Re: [Summary] Meta-data/filesystem-encapsulation

[Christopher Curtis <ccurtis ee fit edu>]

On Fri, 14 Aug 1998, Miles Egan wrote:

> On Sat, 15 Aug 1998, Kevin Littlejohn wrote:
> 
> > I think it comes down to there is no way to keep metadata and not loose it
> 
> This sounds like a real mess to me and I think we should think very
> carefully before we try and implement a scheme like this.  It seems to me
> that you'll have to change the filesystem to make something like this
> really robust enough to be a benefit to the user.  Changing the filesystem
> just isn't an option for Linux.

Of course it is.  =)

The problem, though, comes in because you lose portability.  Whatever
system is chosen should support two methods: the preferred being a
filesystem modification type, the "safe" being some lesser alternative, be
it a combination mime.types for "classes" and flatfile/dbm for individual
attributes or what have you. 

Regarding changing the filesystem, this should not be a problem.  ext2
already supports many "attributes" (man chattr), one of which is
"compressed".  Even though this isn't yet supported, the idea can be used.
Add an attribute "metadata" or "extended attribute" (oops, is that too
much OS/2?) and this flag will get set in the file's inode.  Then when
that file is read or written to, a header can be written (or a whole
block, but that could be too wasteful for small files) as well.  This
would take some hacking of the standard C library I suspect, unless a
LD_PRELOAD library is used.  As far as this slowing down running files, I
bet it's a virtually insignificant performance hit, especially once the
library has already been preloaded once.

Probably best is a GNOME wrapper class around fread() and fwrite() where
the header can be automatically prepended for supported files and/or the
dbm/flatfile be updated simultaneously.  And while the dbm/flatfile could
get out of sync, it should be pretty easy to get something like that
cleaned up fairly painless and easily from cron or something.

The nice thing about HPFS as well (and I guess NTFS, too) is that the EAs
could grow or shrink so that things like thumbnails of images could be
stored with the file itself as an attribute.  Of course this got lost
being copied to floppy, etc, but GNOME will have all those same problems.

$0.02
--
Christopher Curtis               - http://www.ee.fit.edu/users/ccurtis
                                 - System Administrator, Programmer
Melbourne, Florida  USA          - http://www.lp.org/