On Sat, Sep 03, 2005 at 10:41:40PM -0700, Andrew Morton wrote:
> Joel Becker <[email protected]> wrote:
> >
> > > What happens when we want to add some new primitive which has no
> > > posix-file analog?
> >
> > The point of dlmfs is not to express every primitive that the
> > DLM has. dlmfs cannot express the CR, CW, and PW levels of the VMS
> > locking scheme. Nor should it. The point isn't to use a filesystem
> > interface for programs that need all the flexibility and power of the
> > VMS DLM. The point is a simple system that programs needing the basic
> > operations can use. Even shell scripts.
>
> Are you saying that the posix-file lookalike interface provides access to
> part of the functionality, but there are other APIs which are used to
> access the rest of the functionality? If so, what is that interface, and
> why cannot that interface offer access to 100% of the functionality, thus
> making the posix-file tricks unnecessary?
We're using our dlm quite a bit in user space and require the full dlm
API. It's difficult to export the full API through a pseudo fs like
dlmfs, so we've not found it a very practical approach. That said, it's a
nice idea and I'd be happy if someone could map a more complete dlm API
onto it.
We export our full dlm API through read/write/poll on a misc device. All
user space apps use the dlm through a library as you'd expect. The
library communicates with the dlm_device kernel module through
read/write/poll and the dlm_device module talks with the actual dlm:
linux/drivers/dlm/device.c If there's a better way to do this, via a
pseudo fs or not, we'd be pleased to try it.
Dave
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