Re: how to check for dirent.d_type support from shell, python or perl?

[Pádraig Brady]

On 12/05/11 17:41, Jim Meyering wrote:
> I'd like to skip my new strace-vs-ls --color test on any
> system (OS and/or file system) that lacks dirent.d_type support.
> Ideally, it'd be a tiny bourne shell, python or perl script
> to tell me if calling readdir on a given directory (let's say ".")
> would provide struct dirent data including usable d_type values.
> [For reference, some file system types do not support that, e.g.,
> reiser3 and xfs, while others do, like ext4 and tmpfs. ]
> 
> Unfortunately, so far it appears there is no way to get to
> the d_type member from any of those languages.
> 
> Does anyone know a way that does not require compiling
> and running a C program?
> 
> I though strace -v might help, but e.g., strace -v ls empty-dir shows
> only the getdents syscalls.  No details about readdir-returned data.

Something based on this might work?


#!/usr/bin/python

# Return status indicates if d_type returned

import ctypes
import sys

(DT_UNKNOWN, DT_DIR,) = (0, 4,)

class dirent(ctypes.Structure):
  _fields_ = [
    ("d_ino", ctypes.c_long),
    ("d_off", ctypes.c_long),
    ("d_reclen", ctypes.c_ushort),
    ("d_type", ctypes.c_ubyte),
    ("d_name", ctypes.c_char*256)]

direntp = ctypes.POINTER(dirent)

libc = ctypes.cdll.LoadLibrary("libc.so.6")
libc.readdir.restype = direntp

dirp = libc.opendir(".")
if dirp:
  ep = libc.readdir(dirp)
else:
  sys.exit(1)

sys.exit(ep.contents.d_type != DT_DIR)