high-performance, distributed filesystem intended for use in large
clusters. It is the latest effort from Peter Braam, who has, in the past,
been responsible for the Coda and InterMezzo filesystems. Lustre has not
been proposed for merging yet, but it is already in production use at a
number of large supercomputing centers. Companies like Dell, Cray, and HP
have been helping with its development.
Mr. Braam has recently posted the second
iteration of a patch intended to pave the way for inclusion of Lustre.
This patch exports some symbols needed by Lustre and makes various virtual
filesystem changes. With this patch in place, sites using Lustre would be
able to load the filesystem as a separate module without having to patch
the kernel directly. Since many of these sites, it seems, use "enterprise"
distributions and cannot patch their kernels without invalidating their
support agreements, this matters. Almost everybody involved would like
Lustre to be usable on mainline kernels.
Most of the technical objections to the Lustre patches have been
addressed; to that end, many changes were made since the first posting.
There remains one objection which can still be heard from a small number of
developers, however: the patch should not be merged because it provides
interfaces which are not used by any code in the kernel tree. This
argument has been heard before; the Linux security module patches, for
example, were opposed on this basis.
It is not hard to understand a general reluctance to include (seemingly)
unused APIs in the kernel. If an interface is not in active use, chances
are that, when somebody does try to use it, they will find that it
does not work as advertised. Unused code tends to rot over time. And all
code bloats the kernel, so it makes sense to hold off on adding new code
until there is a clear use for it.
It is also true, however, that the addition of new interfaces can help
drive development in useful directions. The hooks needed by Lustre should
be useful for a number of distributed filesystems, starting with NFS and
going on to the various other cluster-oriented filesystems. Until the new
interface is available, however, no filesystem will start using it. And,
in any case, there is a clear user here in the form of Lustre, which is an
available, GPL-licensed filesystem.
Your editor, putting on his highly unreliable clairvoyant cap, figures that the
Lustre developers will eventually get their wish. Certain developers will
likely make them sweat for it, however, forcing a few more iterations on
the patch before it can be accepted. But in the end, nobody disagrees with
the goal (being to provide a high-quality distributed filesystem for
high-performance clusters) and the patches were written with a relatively light hand.
There is no real reason to keep them out of the kernel.
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