[RFC PATCH 2/2] nvme-multipath: remove multipath module param

[John Meneghini]

On 3/21/25 2:37 AM, Nilay Shroff wrote:
> Remove the multipath module parameter from nvme-core and make native
> NVMe multipath support explicit. Since we now always create a multipath
> head disk node, even for single-port NVMe disks, when CONFIG_NVME_
> MULTIPATH is enabled, this module parameter is no longer needed to
> toggle the behavior.
> 
> Users who prefer non-native multipath must disable CONFIG_NVME_MULTIPATH
> at compile time.

This patch is not needed if you use my patch at:

https://lore.kernel.org/linux-nvme/20250322232848.225140-1-jmeneghi@redhat.com/T/#m7a6ea63be64731f19df4e17fda7db2b18d8551c7
  
> Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
> ---
>   drivers/nvme/host/core.c      | 18 +++++++-----------
>   drivers/nvme/host/multipath.c | 17 ++---------------
>   drivers/nvme/host/nvme.h      |  1 -
>   3 files changed, 9 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index e798809a8325..50c170425141 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3823,14 +3823,13 @@ static int nvme_init_ns_head(struct nvme_ns *ns, struct nvme_ns_info *info)
>   					info->nsid);
>   			goto out_put_ns_head;
>   		}
> -
> -		if (!multipath) {
> -			dev_warn(ctrl->device,
> -				"Found shared namespace %d, but multipathing not supported.\n",
> -				info->nsid);
> -			dev_warn_once(ctrl->device,
> -				"Support for shared namespaces without CONFIG_NVME_MULTIPATH is deprecated and will be removed in Linux 6.0.\n");
> -		}
> +#ifndef CONFIG_NVME_MULTIPATH
> +		dev_warn(ctrl->device,
> +			"Found shared namespace %d, but multipathing not supported.\n",
> +			info->nsid);
> +		dev_warn_once(ctrl->device,
> +			"Support for shared namespaces without CONFIG_NVME_MULTIPATH is deprecated and will be removed in Linux 6.0.\n");

I think this message needs to change.  See my patch at:

https://lore.kernel.org/linux-nvme/20250322232848.225140-1-jmeneghi@redhat.com/T/#md2f1d9706f4cbeb8bd53e562d1036195c0599fe1

> +#endif
>   	}
>   
>   	list_add_tail_rcu(&ns->siblings, &head->list);
> @@ -3929,9 +3928,6 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
>   		sprintf(disk->disk_name, "nvme%dc%dn%d", ctrl->subsys->instance,
>   			ctrl->instance, ns->head->instance);
>   		disk->flags |= GENHD_FL_HIDDEN;
> -	} else if (multipath) {
> -		sprintf(disk->disk_name, "nvme%dn%d", ctrl->subsys->instance,
> -			ns->head->instance);

I don't think we should remove the 'multipath' variable here we just need to control the users ability
to change it.

>   	} else {
>   		sprintf(disk->disk_name, "nvme%dn%d", ctrl->instance,
>   			ns->head->instance);
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 0f54889bd483..84211f64d178 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -9,11 +9,6 @@
>   #include <trace/events/block.h>
>   #include "nvme.h"
>   
> -bool multipath = true;
> -module_param(multipath, bool, 0444);
> -MODULE_PARM_DESC(multipath,
> -	"turn on native support for multiple controllers per subsystem");
> -
>   static const char *nvme_iopolicy_names[] = {
>   	[NVME_IOPOLICY_NUMA]	= "numa",
>   	[NVME_IOPOLICY_RR]	= "round-robin",
> @@ -671,14 +666,6 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
>   	INIT_DELAYED_WORK(&head->remove_work, nvme_remove_head_work);
>   	head->delayed_shutdown_sec = 0;
>   
> -	/*
> -	 * A head disk node is always created for all types of NVMe disks
> -	 * (single-ported and multi-ported), unless the multipath module
> -	 * parameter is explicitly set to false.
> -	 */
> -	if (!multipath)
> -		return 0;
> -
>   	blk_set_stacking_limits(&lim);
>   	lim.dma_alignment = 3;
>   	lim.features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL;
> @@ -1262,8 +1249,8 @@ int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>   	size_t ana_log_size;
>   	int error = 0;
>   
> -	/* check if multipath is enabled and we have the capability */
> -	if (!multipath || !ctrl->subsys ||
> +	/* check if controller has ANA capability */
> +	if (!ctrl->subsys ||
>   	    !(ctrl->subsys->cmic & NVME_CTRL_CMIC_ANA))
>   		return 0;
>   
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 4375357b8cd7..fba686b91976 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -997,7 +997,6 @@ static inline bool nvme_disk_is_ns_head(struct gendisk *disk)
>   	return disk->fops == &nvme_ns_head_ops;
>   }
>   #else
> -#define multipath false
>   static inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
>   {
>   	return false;