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Re: Representing a hierarchical file system

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On Mon, 15 Aug 2011 19:46:03 +0200, jacob navia wrote:

> I would rather ignore links, and avoid anything Unix specific (or DOS
> specific)
> 
> Just a simple hierarchical representation with some attibutes like size
> and time
> 
> I would like it to be as portable as possible

These are self-contradictory.

If you /really/ ignore links then, on Unix, your filesystem will be empty;
a Unix filesystem is nothing but links. A common Unix noob mistake is
asking how to identify or distinguish a hard link (i.e. something created
by link()) from a "real" file. This is a meaningless question; a hard link
is just a directory entry; the links created by "ln" are no different to
those created when the file itself was originally created with open() or
creat().

You can only create a "hierarchical representation" of a Unix filesystem
by losing the distinction between a (hard) link and the file to which it
refers, so you can't distinguish between N links to a single file and N
distinct files. On the bright side, modern Unices don't normally allow
creating hard links to directories, so you can't have cycles (assuming
that you ignore the "." and ".." links).

If you just discard symbolic links, many filenames will simply be invalid
according to your representation, which is likely to impair its utility.
OTOH, if you treat symbolic links as synonymous with the object to which
they refer, not only will your representation not be hierarchical, it will
probably be cyclic (if you actually manage to construct it without going
into infinite recursion).

[Actually, you can end up going into infinite recursion anyhow, if you try
to traverse a directory tree without explicitly checking for loops, as
directories can be renamed (i.e. moved) at any time.]

If you want portability, you really have to support the key features of
all of the target systems (i.e. the common superset, not the common
subset). So e.g. if you want to support Unix, the data model has to
support the concepts of hard and symbolic links. On Windows, these will
still exist as concepts, but you just won't encounter any in practice.

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Thread

Representing a hierarchical file system jacob navia <jacob@spamsink.net> - 2011-08-15 12:24 +0200
  Re: Representing a hierarchical file system Ian Collins <ian-news@hotmail.com> - 2011-08-15 22:36 +1200
    Re: Representing a hierarchical file system jacob navia <jacob@spamsink.net> - 2011-08-15 19:43 +0200
  Re: Representing a hierarchical file system Keith Thompson <kst-u@mib.org> - 2011-08-15 09:23 -0700
    Re: Representing a hierarchical file system David Thompson <dave.thompson2@verizon.net> - 2011-08-21 03:22 -0400
  Re: Representing a hierarchical file system Nobody <nobody@nowhere.com> - 2011-08-15 18:02 +0100
    Re: Representing a hierarchical file system jacob navia <jacob@spamsink.net> - 2011-08-15 19:44 +0200
  Re: Representing a hierarchical file system China Blue Tip Wrench <chine.bleu@yahoo.com> - 2011-08-15 10:35 -0700
    Re: Representing a hierarchical file system jacob navia <jacob@spamsink.net> - 2011-08-15 19:46 +0200
      Re: Representing a hierarchical file system "Heinrich Wolf" <invalid@invalid.invalid> - 2011-08-15 20:31 +0200
      Re: Representing a hierarchical file system Ian Collins <ian-news@hotmail.com> - 2011-08-16 08:32 +1200
      Re: Representing a hierarchical file system Nobody <nobody@nowhere.com> - 2011-08-16 11:45 +0100
        Re: Representing a hierarchical file system BGB <cr88192@hotmail.com> - 2011-08-16 04:00 -0700

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