Re: [PATCH 05/15] nvme-rdma: Add metadata/T10-PI support

[Christoph Hellwig <hch@lst.de>]

On Tue, Nov 05, 2019 at 06:20:16PM +0200, Max Gurtovoy wrote:
> For capable HCAs (e.g. ConnectX-4/ConnectX-5) this will allow end-to-end
> protection information passthrough and validation for NVMe over RDMA
> transport. Metadata offload support was implemented over the new RDMA
> signature verbs API and it is enabled per controller by using nvme-cli.
> 
> usage example:
> nvme connect --pi_enable --transport=rdma --traddr=10.0.1.1 --nqn=test-nvme
> 
> Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
> Signed-off-by: Israel Rukshin <israelr@mellanox.com>
> ---
>  drivers/nvme/host/rdma.c | 346 ++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 298 insertions(+), 48 deletions(-)
> 
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 05f2dfa..16263b8 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -48,6 +48,12 @@ struct nvme_rdma_qe {
>  	u64			dma;
>  };
>  
> +struct nvme_rdma_sgl {
> +	int			nents;
> +	struct sg_table		sg_table;
> +	struct scatterlist	first_sgl[SG_CHUNK_SIZE];

I think this needs some rework.  Kill the first_sgl pointer, and then
just set the pointer in the table to address found by pointer
arithmetics behind the nvme_request in the allocation.

We also have an open todo item to not actually allocate SG_CHUNK_SIZE
entries, but a much smaller value like in SCSI.

Also the whole switch to use struct sg_table should be a separate prep
patch.

> -	struct sg_table		sg_table;
> -	struct scatterlist	first_sgl[];
> +	/* T10-PI support */
> +	bool			is_protected;

This is a bit of an odd variable name.  Why not use_pi or something like
that?

Also all the new code should only be built if CONFIG_BLK_DEV_INTEGRITY
is set.

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