On 10/02/2014 02:05 PM, James Bottomley wrote: > On Thu, 2014-10-02 at 08:51 +0200, Hannes Reinecke wrote: >> On 10/01/2014 11:10 PM, Christoph Hellwig wrote: >>> On Wed, Oct 01, 2014 at 02:51:31PM -0400, Webb Scales wrote: >>>> Hannes, >>>> >>>> In megasas_change_queue_type(), is it possible for sdev->queue_depth to be >>>> greater than 256? >>>> >>>> Unless I'm misunderstanding the SCSI code, we can request a >>>> queue-depth/tag-map-size which is greater than 256, but, since the >>>> scsi_cmnd::tag field is an unsigned char, depths greater than 256 may >>>> overflow the field when high-numbered tags are used...do I have that right? >>> >>> Yes, we really need to increase the size of the tag field. SAM allows >>> a transport specific limit of up to 64 _bytes_ for it, although I don't >>> know implementation that large. Given that the block layer can generate >>> up to 32-bit tags both for the old blk-tag.c code and the new >>> blk-mq-tag.c version it would be good to use a u32 there. Can you send >>> me a patch? >>> >> Weeelll ... >> >> I'm afraid it's not _that_ easy. >> SCSI-II tagged queueing has some specific tag values: >> >> #define SIMPLE_QUEUE_TAG 0x20 >> #define HEAD_OF_QUEUE_TAG 0x21 >> #define ORDERED_QUEUE_TAG 0x22 >> >> drivers/scsi/vmw_pvscsi.c: >> e->tag = SIMPLE_QUEUE_TAG; >> if (sdev->tagged_supported && >> (cmd->tag == HEAD_OF_QUEUE_TAG || >> cmd->tag == ORDERED_QUEUE_TAG)) >> e->tag = cmd->tag; > > A SCSI-2 tag is a SPI two byte message. The first byte is the message > type. The values you have above identify the message type for simple, > ordered and head of queue tags. The *second* byte is the tag value. > > See page 55 and 56 of the SCSI-2 standard. There's no connection (or > shouldn't be) between the message type and the tag value, so it looks > like a bug in the pvscsi driver. > It is. I've already sent a patch. But that just proves the scmd->tag is essentially a duplicate and we should be removing it. 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
