tests: fix dirent d_type support verification

* init.cfg (require_dirent_d_type_): Don't use df -x
to exclude XFS, since this depends on a correct mtab
which is brittle and often not correct within chroots.
* tests/d_type-check: Check also the d_type of files,
which excludes XFS appropriately.  Specify all argument
and return types to avoid truncated pointers being passed,
which skipped the test due to crashes on x86_64 at least.
Simplify the C library lookup by reusing the interpreter's.

chroot issue reported at https://bugzilla.redhat.com/1263341

init.cfg

@@ -488,12 +488,6 @@ require_dirent_d_type_()
   python < /dev/null \
     || skip_ python missing: assuming no d_type support
 
-  # Manually exclude xfs, since the test would mistakenly report
-  # that it has d_type support: d_type == DT_DIR for "." and "..",
-  # but DT_UNKNOWN for all other types.
-  df -x xfs . > /dev/null 2>&1 \
-    || skip_ requires d_type support
-
   python "$abs_srcdir"/tests/d_type-check \
     || skip_ requires d_type support
 }

tests/d_type-check

@@ -1,13 +1,17 @@
 #!/usr/bin/python
-# Exit 0 if "." has useful d_type information, else 1.
+# Exit 0 if "." and "./tempfile" have useful d_type information, else 1.
 # Intended to exit 0 only on Linux/GNU systems.
+import os
 import sys
+import tempfile
 
 fail = 1
+fname = None
+
 try:
   import ctypes.util
 
-  (DT_UNKNOWN, DT_DIR,) = (0, 4,)
+  (DT_UNKNOWN, DT_DIR, DT_REG) = (0, 4, 8)
 
   class dirent(ctypes.Structure):
     _fields_ = [
@@ -17,19 +21,48 @@ try:
       ("d_type", ctypes.c_ubyte),
       ("d_name", ctypes.c_char*256)]
 
+  # Pass NULL to dlopen, assuming the python
+  # interpreter is linked with the C runtime
+  libc = ctypes.CDLL(None)
+
+  # Setup correct types for all args and returns
+  # even if only passing, to avoid truncation etc.
+  dirp = ctypes.c_void_p
   direntp = ctypes.POINTER(dirent)
 
-  libc = ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
+  libc.readdir.argtypes = [dirp]
   libc.readdir.restype = direntp
 
+  libc.opendir.restype = dirp
+
+  # Ensure a file is present
+  f, fname = tempfile.mkstemp(dir='.')
+  fname = os.path.basename(fname)
+
   dirp = libc.opendir(".")
   if dirp:
-    ep = libc.readdir(dirp)
-    if ep:
+    while True:
+      ep = libc.readdir(dirp)
+      if not ep: break
+      d_type = ep.contents.d_type
       name = ep.contents.d_name
-      if (name == "." or name == "..") and ep.contents.d_type == DT_DIR:
+      if name == "." or name == "..":
+        if d_type != DT_DIR: break
+      # Check files too since on XFS, only dirs have DT_DIR
+      # while everything else has DT_UNKNOWN
+      elif name == fname:
+        if d_type == DT_REG:
+          fail = 0
+        break
+      elif d_type != DT_DIR and d_type != DT_UNKNOWN:
         fail = 0
+        break
+except:
+  pass
 
+try:
+  if fname:
+    os.unlink(fname);
 except:
   pass