block: Add punch_hole and write_zeroes to AsyncIo trait

Add punch_hole() and write_zeroes() methods to the AsyncIo trait
with stub implementations for all backends. These will be used to
support DISCARD and WRITE_ZEROES operations.

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

block/src/qcow_sync.rs

@@ -11,7 +11,7 @@ use std::sync::{Arc, Mutex};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::qcow::{QcowFile, RawFile, Result as QcowResult};
 use crate::{AsyncAdaptor, BlockBackend};
@@ -146,4 +146,16 @@ impl AsyncIo for QcowSync {
     fn next_completed_request(&mut self) -> Option<(u64, i32)> {
         self.completion_list.pop_front()
     }
+
+    fn punch_hole(&mut self, _offset: u64, _length: u64, _user_data: u64) -> AsyncIoResult<()> {
+        Err(AsyncIoError::PunchHole(std::io::Error::other(
+            "punch_hole not supported for QCOW sync backend",
+        )))
+    }
+
+    fn write_zeroes(&mut self, _offset: u64, _length: u64, _user_data: u64) -> AsyncIoResult<()> {
+        Err(AsyncIoError::WriteZeroes(std::io::Error::other(
+            "write_zeroes not supported for QCOW sync backend",
+        )))
+    }
 }