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From: johnson@noscvax.UUCP (Timothy A. Johnson)
Newsgroups: net.micro.pc
Subject: Re: MS-DOS function 4Eh problem!
Message-ID: <1084@noscvax.UUCP>
Date: Mon, 26-Aug-85 17:49:48 EDT
Article-I.D.: noscvax.1084
Posted: Mon Aug 26 17:49:48 1985
Date-Received: Sat, 31-Aug-85 04:47:52 EDT
References: <1106@pucc-i> <2388@watcgl.UUCP>
Organization: Naval Ocean Systems Center, San Diego
Lines: 34

>
> 	I am writing a program in which, among other things, I would like to
> be able to read (and set or alter) disk's Volume-ID label.  I was hoping that
> I could use MS-DOS function call 4Eh to obtain the v-id label with attribute
> byte set to 08 and the pathname set to *.*.  To my surprise, 4E would return
> the file name (and the rest) of the first file on the disk regardless of the 
> file attribute.  In fact it seems that 4E function does not try to mach file
> attribute as it is documented in the MS-DOS manual since most files have the
> byte attribute of 20h and no matter to what value the CX register is set, 4E 
> only maches the pathname.
> 
> 	Am I not interpreting documentation correctly or is this a bug?  BTW,
> program is written in Turbo Pascal 3.0 and running on Pronto Series 16 with
> MS-DOS 2.0.  Also, I am aware of the alternate ways to do it (use absolute
> disk read interrupt 25h  to get the directory sectors and manipulate them
> "manually").
>

I have come across this problem, also. I believe it is a bug in DOS versions
prior to 3.0 (or at least 3.1). Calling function 4EH with *.* or ????????.???
and the attribute mask of 8 is correct. However, if the label happens to be
the first non-deleted directory entry (in the root, of course), it will not
be found. The function works as expected when at least one non-deleted file
entry exists in the directory prior to the label entry. I found this to be
true on both a Zenith Z-150 under MS-DOS 2.11 and an IBM PC under PC-DOS 2.1.
When I tried the same program with an IBM PC and PC-DOS 3.1, it always found
the label no matter where it was in the root directory.

BTW: I suspect that using '*' as the file name mask is not sufficient since
the label can have up to 11 characters and trailing three characters are stored
in the same place as a normal file's extension.

Tim Johnson
Computer Sciences Corporation