Hi Sagi, > RFC-7143 states: > "the Expected Data Transfer Length field contains the number of bytes of > data involved in this SCSI operation." > Since this field relates to *data bytes* I kept T10-PI implicit wrt this > field. The iSCSI target calculates the > total transfer length (data + protection) from the cdb transfer length > field and protect bits.
That is wrong. At the SCSI transport interface (both iSCSI and FCP are SCSI transports), the concept of "data bytes" includes SCSI protection information. > In FC, the fc_dl field was updated to relate to the total number of > transfer bytes and includes > data and protection bytes. virtio_scsi was added with a header PI > section (virtio_scsi_cmd_req_pi). That is the correct approach. At the SCSI transport interface (both FCP and iSCSI are SCSI transports), no distinction is made between user data and protection information. therefore, a transfer of 512 bytes of user data + 8 bytes of protection information is a 520 byte transfer for both protocols. The authority for this is SAM-5, or SAM-4 if one wants to refer to an approved standard. Neither are open to interpretation on this point. All SCSI transports are supposed to behave the same way. I hope this can be corrected quickly. Thanks, --David > -----Original Message----- > From: Sagi Grimberg [mailto:[email protected]] > Sent: Sunday, May 25, 2014 11:31 AM > To: [email protected]; Mike Christie; Nicholas A. Bellinger > Cc: linux-scsi; target-devel; Oren Duer; [email protected]; Or Gerlitz; > [email protected]; [email protected]; [email protected]; Black, David > Subject: iSCSI Expected Data Transfer Length for T10-PI > > Hey All, > > Recently, iSER end-to-end T10-PI support maid it mainline. > I am wandering about the impact T10-PI should or shouldn't have on iSCSI > header > field "Expected Data Transfer Length". > > RFC-7143 states: > "the Expected Data Transfer Length field contains the number of bytes of > data involved in this SCSI operation." > Since this field relates to *data bytes* I kept T10-PI implicit wrt this > field. The iSCSI target calculates the > total transfer length (data + protection) from the cdb transfer length > field and protect bits. > > In FC, the fc_dl field was updated to relate to the total number of > transfer bytes and includes > data and protection bytes. virtio_scsi was added with a header PI > section (virtio_scsi_cmd_req_pi). > > So my question is, should this field be updated to explicitly include > T10-PI bytes like the FC equivalent fc_dl? > Or should T10-PI bytes be implicit? > > I want to pin down this one to avoid a situation where the standard is > open for interpretations. > > Thanks, > Sagi. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
