block: Simplify AsyncAdaptor

It shouldn't be necessary to lock the file for the adaptor. This removes
two layers of indirection for QcowDiskSync and VhdxDiskSync.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

block/src/vhdx_sync.rs

@@ -5,7 +5,6 @@
 use std::collections::VecDeque;
 use std::fs::File;
 use std::os::fd::AsRawFd;
-use std::sync::{Arc, Mutex, MutexGuard};
 
 use vmm_sys_util::eventfd::EventFd;
 
@@ -16,20 +15,20 @@ use crate::vhdx::{Result as VhdxResult, Vhdx};
 use crate::AsyncAdaptor;
 
 pub struct VhdxDiskSync {
-    vhdx_file: Arc<Mutex<Vhdx>>,
+    vhdx_file: Vhdx,
 }
 
 impl VhdxDiskSync {
     pub fn new(f: File) -> VhdxResult<Self> {
         Ok(VhdxDiskSync {
-            vhdx_file: Arc::new(Mutex::new(Vhdx::new(f)?)),
+            vhdx_file: Vhdx::new(f)?,
         })
     }
 }
 
 impl DiskFile for VhdxDiskSync {
     fn size(&mut self) -> DiskFileResult<u64> {
-        Ok(self.vhdx_file.lock().unwrap().virtual_disk_size())
+        Ok(self.vhdx_file.virtual_disk_size())
     }
 
     fn new_async_io(&self, _ring_depth: u32) -> DiskFileResult<Box<dyn AsyncIo>> {
@@ -40,19 +39,18 @@ impl DiskFile for VhdxDiskSync {
     }
 
     fn fd(&mut self) -> BorrowedDiskFd<'_> {
-        let lock = self.vhdx_file.lock().unwrap();
-        BorrowedDiskFd::new(lock.as_raw_fd())
+        BorrowedDiskFd::new(self.vhdx_file.as_raw_fd())
     }
 }
 
 pub struct VhdxSync {
-    vhdx_file: Arc<Mutex<Vhdx>>,
+    vhdx_file: Vhdx,
     eventfd: EventFd,
     completion_list: VecDeque<(u64, i32)>,
 }
 
 impl VhdxSync {
-    pub fn new(vhdx_file: Arc<Mutex<Vhdx>>) -> std::io::Result<Self> {
+    pub fn new(vhdx_file: Vhdx) -> std::io::Result<Self> {
         Ok(VhdxSync {
             vhdx_file,
             eventfd: EventFd::new(libc::EFD_NONBLOCK)?,
@@ -61,11 +59,7 @@ impl VhdxSync {
     }
 }
 
-impl AsyncAdaptor<Vhdx> for Arc<Mutex<Vhdx>> {
-    fn file(&mut self) -> MutexGuard<'_, Vhdx> {
-        self.lock().unwrap()
-    }
-}
+impl AsyncAdaptor for Vhdx {}
 
 impl AsyncIo for VhdxSync {
     fn notifier(&self) -> &EventFd {