[dm-devel] Re: [PATCH] Handle multipath paths in a path group properly during pg_init

[Hannes Reinecke]

Chandra Seetharaman wrote:
> Resending the patch to get in patchwork...
> -------
> The problem reported by Moger Babu was caused due to the architectural
> change made when we moved from dm hardware handler to SCSI hardware
> handler.
> 
> Thanks Babu for finding and reporting the bug.
> 
> All of the hardware handlers, do have a state now, and they are set to
> active and (some form of) inactive. All of them have prep_fn, which use
> this "state" to fail the I/O without it ever being sent to the device.
> 
> As Babu has noted in his email, the pg_init/activate is sent on only one
> path and the "state" of that path is changed appropriately to "active"
> while other paths in the same path group are never changed as they never
> got an "activate".
> 
> Attached is a patch (compiled, tested, but not clean yet), which makes
> changes in the dm-multipath layer to send an "activate" on each paths in
> the path groups.
> 
> Mike (Anderson) and I had a discussion about whether to implement this
> in the dm-mulitpath layer or in the SCSI hardware handler layer and we
> came to a conclusion that it is best suited to be in the dm-mulitpath
> layer as it is the one that knows the relationship between different
> paths.
> 
> If it were to be done at the Hardware handler layer, then the hardware
> handler may end up having a different notion of the path relationship
> and hence may not work as expected by the dm-multipath layer.
> 
> This patch has been tested by Hannes in EMC storage. Babu and I tested it
> in LSI storage.
> ----------
> 
> Signed-off-by: Chandra Seetharaman <sekharan at us.ibm.com>
> 
Acked-by: Hannes Reinecke <hare at suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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