Re: [PATCH RFC 2/9] IB/core: Introduce Signature Verbs API

[Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 10/22/2013 7:41 PM, Hefty, Sean wrote:
>> I don't think so,
>> Signature MR simply describes a "signature associated" memory region
>> i.e. it is a memory region that
>> also defines some signature operation offload aside from normal RDMA
>> (for example validate & strip).
>> SGL are used to publish several rkeys for the server/target/peer to
>> perform RDMA on each.
>> In this case the user previously registered each MR which he wishes it's
>> peer to RDMA over.
>> Same story here, if user has several signature associated MRs, where he
>> wish his peer to RDMA over (in a protected manner),
>> he can use these rkeys to construct SGL.
>>
>>>     Why are the signature properties separate from the protection
>> information?
>>
>> Well,
>> Protection information is the actual protection block guards of the data
>> (i.e. CRCs, XORs, DIFs etc..), while the signature properties
>> structure is the descriptor telling the HCA how to
>> treat/validate/generate the protection information.
>>
>> Note that signature support requires the HCA to be able to support
>> INSERT operations.
>> This means that there is no protection information and the HCA is asked
>> to generate it and add it to the data stream
>> (which may be incoming or outgoing...),
> Would we lose anything making this a new operation for the QP, versus trying to hook it into the existing ib_post_send call?

If I understand correctly you are suggesting making it a verb? Well this 
operation is a fast-path operation - so I guess we will loose it in this 
case.
Take SCSI for example, for each IO operation submitted by SCSI 
mid-layer, transport layer should perform any protection policy that 
SCSI asked for.
 From this point of view, signature operation resembles fast 
registration (since the transport does not own the IOP data buffers, so 
it uses fast registration methods).
That is why we are hooking into ib_post_send.

Hope this helps.

Sagi.

--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html