Re: dm-multipath based engenio-lsi hardware handler

[Chandra Seetharaman <sekharan@us.ibm.com>]

On Thu, 2007-03-22 at 13:04 -0500, Mike Christie wrote:
Mike,

Thanks for your comments.

> Chandra Seetharaman wrote:
> 
> Did you see may later revisions on this or Ed's updated handler? In the
> current kernel we do not need to allocate or manage our own bios. That
> was a old old hack from when the request did not have a end io. The hack
> is probably only needed for old distros. It is not needed upstream.
> 
> For dm based hw handlers you want to do something more like this:
> http://www.cs.wisc.edu/~michaelc/block/dm/v4/

Looks simpler. Can do it.

But, I am little confused though. I do not see the underlying functions
like dm_scsi_init/destroy_context_pool(), dm_scsi_execute_rq() etc., in
2.6.20/21-rc4 tree. Where is it available ?

Also, dm-emc.c (in 2.6.20/21-rc4) doesn't seem to use that model.

<snip>
> > 
> > static void rdac_pg_init(struct hw_handler *hwh, unsigned bypassed,
> > 			struct path *path)
> > {
> > 	struct rdac_handler *h = hwh->context;
> > 
> > 	switch (h->lun) {
> > 	case UNINITIALIZED_LUN:
> > 		submit_c8_inquiry(h, path);
> > 		break;
> > 	case UNSUPPORTED_LUN:
> > 		dm_pg_init_complete(path, MP_FAIL_PATH);
> > 		break;
> > 	default:
> > 		submit_c9_inquiry(h, path);
> > 	}
> > }
> > 
> 
> Why not just have userspace check and pass the LUN to the create
> function? This is not a review comment to do it. I am just asking if it
> is difficult to gather info in userspace and pass it down?

It should be possible to get the inquiry page from user space and
implement what you suggest. But, there is currently no storage device
specific interface (like path checkers) to do this. We have to either
add that interface or hack somewhere else(like path checkers) to do it.
Do you think it is worth it ?

Also, is it possible to get the lun info from user space without getting
the inquiry page ?

chandra
-- 

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    Chandra Seetharaman               | Be careful what you choose....
              - sekharan@us.ibm.com   |      .......you may get it.
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