Block Integrity Rq Count Question

[Keith Busch]

On Fri, Dec 08, 2017 at 10:04:47PM +0000, Jeffrey Lien wrote:
> I've noticed an issue when trying to create an ext3/4 filesystem on
> nvme device with RHEL 7.3 and 7.4 and would like to understand how
> it's supposed to work or if there's a bug in the driver code.  
> 
> When doing the mkfs command on an nvme device using lbaf of 1 or 3 (ie
> using metadata), the call to blk_rq_count_integrity_sg in
> nvme_map_data returns 2 causing the nvme_map_data function to goto
> out_unmap and ultimately the request fails.  In the
> blk_rq_count_integrity_sg function, the check "if
> (!BIOVEC_PHYS_MERGEABLE(ivprv, iv))" is true causing a 2nd segment to
> be added.  This seems like it could happen regularly so my question is
> why the nvme driver map data function is only ever expecting 1
> segment?

The definition of the NVMe MPTR field says it has to be "a contiguous
physical buffer". It's not physically contiguous if you've two segments.