block: qcow_sync: impl DiskSize for QcowDiskSync

Delegate to QcowMetadata::virtual_size() which returns the guest
visible capacity stored in the QCOW2 header.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/qcow_sync.rs

@@ -15,6 +15,7 @@ use vmm_sys_util::write_zeroes::{PunchHole, WriteZeroesAt};
 use crate::async_io::{
     AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
+use crate::disk_file;
 use crate::error::{BlockError, BlockErrorKind, BlockResult, ErrorOp};
 use crate::qcow::metadata::{
     BackingRead, ClusterReadMapping, ClusterWriteMapping, DeallocAction, QcowMetadata,
@@ -277,6 +278,12 @@ impl Drop for QcowDiskSync {
     }
 }
 
+impl disk_file::DiskSize for QcowDiskSync {
+    fn logical_size(&self) -> BlockResult<u64> {
+        Ok(self.metadata.virtual_size())
+    }
+}
+
 pub struct QcowSync {
     metadata: Arc<QcowMetadata>,
     data_file: QcowRawFile,