Re: [GNOME VFS] Re: Daemons [Was: gob inside gnome-vfs ...]

[Maciej Stachowiak <mjs noisehavoc org>]

On 27Jun2002 12:14PM (-0700), Seth Nickell wrote:
> On Thu, 2002-06-27 at 02:12, Michael Meeks wrote:
> > On Thu, 2002-06-27 at 07:19, Maciej Stachowiak wrote:
> > > That seems like it might be bad for stability - one user-context
> > > daemon crashing could potentially lead to a lot of data loss if it
> > > took down all the others.
> > > 
> > > But it would definitely make sense to have a single gnome-vfs daemon
> > > that combined credentials caching, metadata, and whatever other shared
> > > services would be provided via gnome-vfs.
> 
> I think Metadata is less important, we have the same synchronization
> issues with Metadata that we would with any standard file; that is to
> say that I'm not sure we need a daemon for metadata and not one for the
> whole filesystem. 

The kernel is the daemon for the whole filesystem. It ensures that the
view of the filesystem is always as if some series of outstanding
write operations had completed in the correct order.

Metadata generally involves a read-modify-write cycle, and therefore
the kernel's guarantees are not enough, and metadata can get lost.

In fact, we initially thought we could punt on this for Nautilus, even
though both the main nautilus executable and some out-of-process
components could change metadata. But we discovered that in practice
this would result in metadata being lost, so we changed to a model
where nautilus acts as the metadata server for the components.

It is this concrete experience that convinces me that metadata
(without direct kernel-level support) requires a server.

 - Maciej