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List:       lustre-devel
Subject:    [Lustre-devel] imports / obd's
From:       Peter Braam <braam () clusterfs ! com>
Date:       2003-08-23 14:54:24
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Hi Robert, Mike, 

During the last year we have shifted away from recovering a file
system to recovering an OSC/MDC device.

Multiple file system mounts on the same client should in principle be
able to share OSC's, and the imports where introduced to separate the
state associated with different users of the OSC/MDC device. Users
like file systems are NOT obd devices, so we needed a new abstraction.
So I envisaged having multiple imports associated with a single
OSC/MDC device.  Evidence of this history is that the obd_imports list
in struct obd_device is now unused (I just removed it on zconf).  I
think that was a good decision.

So this "import" concept has changed purpose a bit.  So it's fair to
say that at present an import contains the data associated with
OSC/MDC devices that describe recoverable elements associated with
network traffic (bulk and rpc).  Evidence of this is that the
client_obd has the import embedded in the obd structure. I think that
is fine - we are really recovering a device, and devices that can be
recovered like this have an import structure.

There appear to be two ways of using imports: one is the handle
mechanism, which seems too heavy handed for this purpose, and the
automatic destruction associated with refcounted handles is not
applicable.  Counting how many requests are using an import is good of
course.  The other is by storing a pointer in a device (like in the
obdfilter, to make calls to the mdc for log records).  That way is
probably more appropriate.  

Can we clarify this?

Thanks.

- Peter -


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