vm-virtio: Implement shutdown() for virtio-fs

Since the virtio-fs device is backed by a vhost-user process, it is
important to implement the proper shutdown() function from the
VirtioDevice trait, as vhost-user-blk and vhost-user-net do.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-virtio/src/vhost_user/fs.rs

@@ -13,7 +13,7 @@ use libc::{self, c_void, off64_t, pread64, pwrite64, EFD_NONBLOCK};
 use std::cmp;
 use std::io;
 use std::io::Write;
-use std::os::unix::io::RawFd;
+use std::os::unix::io::{AsRawFd, RawFd};
 use std::result;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
@@ -544,6 +544,10 @@ impl VirtioDevice for Fs {
         ))
     }
 
+    fn shutdown(&mut self) {
+        let _ = unsafe { libc::close(self.vu.as_raw_fd()) };
+    }
+
     fn get_shm_regions(&self) -> Option<VirtioSharedMemoryList> {
         if let Some(cache) = self.cache.as_ref() {
             Some(cache.0.clone())