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SubjectRe: ext2(3?) streams application
   Date: 	Sun, 16 May 1999 17:39:03 +0200
From: Rolf Fokkens <rolf@flits102-126.flits.rug.nl>

I recently read about the streams facility in NTFS. I searched the
internet (not very thoroughly) to see if these streams would be
considered for linux. I didn't find very much info about it, except that
they wouldn't fit in the unix file interface.

It's more than just that it doesn't fit in the Unix file interface. It
also presents problems for a large number of internet protocols, such as
FTP and HTTP as well. One of the real annoyances of the Macintosh was
that you couldn't just ftp files around without trashing the resource
fork. You had to binhex them first, which was a real pain to say the
least.

I do see some internal applications for streames though within the ext2
(or ext3 or whatever) filesystem, which might be of use. I'll mention
them:
1) ext2compr: Compressed files need a bitmap telling which blocks are
compressed. A separate stream for this might be handy.
2) ACL: Access Control Lists might use a separate stream
3) Capabilities: I hardly know anything about capabilities, but I assume
they need some adminsitration. This might be done in a separate stream.

Some of these may be useful additional file metadata which is stored by
the kernel, and administered by the kernel. A generic mechanism for
storing such items may very well be useful, although these items are
small and only need to be accessed and modified by the kernel. (Indeed,
for ACL's and Capabilities, you only want the kernel mucking with them
for security reasons!)

But that is a very different beast than the streams facility in NTFS,
where user-level programs have access to the streams. If you are
designing an application progam and you need that kind of facility,
you're probably better off inventing your own internal file structure to
store the streams, since at least that way the file can be safely ftp'ed
and accessed over NFS. Alternatively, you could put all of the
information into seprate files in a directory, which is the approach
NeXTStep used instead of the diastrous resource fork approach used by
the Macintosh.

- Ted

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