Re: [PATCH 2.6.30] xprtrdma: The frmr iova_start values are truncated by the nfs rdma client.

Steve Wise
2009-04-27T19:32:04Z

Trond Myklebust wrote:
> On Mon, 2009-04-27 at 14:05 -0400, Trond Myklebust wrote:
>
>> It looks looks as though the bug is really that the IB code is using a
>> u64 to store dma handles. As an external user of the IB api, we really
>> shouldn't have to perform this sort of transformation. If it is
>> absolutely necessary, then it should be done by means of specialised
>> accessor functions to initialise/read iova_start value when given a
>> dma_addr_t.
>>
>> I'd therefore prefer the no-cast version (with eventual compiler
>> warnings), in the hope that eventually the IB folks will fix their
>> interface.
>>
>
> Translation: It looks to me as if the interface that we're using is a
> bit too corrupted with IB low level implementation grime. In the future,
> I'd like to see someone come up with a more high level interface for use
> by external code such as the sunrpc module.
>
>

Clarification: The iova_start isn't used to store dma handles. The
iova_start is the "address" base value that is advertised to a peer to
describe the base address of a memory region. The contents of that can
be more than just a dma handle...its up to the application. For
instance, you could advertise a iova_start of zero or a kernel VA as the
rdma server does. Also, the type is u64 because that is the size used
on the wire as part of the rdma (IB and iWARP) protocols.

Steve.