Re: [PATCH RFC v2 02/10] IB/core: Introduce Signature Verbs API

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

On 3/11/2013 4:15, Sagi Grimberg wrote:
> On 11/1/2013 8:46 PM, Bart Van Assche wrote:
>> On 31/10/2013 5:24, Sagi Grimberg wrote:
>>> +/**
>>> + * Signature T10-DIF block-guard types
>>> + */
>>> +enum ib_t10_dif_bg_type {
>>> +    IB_T10DIF_CRC,
>>> +    IB_T10DIF_CSUM
>>> +};
>>
>> In SPC-4 paragraph 4.22.4 I found that the T10-PI guard is the CRC
>> computed from the generator polynomial x^16 + x^15 + x^11 + x^9 + x^8
>> + x^7 + x^5 + x^4 + x^2 + x + 1. Could you tell me where I can find
>> which guard computation method IB_T10DIF_CSUM corresponds to ?
>>
>> Bart.
>
> The IB_T10DIF_CSUM  computation method corresponds to IP checksum rules.
> this is aligned with SHOST_DIX_GUARD_IP guard type.

Since the declarations added in <rdma/ib_verbs.h> constitute an 
interface definition I think it would help if it would be made more 
clear what these two symbols stand for. How about mentioning the names 
of the standards these two guard computation methods come from ? An 
alternative is to add a comment like the one above scsi_host_guard_type 
in <scsi/scsi_host.h> which explains the two guard computation methods well:

/*
  * All DIX-capable initiators must support the T10-mandated CRC
  * checksum.  Controllers can optionally implement the IP checksum
  * scheme which has much lower impact on system performance.  Note
  * that the main rationale for the checksum is to match integrity
  * metadata with data.  Detecting bit errors are a job for ECC memory
  * and buses.
  */

Bart.

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