iSCSI CRC check clarification

["De, Tandra" <Tandra_De@adaptec.com>]

Julian,

 

I followed few iSCSI CRC checking example threads and the thread file://www.pdl.cmu.edu/mailinglists/ips/mail/msg05931.html says that "Before transmission, the CRC bits must be reflected and complemented"; whereas, the iscsi- 08 draft only mentions about complementing the CRC before transmission. So attached you will find two software implementation code examples: crc_reflect.cpp and crc_no_reflect.cpp.

I ran few test cases with the attached example code and when I do reflect bits I get

                                0:        ff ff ff ff
                                4:        ff ff ff ff
                                8:        ff ff ff ff
                               12:        ff ff ff ff
                               16:        ff ff ff ff
                               20:        ff ff ff ff
                               24:        ff ff ff ff
                               28:        ff ff ff ff

 

                               32:        43 ab a8 62

in the transmission side, and the reception side I get 0x1c2d19ed.

 

But when I do not bit flip I get

                                0:        ff ff ff ff
                                4:        ff ff ff ff
                                8:        ff ff ff ff
                               12:        ff ff ff ff
                               16:        ff ff ff ff
                               20:        ff ff ff ff
                               24:        ff ff ff ff
                               28:        ff ff ff ff

 

                               32:        46 15 d5 c2

in the transmission side, and the reception side I do get 0x1c2d19ed though.

 

I like to clarify which implementation we should use so that both Initiator and Target will be in sync. validating the CRC. I appreciate if you could verify the attached files to see I am missing anytbing. Also I think that it would help everyone who are dealing with iSCSI CRC if you could put up the finalized version of the code in the reflector.

 

Thanks,

Tandra (tde@corp.adaptec.com)

crc_no_reflect.cpp

crc_reflect.cpp