Re: Platform portable support of heir. file systems

[kilgallen@eisner.decus.org (Larry Kilgallen)]

s In article <dewar.851276907@merv>, dewar@merv.cs.nyu.edu (Robert Dewar) writes:
> Larry said
> 
> "Even though we might all _wish_ there was an easy answer,
> wishing does not make it so.  Posix provides an approach
> for those running under Unix-emulating subsystems, including
> MVS Open Edition, but it does not provide transparent access
> to the bulk of existing data on non-Unix systems. I do not
> mean to slight the Posix committee(s), some tasks are just
> too hard."
> 
> 
> Actually, I think the Posix approach is just fine. Note that you do not
> have to "emulate Unix" to be Posix compliant, just provide a set of
> interfaces (which by the way is certainly not full Unix in any case).
> 
> Manufacturers then make the choice of whether to try to be compliant
> with this standard or not. 

By "emulate Unix", I meant that portion of Unix which must be emulated
to comply with the Posix standards.  Restricting this to a very narrow
area of file name cases (for purposes of discussion), manufacturers of
non-Unix operating systems tend to add a separate file system emulation
in order to be able to support case-sensitive filenames.

In general (VMS Posix, MVS Open Edition) the full Posix user has a
separate little universe for storing and retrieving files, but does
_not_ have the ability to access other files stored according to the
traditions of the operating system in this fashion.  There may be
special utilities to do so, but they are not at all standard between
manufacturers.

This separate-but-compliant approach will work for some application
purposes, but by no means all.  (Consider a program to read all the
traditional files on a system and check for some special trait.)

> So using this apporach you meet half way at an abstract set of 
> interfaces representing a desired set of functionalities. If it is
> possble to map an OS to this interface, then you do so, rather than
> trying to make the top level abstraction handle direcly the quirks
> of every possible operating system.

Yes, and the Posix approach handles some cases well.  I do not
believe going further with a generalized approach would be fruitful.
Those who need os-specific access (including me) will just have to do
os-specific coding.

Larry Kilgallen