block/null: Implement bdrv_get_allocated_file_size

It is trivial, so we might as well do it.

Remove _filter_actual_image_size from iotest 184, so we get to see the
result in its reference output.

Signed-off-by: Max Reitz <mreitz@redhat.com>

block/null.c

@@ -262,6 +262,11 @@ static void null_refresh_filename(BlockDriverState *bs)
              bs->drv->format_name);
 }
 
+static int64_t null_allocated_file_size(BlockDriverState *bs)
+{
+    return 0;
+}
+
 static const char *const null_strong_runtime_opts[] = {
     BLOCK_OPT_SIZE,
     NULL_OPT_ZEROES,
@@ -277,6 +282,7 @@ static BlockDriver bdrv_null_co = {
     .bdrv_file_open         = null_file_open,
     .bdrv_parse_filename    = null_co_parse_filename,
     .bdrv_getlength         = null_getlength,
+    .bdrv_get_allocated_file_size = null_allocated_file_size,
 
     .bdrv_co_preadv         = null_co_preadv,
     .bdrv_co_pwritev        = null_co_pwritev,
@@ -297,6 +303,7 @@ static BlockDriver bdrv_null_aio = {
     .bdrv_file_open         = null_file_open,
     .bdrv_parse_filename    = null_aio_parse_filename,
     .bdrv_getlength         = null_getlength,
+    .bdrv_get_allocated_file_size = null_allocated_file_size,
 
     .bdrv_aio_preadv        = null_aio_preadv,
     .bdrv_aio_pwritev       = null_aio_pwritev,

tests/qemu-iotests/153.out

@@ -464,7 +464,7 @@ No conflict:
 image: null-co://
 file format: null-co
 virtual size: 1 GiB (1073741824 bytes)
-disk size: unavailable
+disk size: 0 B
 
 Conflict:
 qemu-img: --force-share/-U conflicts with image options

tests/qemu-iotests/184

@@ -45,8 +45,7 @@ do_run_qemu()
 run_qemu()
 {
     do_run_qemu "$@" 2>&1 | _filter_testdir | _filter_qemu | _filter_qmp\
-                          | _filter_qemu_io | _filter_generated_node_ids \
-                          | _filter_actual_image_size
+                          | _filter_qemu_io | _filter_generated_node_ids
 }
 
 test_throttle=$($QEMU_IMG --help|grep throttle)

tests/qemu-iotests/184.out

@@ -29,7 +29,8 @@ Testing:
             "image": {
                 "virtual-size": 1073741824,
                 "filename": "json:{\"throttle-group\": \"group0\", \"driver\": \"throttle\", \"file\": {\"driver\": \"null-co\"}}",
-                "format": "throttle"
+                "format": "throttle",
+                "actual-size": 0
             },
             "iops_wr": 0,
             "ro": false,
@@ -56,7 +57,8 @@ Testing:
             "image": {
                 "virtual-size": 1073741824,
                 "filename": "null-co://",
-                "format": "null-co"
+                "format": "null-co",
+                "actual-size": 0
             },
             "iops_wr": 0,
             "ro": false,