Re: File Name Case Sensitivity & Globbing! Was: file system name case insensitivity issue: Possible inclusion for the FAQ or User Manual?

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On May 27 16:36, Edward McGuire wrote:
> This note:
> 
> http://cygwin.com/cygwin-ug-net/using-specialnames.html#pathnames-casesensitive
> 
> warns that you cannot have two filenames in the same directory that
> differ only by case, because of NTFS semantics.

No, it does not.  *sigh*

I'm not a native English speaker, but it's still frustrating how my
words are misunderstood.  Read again, now with comment:

  "In the Win32 subsystem filenames are only case-preserved, but not
   case-sensitive."
   
Not NTFS.  The Win32 subsystem.  The underlying native NT calls allow to
specify if the object name is treated case-sensitive or case-insensitive.
The Win32 calls are usually calling their underlying NT pendants with
case-insensitivity switched on.  Therefore you only get a case-insensitive
behaviour on the Win32 surface.
   
   "You can't access two files in the same directory which only differ by
   case,  [...]"

That's just an example.

  "While NTFS (and some remote filesystems) support case-sensitivity, [...]"

Yes, they do.  The NTFS driver is case-sensitive.  This is obviously
used by the POSIX subsystem (Interix/SFU/SUA).  There is *no* reason to
forgo case-sensitivity with NTFS other than:

  "[...] the NT kernel starting with Windows XP does not support it by
   default.  Rather, you have to tweak a registry setting and reboot."

That's the only problem.  This registry settings, if set, lets the NT
kernel ignore all requests for case-sensitive behaviour.  It translates
all calls into case-insensitive calls.  Unless...
   
   "For that reason, case-sensitivity can not be supported by Cygwin,
    unless you change that registry value."

That's it.  Just change a registry value and suddenly case-sensitivity is
enabled in the kernel.  Now you can call native NT functions, request
case-sensitive behaviour, and actually get it.  Now, suddenly you can have
three files called "abc", "Abc and "ABC" in the same directory.  On NTFS:

  $ uname -a
  CYGWIN_NT-6.1 vmbert7 1.7.10(0.241/5/3) 2011-05-27 21:05 i686 Cygwin
  $ echo abc > abc
  $ echo Abc > Abc
  $ echo ABC > ABC
  $ cat abc
  abc
  $ cat Abc
  Abc
  $ cat ABC
  ABC

> It could be improved to warn that because of NTFS semantics there
> are also filenames which exist but which Cygwin's readdir() does not
> return, and which therefore are truly hidden -- will never show up
> in directory listings or globs.

This wouldn't be true.  The problem is not Cygwin's readdir, nor
the underlying OS functions scanning directories.  The only problem is
that non-Cygwin apps, which open one of the above three files, will
always open the same one, regardless whether you specify "abc", "Abc",
or "ABC" as filename.  Because, whatever Cygwin does, or the NT kernel,
the native Win32 applications are *still* case-insensitive.

Did I make myself clear now?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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