ret;
 }