Re: Possible bug in scsi_lib.c:scsi_req_map_sg()

[Jens Axboe <jens.axboe@oracle.com>]

On Mon, Nov 27 2006, Mike Christie wrote:
> Mike Christie wrote:
> > Boaz Harrosh wrote:
> >> Playing with some tests which I admit are not 100% orthodox I have
> >> stumbled upon a bug that raises a serious question:
> >>
> >> In the call to scsi_execute_async() in the use_sg case, must the
> >> scatterlist* (pointed to by buffer) map a buffer that's contiguous in
> >> virtual memory or is it allowed to map disjoint segments of memory?
> > 
> > I thought they were continguous. I think James has said before that they
> > can be disjoint. When we converted sg it did not look like sg or st
> > supported disjoint. The main non dio path used a buffer from
> > get_free_pages so I thought that would always be contiguous. The dio
> > path then always set the first sg offset, but the rest it set to zero.
> 
> And the len is set to page size for the middle entries too.
> 
> But for the non DIO st path we can end up with some middle sg entires
> that are not a full page so that code in scsi_execute_async is broken
> for that.

If something doesn't work with non-contig sg entries, that would be a
bug. If the question is regarding holes in the sg list, that is probably
unchartered territory and I would not regard that as supported.

-- 
Jens Axboe