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SubjectRe: Implementing Meta File information in Linux
On Tue, 1 Sep 1998, Stephen C. Tweedie wrote:

> The issue was about adding extra streams to a file in a way which does
> not change the visible contents of the file as seen by a normal open().
> It's not an issue of keeping the "main" contents of the file in a
> subfork; it's a question of adding subforks _without_ disturbing the
> main contents. That, by definition, changes the semantics of namei():
> you no longer get the whole contents of the file back when you do an
> open() and read().
>
> That is the crux of my objections. If we add such hidden information,
> then all our current tools (NFS, tar, cp, mv etc) fail. NFS in
> particular is a killer: by adding functionality to the fs which cannot
> be encoded in the standard NFS protocol, we lose the ability to share
> these files.

This seems to decide the issue right here: any solution based on ReiserFS,
or an expanded ext2fs, would be intrinsically unportable. Such techniques
could be used, but only as a Linux-local optimization. Otherwise, we kill
portability and transportability, which contradicts the entire point of
the game.

> If we want to add tagged information to a file, far better to do it via
> a dot directory. Keep the problem in user space where it belongs. Any
> extra efficiency that the fs has to offer will still be realised by such
> a mechanism.

Agreed -- though it might make sense to treat dot directories as just one
implementation of metadata, with others possibly available -- and some
standard library and flat-format to make this stuff portable.

--
Kenneth Albanowski (kjahds@kjahds.com, CIS: 70705,126)



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