[Info-vax] Request description of UFS for VMS person

[Bob Harris]

In article <003954a3$0$14668$c3e8da3 at news.astraweb.com>,
 JF Mezei <jfmezei.spamnot at vaxination.ca> wrote:

> Bob Eager wrote:
> 
> > It isn't the C RTL in my case because I used the open() system call, 
> > rather than fopen(), specifically to exclude that. The check is either 
> > in the kernel (most likely) or in the glue code for open() (highly 
> > unlikely).
> 
> You need to use SYS$OPEN and then SYS$READ :-) :-) :-)
> 
> DOes Unix have the equivalent of SET FILE <mumble> /NODIRECTORY  to
> convert a directory file into a normal file ?

In general no (I write Unix file system code for a living; Tru64, 
HP-UX, Linux, so far).  There may be a Unix implementation that 
has a vendor specific ioctl() that allows something like that, but 
it is not something specified by POSIX nor X/Open.

Officially you are suppose to use calls such as getdirentries(2) 
and readdir(3) to access the contents of a directory.  Opening a 
directory is not a problem (actually it needs to be opened to use 
either of the above calls), however, using read() is "undefined" 
in POSIX and X/Open, where "undefined" means the file system 
implementation is free to do what it wants.

These calls were created partially because some Operating Systems 
(such as OpenVMS) needed a libc way to access directories without 
the application code having to know the actual format of the 
directory.  And because different Unix file systems and/or 
different Unix implementations started creating different 
directory formats.  Eventually Unix file systems moved beyond flat 
directories and starting using fast lookup technologies.  For 
example Tru64 Unix AdvFS used a form of b-trees.

                                        Bob Harris