Add remove_pseudo_root option to remove all inode when umount

In order to make the hot upgrade of virtiofs easy, VFS will save pseudo
inodes when umount for easy recovery. However, in the fuse scenario, if
umount does not remove the pseudo inode, it will cause an invalid
directory to be seen on the host, which is not friendly to users. So add
this option to control this behavior.

Signed-off-by: zyfjeff <zyfjeff@linux.alibaba.com>

Author: zyfjeff

src/api/vfs/mod.rs

@@ -292,6 +292,7 @@ pub struct Vfs {
     opts: ArcSwap<VfsOptions>,
     initialized: AtomicBool,
     lock: Mutex<()>,
+    remove_pseudo_root: bool,
 }
 
 impl Default for Vfs {
@@ -311,9 +312,15 @@ impl Vfs {
             opts: ArcSwap::new(Arc::new(opts)),
             lock: Mutex::new(()),
             initialized: AtomicBool::new(false),
+            remove_pseudo_root: false,
         }
     }
 
+    /// mark remove pseudo root inode when umount
+    pub fn set_remove_pseudo_root(&mut self) {
+        self.remove_pseudo_root = true;
+    }
+
     /// For sake of live-upgrade, only after negotiation is done, it's safe to persist
     /// state of vfs.
     pub fn initialized(&self) -> bool {
@@ -406,7 +413,14 @@ impl Vfs {
                 // 1. they can be reused later on
                 // 2. during live upgrade, it is easier reconstruct pseudofs inodes since
                 //    we do not have to track pseudofs deletions
-                //self.root.evict_inode(inode);
+                // In order to make the hot upgrade of virtiofs easy, VFS will save pseudo
+                // inodes when umount for easy recovery. However, in the fuse scenario, if
+                // umount does not remove the pseudo inode, it will cause an invalid
+                // directory to be seen on the host, which is not friendly to users. So add
+                // this option to control this behavior.
+                if self.remove_pseudo_root {
+                    self.root.evict_inode(inode);
+                }
                 mountpoints.remove(&inode);
                 self.mountpoints.store(Arc::new(mountpoints));
                 x.fs_idx