Path: utzoo!attcan!uunet!portal!cup.portal.com!Robert_C_Tellefson
From: Robert_C_Tellefson@cup.portal.com
Newsgroups: comp.sys.ibm.pc
Subject: Re: How do I open() DOS directories?
Message-ID: <6015@cup.portal.com>
Date: 28 May 88 18:26:02 GMT
References: <221@h-three.UUCP> <5631@cup.portal.com> <907@parcvax.Xerox.COM> <121@chiron.UUCP>
Organization: The Portal System (TM)
Lines: 53
XPortal-User-Id: 1.1001.2624

It seems I jumped to an invalid conclusion based on a reasonable
assumption - easy to do when working with DOS.

My company produces a hard disk manager and DOS shell called JOBS
(an acronym for Job Organization and Backup System).  We use FCB's to
create/rename disk volume labels and to rename directories.  These
functions can not be accomplished using DOS file handles.

Examples:

    We create a disk label by creating a file with a volume label
    attribute and then close it (using DOS functions 16h & 10h).  

    We rename directories using FCB's and function 17h.  

These old FCB functions are the only way to perform these operations in a
DOS compatible way, IE., directories can not be renamed using the Change
Directory Entry function (56h).

My error was to assume that DOS would support the other FCB functions as
well.  After these many years with DOS, I should know better than to
assume anything.

I tested the other function calls and it seems none of the other FCB
functions can be applied to a directory entry with an attribute of 10h,
the attribute given to subdirectories.  

Directories are just files allocated space one cluster at a time.  With
proper DOS support they could be read into memory and treated as ordinary
data.  As it is, the only way to accomplish this is to use interrupts 25h &
26h (absolute disk read/write) to get a directory's cluster assignment
and then translate (using the File Allocation Table) to a physical
cluster address followed by an absolute disk read of that cluster or
possibly clusters.

Int 25h & 26h access is used by a number of popular disk managers.  I
agree with Jon L. Griffeth when he says that is unwise to go around
DOS to access directories directly.  JOBS is 100% DOS & BIOS compatible
and one benefit of that is its ability to be used on Unix partitions
(under DOS-merge or the like) without modification.  Try that with Qdos
or other programs that use direct knowledge of a disk's layout!

Information about JOBS' Sharware version and JOBS+ (not Shareware) is
available upon request.

Bob Tellefson                    uucp:  tellefson@cup.portal.com
RCT Design                 Compuserve:  73417,545
                                Genie:  R.TELLEFSON
                                Voice:  (408) 749-9826
                                 USPS:  663 S. Bernardo #7
                                        Sunnyvale, CA 94087
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        I began with nothing and I still have most of it.