block: qcow: Implement live resize with L1 table growth

Add support for live resizing QCOW2 images. This enables growing
the virtual size of a QCOW2 disk while the VM is running.

Key features:
- Growing the image automatically expands the L1 table if needed
- Shrinking is not supported
- Resizing for images with backing files is not supported

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

block/src/qcow_sync.rs

@@ -4,7 +4,7 @@
 
 use std::collections::VecDeque;
 use std::fs::File;
-use std::io::{Seek, SeekFrom};
+use std::io::{self, Seek, SeekFrom};
 use std::os::fd::AsRawFd;
 use std::sync::{Arc, Mutex};
 
@@ -68,6 +68,14 @@ impl DiskFile for QcowDiskSync {
         Ok(Box::new(QcowSync::new(Arc::clone(&self.qcow_file))) as Box<dyn AsyncIo>)
     }
 
+    fn resize(&mut self, size: u64) -> DiskFileResult<()> {
+        self.qcow_file
+            .lock()
+            .unwrap()
+            .resize(size)
+            .map_err(|e| DiskFileError::ResizeError(io::Error::other(e)))
+    }
+
     fn fd(&mut self) -> BorrowedDiskFd<'_> {
         BorrowedDiskFd::new(self.qcow_file.lock().unwrap().as_raw_fd())
     }