File ioemu-tapdisk-compat-QEMU_IMG.patch of Package xen

tapdisk-ioemu should compat to QMEU_IMG, or use tapdisk as backend 
will fail to boot tap:vmdk image.

Index: xen-3.3.1-testing/tools/ioemu-remote/block.c
===================================================================
--- xen-3.3.1-testing.orig/tools/ioemu-remote/block.c
+++ xen-3.3.1-testing/tools/ioemu-remote/block.c
@@ -1255,7 +1255,10 @@ static BlockDriverAIOCB *bdrv_aio_read_e
     int ret;
     ret = bdrv_read(bs, sector_num, buf, nb_sectors);
     cb(opaque, ret);
-    return NULL;
+    if (ret != 0)
+        return NULL;
+    else
+        return (BlockDriverAIOCB *)1;
 }
 
 static BlockDriverAIOCB *bdrv_aio_write_em(BlockDriverState *bs,
@@ -1265,7 +1268,10 @@ static BlockDriverAIOCB *bdrv_aio_write_
     int ret;
     ret = bdrv_write(bs, sector_num, buf, nb_sectors);
     cb(opaque, ret);
-    return NULL;
+    if (ret != 0)
+        return NULL;
+    else
+        return (BlockDriverAIOCB *)1;
 }
 
 static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
@@ -1274,7 +1280,10 @@ static BlockDriverAIOCB *bdrv_aio_flush_
     int ret;
     ret = bdrv_flush(bs);
     cb(opaque, ret);
-    return NULL;
+    if (ret != 0)
+        return NULL;
+    else
+        return (BlockDriverAIOCB *)1;
 }
 
 static void bdrv_aio_cancel_em(BlockDriverAIOCB *acb)