[PATCH] nvme: scan sequentially only when list scan unsupported

[Uday Shankar]

> Currently, if nvme_scan_ns_list fails, nvme_scan_work will fall back to
> a sequential scan. nvme_scan_ns_list can fail for a variety of reasons,
> e.g. transient transport issue. And the resulting sequential scan can be
> extremely expensive on controllers reporting an NN value close to the
> maximum allowed (>4 billion). Avoid sequential scans wherever possible
> by only falling back to them if nvme_scan_ns_list fails due to
> controller non-support of Identify NS List.

Signed-off-by: Uday Shankar <ushankar at purestorage.com>

> ---
> This would break devices that claim to support version NVME_VS(1, 1, 0)
> or above, but don't support Identify NS List. But it looks like we
> already have NVME_QUIRK_IDENTIFY_CNS to deal with that.
> 
>  drivers/nvme/host/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 0090dc0b3ae6..5bd19819d33b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4535,7 +4535,7 @@ static void nvme_scan_work(struct work_struct *work)
>  	}
>  
>  	mutex_lock(&ctrl->scan_lock);
> -	if (nvme_scan_ns_list(ctrl) != 0)
> +	if (nvme_scan_ns_list(ctrl) == -EOPNOTSUPP)
>  		nvme_scan_ns_sequential(ctrl);
>  	mutex_unlock(&ctrl->scan_lock);
>  }
> 
> base-commit: d30a909f9bb5283e701a5fdfffac763ef57a3e7c
> -- 
> 2.25.1
>