--- a/mercurial/cffi/osutil.py	Sun Oct 06 09:45:02 2019 -0400
+++ b/mercurial/cffi/osutil.py	Sun Oct 06 09:48:39 2019 -0400
@@ -40,8 +40,8 @@
             self.st_mtime = st_mtime
             self.st_size = st_size
 
-    tv_sec_ofs = ffi.offsetof("struct timespec", "tv_sec")
-    buf = ffi.new("char[]", listdir_batch_size)
+    tv_sec_ofs = ffi.offsetof(b"struct timespec", b"tv_sec")
+    buf = ffi.new(b"char[]", listdir_batch_size)
 
     def listdirinternal(dfd, req, stat, skip):
         ret = []
@@ -51,20 +51,20 @@
                 break
             if r == -1:
                 raise OSError(ffi.errno, os.strerror(ffi.errno))
-            cur = ffi.cast("val_attrs_t*", buf)
+            cur = ffi.cast(b"val_attrs_t*", buf)
             for i in range(r):
                 lgt = cur.length
-                assert lgt == ffi.cast('uint32_t*', cur)[0]
+                assert lgt == ffi.cast(b'uint32_t*', cur)[0]
                 ofs = cur.name_info.attr_dataoffset
                 str_lgt = cur.name_info.attr_length
-                base_ofs = ffi.offsetof('val_attrs_t', 'name_info')
+                base_ofs = ffi.offsetof(b'val_attrs_t', b'name_info')
                 name = str(
                     ffi.buffer(
-                        ffi.cast("char*", cur) + base_ofs + ofs, str_lgt - 1
+                        ffi.cast(b"char*", cur) + base_ofs + ofs, str_lgt - 1
                     )
                 )
                 tp = attrkinds[cur.obj_type]
-                if name == "." or name == "..":
+                if name == b"." or name == b"..":
                     continue
                 if skip == name and tp == statmod.S_ISDIR:
                     return []
@@ -85,12 +85,12 @@
                 else:
                     ret.append((name, tp))
                 cur = ffi.cast(
-                    "val_attrs_t*", int(ffi.cast("intptr_t", cur)) + lgt
+                    b"val_attrs_t*", int(ffi.cast(b"intptr_t", cur)) + lgt
                 )
         return ret
 
     def listdir(path, stat=False, skip=None):
-        req = ffi.new("struct attrlist*")
+        req = ffi.new(b"struct attrlist*")
         req.bitmapcount = lib.ATTR_BIT_MAP_COUNT
         req.commonattr = (
             lib.ATTR_CMN_RETURNED_ATTRS