Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!uunet!microsoft!alistair
From: alistair@microsoft.UUCP (Alistair BANKS)
Newsgroups: comp.os.os2
Subject: Re: Extended attributes on 1.2
Message-ID: <55865@microsoft.UUCP>
Date: 16 Jul 90 23:29:55 GMT
References: <20851.267aadeb@zodiac.ukc.ac.uk>
Reply-To: alistair@microsoft.UUCP (Alistair BANKS)
Organization: Microsoft Corp., Redmond WA
Lines: 36

OS/2 does not 'add extended attributes' as a capability
to a disk. Extended Attributes are down-compatible
with the DOS FAT format - OS/2 Creates them as needed on
any FAT disk and they are invisible to DOS programs.

To understand this you should realise that EAs owned by a
file or directory on a FAT disk are physically stored in
disk space owned by the hidden, system, read-only file
stored in the root called "EA DATA. SF". The EA data is
pointed to by reserved bytes in the FAT directory entry
structure. This file should never be manipulated directly.
You should use the EA APIs in the OS/2 1.2 toolkit. You may
be able to reverse-engineer the mechanism by careful use of
a disk sector editor, though the actual format remains
unpublished for the time-being.

This weird file has to exist to ensure total down-level
compatibility. Its name is valid, although very unlikely
to be chosen by any previous application.

So no installation step is needed. OS/2 will create the EAs
and the "EA DATA. SF" file as needed. If you use DOS to
delete a file that OS/2 has attached EAs to, then OS2
chkdsk will recognise that those EAs have not been deleted.
Never use DOS to delete "EA DATA. SF" or you will have
deleted all those EAs OS/2 created for you.

DOS file deletion is not a disaster, it just might waste 
some small disk space. Every now-and-then, in this case, 
you should run the OS/2 chkdsk, having booted from the OS/2 
install diskette, to 'unlock' your C drive, and then 
chkdsk/f to regain the 'lost' EA space on FAT disks.

Alistair Banks
OS/2 ISV Group
Microsoft