[PATCH] nvmet-passthru: Cleanup nvmet_passthru_map_sg()

[Christoph Hellwig]

On Thu, Oct 15, 2020 at 10:01:30AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2020-10-15 1:56 a.m., Christoph Hellwig wrote:
> > On Fri, Oct 09, 2020 at 05:18:16PM -0600, Logan Gunthorpe wrote:
> >>  static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
> >>  {
> >> -	int sg_cnt = req->sg_cnt;
> >>  	struct scatterlist *sg;
> >>  	int op_flags = 0;
> >>  	struct bio *bio;
> >>  	int i, ret;
> >>  
> >> +	if (req->sg_cnt > BIO_MAX_PAGES)
> >> +		return -EINVAL;
> > 
> > Don't you need to handle larger requests as well?  Or at least
> > limit MDTS?
> 
> No and Yes: there is already code in nvmet_passthru_override_id_ctrl()
> to limit MDTS based on max_segments and max_hw_sectors.

But those are entirely unrelated to the bio size.  BIO_MAX_PAGES is
256, so with 4k pages and assuming none can't be merged that is 1MB,
while max_segments/max_hw_sectors could be something much larger.