On 04/08/2013 05:37 PM, Tomas Henzl wrote: > On 04/05/2013 05:24 PM, James Smart wrote: >> >> On 4/4/2013 6:17 AM, Hannes Reinecke wrote: >>> On 03/31/2013 07:44 PM, Tomas Henzl wrote: >>>> What we can do is to decode the LUN and compare it to max_lun provided by the driver, >>>> I think that sg_luns is able to do that, so what is needed is just to follow the SAM. >>>> >>>> I have seen reports of problem on three different drivers connected to various >>>> external storage, all of them having the same basic reason - the driver sets a max_lun >>>> and then LUN comes encoded with a newer addressing method and something like this is shown >>>> 'kernel: scsi: host 2 channel 0 id 2 lun16643 has a LUN larger than allowed by the host adapter' >>>> >>>> Decoding the real LUN value would fix this problem, by decoding is only meant the use in >>>> scsi_report_lun_scan. The LUN would be stored exactly the same way as it is now. >>>> I know we can patch the certain drivers too, but when max_lun were what the name says >>>> - max LU number, it would fix my problem very easy. >>>> >>> Errm. >>> >>> No. Decoding LUNs is _evil_. It has only a relevance on the target, >>> and even then it might choose to ignore it. >>> So we cannot try to out-guess the target here. > OK, I can see the problems with decoding the LUN one of them is the need to > again encode the LUN to address format + number. I'm not sure if the hw > would work if another address mode were used. > > When we understand the LUN as a complex structure then it makes no sense > to compare to max_lun as a number - http://lxr.linux.no/#linux+v3.8.6/drivers/scsi/scsi_scan.c#L1471 > Oh, but it does. See below. >>> The error you're reporting is that lpfc is setting max_luns to >>> '255', which of course is less than 16643. Increasing max_luns on >>> lpfc to '0xFFFF' will fix your problem; nothing to do with 64-bit >>> LUNs ... > I think I haven't mentioned lpfc, but it doesn't matter. > Fixing this in individual drivers by increasing the max_lun is not easy, > because the firmware could have some reasons for the max lun (some tables, ..., > fact is I have no idea how this is implemented in the hw). > If the fix for this were just to set max_lun to 0xFFFF in every driver > it means that we could remove the max_lun and the test completely. > > A kernel option like 'ignore_max_lun' would help, but I somehow dislike it, > what do you think? > Well, I've thought about this, too. You are right in the sense that 'max_lun' actually has a double meaning. First it's being used as the upper limit for sequential scan, where is has a strictly sequential meaning. So any internal LUN structure doesn't come into play here are we're just 'counting'. Secondly it's being used as a simple validation for any LUN numbers reported via REPORT LUNS. Here it the max_lun value actually refers to the amount of _bits_ in a LUN number the HBA can transfer. Again, the internal LUN structure doesn't come into play here; this is purely a hardware limitation on the HBA. Whether a LUN is valid or not is none of our concern; if the target accepts the LUN is has to be valid. If it doesn't then we don't care whether the LUN structure is valid or not; there is no device to be had anyway. However, after consulting SAM it is true that a plain 'max_lun' is incorrect for any LUN value higher than 255. LUN values higher than 255 should be represented with the 'flat space addressing' model, ie bit 6 should be set. Sadly, the various SAM revisions differ on how LUNs lower than 255 should be treated; they might or might not have set the flat space addressing model. So yeah, I guess we should be handling the HBA restriction different from the max_lun setting. I see to cook up a patch. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- 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
