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List:       kde-look
Subject:    Re: Moving away from app-centric mimetypes (e.g. kword)
From:       Brad Hards <bhards () bigpond ! net ! au>
Date:       2002-05-15 21:17:40
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On Thu, 16 May 2002 04:42, Allan Sandfeld Jensen wrote:
> On Wednesday 15 May 2002 13:37, Brad Hards wrote:
> > > This is why, ultimately, no metadata system without kernel support can
> > > ever be complete.
> >
> > This is a big ask too. Remember that KDE runs on more than just Linux.
> > Consider Solaris and Tru64, plus the BSDs.
>
> I would you wish you would stop talking about kernels, what you really mean
> is without filesystem support. It is important to remember kernels are not
> the only ones to supply filesystems.  e.g. KIO is filesystem!
> So is MIME for emails or the tar-format for tar-balls.
I think that there is some confusion, because this presupposes an 
implementation.
Leave aside higher level access mechanisms for now, and consider the common 
core that works for
KDE, gnome, command line, rsync, etc.
At this level, we have whatever the kernel (and posix I/O, maybe) gives us.
If you embed the metadata in the same file (which is my proposal, broken on 
"plain jpeg" files),
you get all this support. If you embed the metadata in a seperate file, 
associated with the file
the metadata applies to, then you need to be careful about keeping the file 
and its metadata together. 
[root@localhost bradh]# umount /dev/hda3
[root@localhost bradh]# mount -t vfat /dev/hda3 /mnt/dos
[root@localhost bradh]# ls -l /mnt/dos/Brads/A*
-r-xr-xr-x    1 root     root       697344 Nov 21  2000 
/mnt/dos/Brads/Annotated Issues Log.doc
[root@localhost bradh]# umount /dev/hda3
[root@localhost bradh]# ls -l /mnt/dos/Brads/a*
-r-xr-xr-x    1 root     root       697344 Nov 21  2000 
/mnt/dos/Brads/annota~1.doc
[root@localhost bradh]# umount /dev/hda3
[root@localhost bradh]# mount -t msdos /dev/hda3 /mnt/dos
[root@localhost bradh]# ls -l /mnt/dos/Brads/a*
-r-xr-xr-x    1 root     root       697344 Nov 21  2000 
/mnt/dos/Brads/annota~1.doc
[root@localhost bradh]# umount /dev/hda3

Now if I'd copied the /mnt/dos/Brads directory in one case, I'd have the full 
name (and VFAT attributes), but in the other case, it'd be lost.

So it you implement a virtual filesystem over the top of the standard 
directory, then you have to make sure that only access to the standard 
directory is over the virtual filesystem. That restricts you to using a 
subset of the normal tools.

However if you implement the virtual filesystem over a file (like a zip or 
tarball), then you can get away with using standard file utilities.

> If you have ever been learned anything about protocol-stacks you should
> know what I am talking about. This is application or representation-layer
> stuff, it does not need, and therefore _should_ not interfere with lower
> levels and certainly not the 10+ different kernels KDE is available on.
The first part of this comes across as condescending.

You might be able to do a userspace filesystem, and mount it using the 
loopback interface, but it would still need some kernel support.

In any case, we can implement it without a full virtual filesystem, and get 
most of the functionality required. In any case, it would allow the userspace 
presentation (which should be mostly indpendent of the underlying 
implementation) to be determined. That is a more useful thing to be 
discussing in any case (especially on a look'n'feel list)

Brad

-- 
http://conf.linux.org.au. 22-25Jan2003. Perth, Australia. Birds in Black.

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