On Mon, 2011-12-19 at 13:36 -0500, Matthew Wilcox wrote: > On Mon, Dec 19, 2011 at 11:14:10AM -0600, James Bottomley wrote: > > On Mon, 2011-12-19 at 11:12 -0500, Matthew Wilcox wrote: > > > By the way, the same verbiage about tags being shared across LUNs is also > > > present in the SAS spec (and various other specs last time I looked, > > > which wasn't recently). > > > > I don't think so: The SAS spec still (as of 2.1) has the nexus being > > I_T_L_Q. That means a unique combination of initiator port, target > > port, lun and tag identify a nexus. To have the nexus be blind to the > > Lun (i.e. tags shared across LUNs) it would have to be identified by > > I_T_Q, which I haven't actually seen in any standard. > > sas2r14: > > 10.2.3 Device server error handling > If the SCSI target device performs tag checking and an SSP target port calls SCSI Command Received () with > a tag already in use by another SCSI command (i.e., an overlapped command) in any logical unit, the task > router and device server(s) shall abort all task management functions received on that I_T nexus and shall > respond to the overlapped command as defined in SAM-4. > > > I'm not even sure a transport would be allowed to override this; SAM is > > pretty clear (s 4.12 The Nexus Object) that a nexus is either I_T, I_T_L > > or I_T_L_Q. I_T_Q isn't listed as being allowable for a nexus. > > sam4r13f: > > 4.7.2 Command identifier > > A command identifier (i.e., the Q in an I_T_L_Q nexus) is assigned by a > SCSI initiator device to uniquely identify one command in the context of a > particular I_T_L nexus, allowing more than one command to be outstanding > for that I_T_L nexus at the same time. Each SCSI transport protocol > defines the size of the command identifier, up to a maximum of 64 bytes, > to be used by SCSI ports that support that SCSI transport protocol. > > SCSI transport protocols may define additional restrictions on command > identifier assignments (e.g., requiring command identifiers to be unique > per I_T nexus or per I_T_L nexus, or sharing command identifier values > with other uses such as task management functions). Hm, OK, that was actually something added to SAM-4. It's not present in SAM-3. However, it does look like SAS always tried to get away with this, notably by deciding in SAS-1 (which was SAM-3 based) that the Frame tag wasn't the same thing as a SAM-3 Q. James -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
