block: enable to get a raw FD of each block device's DiskFile

This is a prerequisite for the next steps.

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

block/src/qcow/mod.rs

@@ -13,6 +13,7 @@ use std::cmp::{max, min};
 use std::fs::OpenOptions;
 use std::io::{self, Read, Seek, SeekFrom, Write};
 use std::mem::size_of;
+use std::os::fd::{AsRawFd, RawFd};
 use std::str;
 
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
@@ -1516,6 +1517,12 @@ impl QcowFile {
     }
 }
 
+impl AsRawFd for QcowFile {
+    fn as_raw_fd(&self) -> RawFd {
+        self.raw_file.as_raw_fd()
+    }
+}
+
 impl Drop for QcowFile {
     fn drop(&mut self) {
         let _ = self.sync_caches();

block/src/qcow/qcow_raw_file.rs

@@ -6,6 +6,7 @@
 
 use std::io::{self, BufWriter, Seek, SeekFrom, Write};
 use std::mem::size_of;
+use std::os::fd::{AsRawFd, RawFd};
 
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
 use vmm_sys_util::write_zeroes::WriteZeroes;
@@ -159,3 +160,9 @@ impl Clone for QcowRawFile {
         }
     }
 }
+
+impl AsRawFd for QcowRawFile {
+    fn as_raw_fd(&self) -> RawFd {
+        self.file.as_raw_fd()
+    }
+}

block/src/qcow/raw_file.rs

@@ -369,3 +369,9 @@ impl Clone for RawFile {
         }
     }
 }
+
+impl AsRawFd for RawFile {
+    fn as_raw_fd(&self) -> RawFd {
+        self.file.as_raw_fd()
+    }
+}