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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] ExpDataSN overloadDear list members, I've just noticed that ExpDataSN is used to denote a lot of different things (all references w.r.t. to draft 11): 1) the total number of Data-In PDUs that a target has sent to complete a SCSI (read-like) command (2.5.1.2, 9.4.7, 6.6, E.9.2); 2) next concecutive input DataSN number expected by the initiator for the referenced command in previous execution, used in TASK REASSIGN (6.1.2, 9.5.4); 3) internal target variable used to track the next DataSN Expected from the initator or something like that (6.2). Regarding use 1: this is the most widespread, and there is nothing to object, except perhaps that the name ExpDataSN doesn't convey the exact meaning--- "TotalDataPDUs" or "NumDataPDUs" or something like that. Anyway, I can live with this. Regarding use 2: the name conveys the meaning, but I don't like the wording of this spot in 6.1.2: "... for example taking advantage of ExpDataSN in the iSCSI command PDU for read commands...". The problem is that "read commands" don't have ExpDataSN in the PDU, it's the "Task Management Function Request" PDUs that do. Task Management Function Request PDUs are, of course, "iSCSI command PDUs", but the whole thing makes it too easy to make the mistake of remembering (the ill-named) ExpDataSN field in SCSI Response PDU, at which point nothing makes sense anymore, because that's the other meaning of ExpDataSN. I would appreciate if somebody could rephrase the sentence. I'll even volunteer: "In reassigning connection allegiance for a command, the targets SHOULD continue the command from its current state. For example, when reassigning read commands, the targets SHOULD take advantage of the ExpDataSN field provided by the Task Management Function Request PDU (which must be set to zero if there was no data transfer) and bring the command to completion by sending (or resending) the status." Regarding use 3: I don't understand this. The last two sentences of 6.2 seem to be talking about Data-Out PDUs, therefore uses 1 and 2 of ExpDataSN (that are both Data-In PDU related) don't apply here. I'm concluding that these sentences are making some (unwelcome) assumptions about target implementation details (e.g., ExpDataSN in the role of a variable used to track the DataSN of the next Data-Out PDU that a target expects to receive for this command). If so, I would like such assumptions dropped and no MUSTs (and MAYs) imposed on a target implementation. If I'm wrong, somebody please explain to me what was meant here. "Bonus" :-) problem: While we're at 6.1.2, the start of the 3rd paragraph also got me thinking and browsing the draft for quite a while. I don't like the "This is true even when the CmdSN can be reliably ascertained..." phrase. The problem is, I don't see how it could not be reliably determined for rejected PDUs. My thinking is that the only way to not be able to reliably determine CmdSN is in the case of header digest errors. But in this case, the PDU must be silently dropped, and not be answered with a Reject PDU. Am I wrong somewhere? If not, can we change the sentence I mentioned to something that explains that for rejected PDUs, the target will necessarily have a good CmdSN, but still must not use it"? Help on these issues will be much appreciated. Martins Krikis, Intel Corp. Disclaimer: These opinions are mine only and may not reflect those of my employer. __________________________________________________ Do You Yahoo!? Try FREE Yahoo! Mail - the world's greatest free email! http://mail.yahoo.com/
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