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Re: [Linux-cluster] new dlm control/configuration

On Thu, Mar 31, 2005 at 04:27:07PM +0800, David Teigland wrote:
> Sure, the mechanism used to export the locking API to user space is pretty
> inconsequential.  We're doing reads/writes on a misc device at the moment
> (used through libdlm of course.)  Going through an fs might be better but
> I'm not sure why.

A long time ago, we did consider a filesystem interface to the DLM. We rejected
it for a couple of reasons:

1) the mapping of locks to files is not a very clean one. Trying to squeeze
things like LVBs and ranges into the API soon gets very messy. Returning status
from asynchronous operations can make the coding rather complicated for
applications with multiple locks (you would need a file descriptor open for
each lock!). Also the hierarchy functions differently: a lock that has children
is still a lock, not just a directory.

2) At the time it was still very complicated to add new filesystems to the Linux
kernel. This has now changed of course.

I'll have a look at the OCFS2 filesystem and see if we can learn anything from
it though.



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