Re: SCSI Generic version 4 interface, release 1.2

[Mike Christie <michaelc@cs.wisc.edu>]

Pete Wyckoff wrote:
> dougg@torque.net wrote on Wed, 14 Mar 2007 12:18 -0400:
>> After reviewing this post by Pete Wyckoff:
>> http://marc.theaimsgroup.com/?l=linux-scsi&m=117278879816029&w=2
>>
>> I decided to update my sg v4 interface document originally
>> posted 20061106 which I will now call release 1.1 :
>> http://lwn.net/Articles/208082/
>>
>> Pete was proposing to put back din_iovec_count and
>> dout_iovec_count that had been dropped out of bsg but
>> had been in release 1.1 . Hmm.
>>
>> Some other items have been picked up from the bsg
>> implementation plus the suggestion from LSF'07 to
>> add dout_resid.
>>
>> See the attachment, comments welcome.
> 
> Do you want to define the iovec format too?  As I commented in my
> patch, v3 sg_iovec has pointers with 32/64-bit issues.  Would be
> nice to see you declare v4 sg_iovec as pure u64.  (By the way, don't
> use the patch:  casting from the new to the old can put junk in the
> top half of the 64-bit sg_iovec.iov_len).
> 
> Another issue I wonder about is queue DMA alignment.  In bsg,
> blk_rq_map_user will use a bounce buffer if the user-supplied start
> and end addresses are not aligned.  sg will happily map user pages
> at any offset without checking, although I haven't checked if Mike's
> patches change this.  ll_rw_blk.c says regarding blk_rq_map_user:
> 

Currently and before any of my patches, sg checked the start
        if (((unsigned long)hp->dxferp &
                        queue_dma_alignment(sdev->request_queue)) != 0)
It did not check the start and end like blk_rq_map_user.

With my updated patches, blk_rq_map_user is just checking the start.
There was a thread about not checking the end on linux-scsi. I will try
to dig it up. A couple kernels ago the bio map helpers were modified to
only check the start.