> -----Original Message----- > From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi- > owner@xxxxxxxxxxxxxxx] On Behalf Of Steffen Maier > Sent: Thursday, August 09, 2012 9:15 AM > To: linux-scsi@xxxxxxxxxxxxxxx > Cc: Parikh, Neerav; Brattain, Ross B; Love, Robert W; James Bottomley; > Martin Peschke; Daniel Hansel > Subject: FC_PORTSPEED semantics confusion and zfcp regression > > Earlier, commit > 1832a5862f2e1b4e5835611ee14bc30a8ed3cad5 > "[SCSI] change port speed definitions for scsi_transport_fc" > changed the semantics of FC_PORTSPEED defines to match the Report Port > Speed Capabilities (RPSC) ELS of FC-GS/FS-LS instead of FC-HBA/SM-HBA. > It also mentions the problem that FC-HBA/SM-HBA and FC-GS/FC-LS contain > somewhat contradicting bit definitions for port speed. > > Lately, commit > a9277e7783651d4e0a849f7988340b1c1cf748a4 > "[SCSI] scsi_transport_fc: Getting FC Port Speed in sync with FC-GS" > reverted this. > (See also http://marc.info/?l=linux-scsi&m=132892310322550&w=2.) > > However, there does not seem to be an explicit explanation of this. > While the source code comment of struct fc_host_attrs says its fields > adhere to HBAAPI 2.0, the comment of the FC_PORTSPEED defines does not > explicitly do so and a (new) user of the latter might not see the > relation to the structure fields, esp. since there is no obvious > relation in terms of C types other than being type compatible to a > generic int. > The commit message also does not say so but mentions SM-HBA along with > FC-GS without stating that they contradict themselves and FS-GS even > within the same document since it defines both RPSC ELS and FDMI port > attributes. > > 1) Is this change of semantics deliberate? > > The commit message of a9277e7 states that user space is not affected > since it only sees text strings in the corresponding sysfs attributes. > > Actually, commit c3d2350a8420dbf9d48f5f8a0fb72117bfcbc1b0 > "[SCSI] fc_transport: update potential link speeds" > deliberately decided against syncing the bit definitions because of a > potential binary-incompatibility. > > Is there some use of the bit definition that is not as transparent as > the text string based sysfs interface of an fc_host? E.g. using > scsi_transport_fc.h in user space libraries or applications (if this is > even allowed to be exported to user space)? I could find an in-kernel > binary use in libfc/fc_lport.c which could alternatively do a > conversion > between the old RPSC ELS format of fc_host_{supported_}speed{s}() (and > libfc/fc_lport.c which has probably the same format as fc_host) when > building the FDMI blob in scsi/fc_encode.h:fc_ct_ms_fill()? While adding FC-GS FDMI support for the open FCoE stack (that uses libfc) to register the port speed attributes(via FDMI) correctly either I would need local libfc definitions that would translate the in kernel FC_PORTSPEED to specification values or get these defines in sync with the FC-GS/SM-HBA/HBAAPI spec level to not do these translations that other drivers seem to be doing. I chose to do the former in this commit. One thing that I seem to miss is the RPSC ELS have some different definitions for speed as compared to the FC_PORTSPEED before this commit as well. Does the zfcp HBA FW do some internal conversion resulting into speed values that were in sync with the prior FC_PORTSPEED values? > > 2) Why did commit a9277e7 change the kernel internal bit definitions? > > The zfcp LLDD has been copying the supported speeds value directly from > what is reported by the HBA since the latter adheres to the RPSC ELS > format for line speeds. Since commit a9277e7 this is broken now and we > see 10 Gbit instead of 4 Gbit in the supported_speeds sysfs attribute > of > the fc_host. I don't mind converting zfcp to an explicit finite bit > conversion based on individually defined constants, esp. since all > other > FC LLDDs (qla2xxx, bfa, lpfc, ibmvscsi, fnic, mptfc) seem to do so > already. The only slight drawback I can see is that the code needs to > be > touched for new HBA generations supporting new port speeds. This is the same problem I was trying to avoid while you were trying to reuse the values reported by HBA to the OS; whereas I was copying the speed values set for the libfc fc_lport instance to FDMI speed related attributes as is. Copying them as is was reporting incorrect speeds on the FC switch side FDMI database. > > 3) Should we have port speed defines for both RPSC ELS (in > include/fc/fc_els.h?) and FDMI port attributes (in > include/scsi/scsi_transport_fc.h? unless the bit semantic change gets > reverted)? > > This way I could reuse the former to convert to the latter within zfcp > and other users can reuse it with regard to RPSC ELS. I would send a > patch if we agree on this. I'm okay with either of the approach and if you choose the former (revert) then I'll make necessary changes in libfc part to convert values internally there. Also, regardless of the approach you decide on wouldn't zfcp need to make sure the speed values reported by HBA FW is in sync with the in kernel values? > > 4) Either way, should the port speed defines indicate RPSC ELS vs. FDMI > more explicitly in their identifier names, in order to avoid future > confusion? If you chose to revert the a9277e7 then perhaps you don't need multiple speed definitions. > > Regards, > Steffen > > Linux on System z Development > > IBM Deutschland Research & Development GmbH > Vorsitzende des Aufsichtsrats: Martina Koederitz > Geschäftsführung: Dirk Wittkopp > Sitz der Gesellschaft: Böblingen > Registergericht: Amtsgericht Stuttgart, HRB 243294 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" > in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
