On 06/30/2010 01:30 PM, Boaz Harrosh wrote: > On 06/30/2010 12:23 AM, Brett Dennis wrote: >> Hello, >> >> Apologies for posting twice (messed up on the subject line of the first post...) >> >> In kernel 2.6.26, the implementation of __blk_rq_map_user changed and >> now includes a call to bio_copy_user: >> >> uaddr = (unsigned long) ubuf; >> alignment = queue_dma_alignment(q) | q->dma_pad_mask; >> if (!(uaddr & alignment) && !(len & alignment)) >> >> bio = bio_map_user(q, NULL, uaddr, len, reading); >> >> else >> >> bio = bio_copy_user(q, uaddr, len, reading); >> >> >> bio_copy_user uses the HBA's scatter-gather pages for the copy. The >> problem I face is that if the data is not aligned properly, or the len >> parameter does not divide properly, and the transfer is greater than >> the number of scatter-gather pages, the IO operation will fail. I am >> considering increasing the size of my data buffer to meet the >> length-alignment requirement and changing the 'len' parameter passed >> into blk_rq_map_user to include a larger size than my CDB transfer >> length. This way it will hit the bio_map_user branch instead of the >> bio_copy_user branch and I won't have to worry about insufficient >> sg-pages. The tape device should still honor the CDB write length, so >> unless there are other limitations imposed by the Linux kernel or SCSI >> subsystem, I think this is a workable solution. Does anyone in this >> list know if there are requirements against sending a larger buffer >> length than CDB transfer length? >> > > It depends. If you are issuing BLOCK_PC commands then you are in the clear. > If an FS_PC commands then your ULD must take proper care at completion. > What ULD are you using? > Sorry I missed the scsi_execute_async() part in the title. So yes it is BLOCK_PC. I think it should be fine, unless some LLD would break because LLDs and HW do funny things. I'd try it out. If you have problems with particular HW, perhaps keep a black-list flag. You might expect some residual returns from some LLDs. >> Thanks in advance. >> >> Brett Dennis >> IBM tape device driver developer > > Boaz -- 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
