block: bind FD lifetime of DiskFile

As we can't use BorrowedFd, we should at least create a similar
safe alternative.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

block/src/raw_sync.rs

@@ -10,7 +10,7 @@ use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::DiskTopology;
 
@@ -44,8 +44,8 @@ impl DiskFile for RawFileDiskSync {
         }
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.file.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.file.as_raw_fd())
     }
 }