cifs: add a function to get a cached dir based on its dentry

Needed for subsequent patches in the directory caching
series.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -925,6 +925,22 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	return rc;
 }
 
+int open_cached_dir_by_dentry(struct cifs_tcon *tcon,
+			      struct dentry *dentry,
+			      struct cached_fid **cfid)
+{
+	mutex_lock(&tcon->crfid.fid_mutex);
+	if (tcon->crfid.dentry == dentry) {
+		cifs_dbg(FYI, "found a cached root file handle by dentry\n");
+		*cfid = &tcon->crfid;
+		kref_get(&tcon->crfid.refcount);
+		mutex_unlock(&tcon->crfid.fid_mutex);
+		return 0;
+	}
+	mutex_unlock(&tcon->crfid.fid_mutex);
+	return -ENOENT;
+}
+
 static void
 smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon,
 	      struct cifs_sb_info *cifs_sb)

fs/cifs/smb2proto.h

@@ -73,6 +73,9 @@ extern int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 			   const char *path,
 			   struct cifs_sb_info *cifs_sb,
 			   struct cached_fid **cfid);
+extern int open_cached_dir_by_dentry(struct cifs_tcon *tcon,
+				     struct dentry *dentry,
+				     struct cached_fid **cfid);
 extern void close_cached_dir(struct cached_fid *cfid);
 extern void close_cached_dir_lease(struct cached_fid *cfid);
 extern void close_cached_dir_lease_locked(struct cached_fid *cfid);