Block Integrity Rq Count Question

[Christoph Hellwig]

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.  

Can you reproduces this on Linux 4.14 / Linux 4.15-rc, please?   The
code in bio_integrity_prep should allocate the right number of
bio_vec entries based on what the device asks for, and for NVMe that's
always 1 in Linux as we don't support SGLs for the metadata transfer.

> 
> 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?
> 
> Jeff Lien
> Linux Device Driver Development
> Device Host Apps and Drivers
> jeff.lien at wdc.com
> o: 507-322-2416 (ext. 23-2416)
> m: 507-273-9124
> 
> 
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