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Re: [Linux-cluster] Re: [PATCH 00/14] GFS

On Aug 10, 2005, at 09:26:26, AJ Lewis wrote:
On Wed, Aug 10, 2005 at 12:11:10PM +0100, Christoph Hellwig wrote:

On Wed, Aug 10, 2005 at 01:09:17PM +0200, Lars Marowsky-Bree wrote:

So for every directory hierarchy on a shared filesystem, each user needs
to have the complete list of bindmounts needed, and automatically resync
that across all nodes when a new one is added or removed? And then have
that executed by root, because a regular user can't?

Do it in an initscripts and let users simply not do it, they shouldn't
even know what kind of filesystem they are on.

I'm just thinking of a 100-node cluster that has different mounts on different
nodes, and trying to update the bind mounts in a sane and efficient manner
without clobbering the various mount setups. Ouch.

How about something like the following:
cpslink() => Create a Context Dependent Symlink
readcpslink() => Return the Context Dependent path data
readlink() => Return the path of the Context Dependent Symlink as it
would be evaluated in the current context, basically as a
normal symlink.
lstat() => Return information on the Context Dependent Symlink in
the same format as a regular symlink.
unlink() => Delete the Context Dependent Symlink.

You would need an extra userspace tool that understands cpslink/ readcpslink to
create and get information on the links for now, but ls and ln could eventually
be updated, and until then the would provide sane behavior. Perhaps this
should be extended into a new API for some of the strange things several
filesystems want to do in the VFS:
extlink() => Create an extended filesystem link (with type specified)
readextlink() => Return the path (and type) for the link

The filesystem could define how each type of link acts with respect to other
syscalls. OpenAFS could use extlink() instead of their symlink magic for
adjusting the AFS volume hierarchy. The new in-kernel AFS client could use it
in similar fashion (It has no method to adjust hierarchy, because it's still
read-only). GFS could use it for their Context Dependent Symlinks. Since it
would pass the type in as well, it would be possible to use it for different
kinds of links on the same filesystem.

Kyle Moffett

Simple things should be simple and complex things should be possible
  -- Alan Kay

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