Re: [PATCH RFC 2/3] svcrdma: Use device rdma_read_access_flags

[Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

On Tue, Nov 10, 2015 at 11:25:46AM -0700, Jason Gunthorpe wrote:
> I like this, my only comment is we should have a rdma_cap for this
> behavior, rdma_cap_needs_rdma_read_mr(pd) or something?

Yes, that's better than checking the protocol.

> > +		if (!(dev->device_cap_flags &
> > IB_DEVICE_MEM_MGT_EXTENSIONS)) {
> 
> Lets enforce this in the core, if rdma_cap_needs_rdma_read_mr is set
> the the device must also set IB_DEVICE_MEM_MGT_EXTENSIONS, check at
> device creation time.

The iWarp verbs spec requires them to be supported, so that should not
be an issue.

> > +	} else if (rdma_ib_or_roce(dev, newxprt->sc_cm_id->port_num)) {
> > +		/*
> > +		 * For IB or RoCE life is easy, no unsafe write access is
> > +		 * required and multiple SGEs are supported, so we don't need
> > +		 * to use MRs.
> > +		 */
> > +		newxprt->sc_reader = rdma_read_chunk_lcl;
> > +	} else {
> > +		/*
> > +		 * Neither iWarp nor IB-ish, we're out of luck.
> > +		 */
> >  		goto errout;
> 
> No need for the else, !rdma_cap_needs_rdma_read_mr means pd->local_dma_lkey is okay
> to use.

What would happen if someone tried to use NFS on usnic without this?
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