Re: ioctls for gnome-vfs

[Alex Graveley <alex ximian com>]

On Mon, 2002-11-18 at 03:55, Alexander Larsson wrote:
> On 15 Nov 2002, Alex Graveley wrote:
> 
> > Hi,
> > 
> > On Fri, 2002-11-15 at 15:09, Joe Shaw wrote:
> > > I'm not so sure.  Maybe it's just the terminology, but "metadata" to me
> > > means any arbitrary information layered on top of files, probably
> > > persistent.  Image thumbnailing seems like a good use of metadata to
> > > me.  
> > > 
> > > This seems more like additional parameters on the method itself...
> > > things like setting HTTP headers for a specific request or passive mode
> > > on FTP.
> > 
> > I think it depends completely on the metadata being twiddled.  For
> > instance: idealy we would want metadata stored on an mp3 and prefixed
> > with "id3-tag:" to be stored in the id3 section of the file itself. 
> > Just as likely is setting headers in an http transfer, before a read or
> > write; in this case the meta-data should only be available for setting
> > on an open file handle, and not on a URI.
> 
> Meta-data changes changing the actual file? Ick! That wouldn't be metadata 
> at all, that would be data.

I don't agree at all.  You should be able to view and change the author
of a Word document without having to know the format.  You should be
able to look at the playing time of a .ogg without knowing how.  You
should be able to tell the operating system to compress or encrypt a
file without it effecting gnome_vfs_read()/write().  

> > Also an issue for me is the that i can't think of any good reason for a
> > file-control api.  We don't expose sockets or file descriptors.  Ans the
> > example that alexl posted is certainly metadata and not an ioctl, since
> > the attribute is associated with a file and would presumably remain for
> > its lifetime.
> 
> I'd love to have a real metadata API in gnome-vfs, but I don't think it 
> can replace a real per-backend ioctl style operation. While for some 
> designs of metadata you might be able to hack it into doing backend 
> specific things that is really not what metadata is for.

I don't agree :)  Can you give me some useful examples of ioctls in
gnome-vfs?  

Also, I really don't like the thought of a per-backend -anything-. 
Backends are singletons, and allowing changes to them from one component
that might easily break the behavior that another component is relying
on is bad. 

And I don't think it would be a hack to do ioctls through metadata.  I
think it makes sense, and will reduce APIs that will essentially overrun
each other in logical purpose.

> Metadata is auxilliary information about the file, some metadata is 
> already stored by the os, such as file modification dates, permissions 
> etc. Others (as used by nautilus) are custom icon, icon position, icon 
> stretch factor, etc.

Yup, and it will rely on good namespacing to know which is which, and
whether what you are setting will effect the operating system, nautilus,
or the file's content itself.

-Alex

-- 
 on the canvass of life, incompetence is my paintbrush.