[PATCH v2 0/3] nvme: make core.nvme_multipath configurable

[John Meneghini <jmeneghi@redhat.com>]

These patches propose an alternative to the outright removal of the nvme
core multipath module parameter. Rather than deleting this module
parameter we control its appearance with a new Kconfig option named
NVME_MULTIPATH_PARAM

Note that the default kernel config settings produce a kernel
with no change in functionality. By default both NVME_MULTIPATH
and NVME_MULTIPATH_PARAM are enabled and there are no user visable
changes.

To remove the core.nvme_multipath parameter simply compile with
CONFIG_NVME_MULTIPATH_PARAM=n.

Note: the current behavior of nvme-v6.15

  CONFIG_NVME_MULTIPATH=y and nvme_core.multipath=N

  [  182.863531] nvme nvme4: Found shared namespace 1, but multipathing not supported.
  [  182.871030] nvme nvme4: Support for shared namespaces without CONFIG_NVME_MULTIPATH is deprecated and will be removed in Linux 6.0.

Closes: https://lore.kernel.org/linux-nvme/20241121220321.40616-1-bgurney@redhat.com/
Closes: https://lore.kernel.org/linux-nvme/20250204211158.43126-1-bgurney@redhat.com/
Closes: https://lore.kernel.org/linux-nvme/20250228032541.369804-1-jmeneghi@redhat.com/ 

Changes Since v1

Rebased patches to nvme-v6.15

  nvme: add mulitipath warning to nvme_alloc_ns

Dropped this patch because the dmesg it produced was redundant and not
needed. Testing multiport devices with CONFIG_NVME_MULTIPATH disabled
show the following console message at boot.

[167523.157284] nvme nvme5: Found shared namespace 1, but multipathing not supported.
[167523.217083] nvme nvme6: Please enable CONFIG_NVME_MULTIPATH for full support of multi-port devices.

  nvme-multipath: add the NVME_MULTIPATH_PARAM config option

Fixed up the Kconfig description for NVME_MULTIPATH_PARAM.
Add default y and tested the follow Kconfig options.

Tested the following:

  make mod2noconfig
  make allyesconfig
  make allmodconfig
  make olddefconfig
  make oldconfig - accept all defaults

No change in current behavior.

  nvme: update the multipath warning in nvme_init_ns_head

Tests ran with CONFIG_NVME_MULTIPATH=y and CONFIG_NVME_MULTIPATH_PARM=n

No change in current behavior except:

  [root@rhel-storage-108 ~]# cat /sys/module/nvme_core/parameters/multipath
  cat: /sys/module/nvme_core/parameters/multipath: No such file or directory
  
The following does nothing, just like it does when CONFIG_NVME_MULTIPATH=n

  [root@rhel-storage-108 ~]# grubby --update-kernel=ALL --args="nvme_core.multipath=N"
  [root@rhel-storage-108 ~]# reboot now
  .
  .
  .
  [root@rhel-storage-108 ~]# cat /proc/cmdline
  BOOT_IMAGE=(hd1,gpt2)/vmlinuz-6.14.0-rc2_config_ana4a+ ...  nvme_core.multipath=N
  [root@rhel-storage-108 ~]# cat /sys/module/nvme_core/parameters/multipath
  cat: /sys/module/nvme_core/parameters/multipath: No such file or directory

Tests ran with CONFIG_NVME_MULTIPATH=y and CONFIG_NVME_MULTIPATH_PARM=y

  There is no change in current behavior:

Tests ran with CONFIG_NVME_MULTIPATH=y, CONFIG_NVME_MULTIPATH_PARM=y
and nvme_core.multipath=N

  [  372.040105] nvme nvme4: Found shared namespace 1, but multipathing not supported.
  [  372.047606] nvme nvme4: Shared namespace support requires core_nvme.multipath=Y.
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
			                   new message
  [  372.105469] nvme nvme5: creating 2 I/O queues.
  [  372.110383] nvme nvme5: mapped 2/0/0 default/read/poll queues.
  [  372.125480] nvme nvme5: new ctrl: NQN ....
  [  372.166081] nvme nvme5: Found shared namespace 1, but multipathing not supported.
  [  372.235964] nvme nvme6: creating 2 I/O queues.
  [  372.240926] nvme nvme6: mapped 2/0/0 default/read/poll queues.
  [  372.255964] nvme nvme6: new ctrl: NQN ....
  [root@rhel-storage-108 ~]# cat /sys/module/nvme_core/parameters/multipath
  N
  [root@rhel-storage-108 ~]# grubby --remove-args="nvme_core.multipath=N" --update-kernel=ALL
  [root@rhel-storage-108 ~]# grubby --info=ALL | grep nvme_core 
  [root@rhel-storage-108 ~]# reboot now
  .
  .
  .
  [root@rhel-storage-108 ~]# cat /sys/module/nvme_core/parameters/multipath
  Y



John Meneghini (3):
  nvme-multipath: change the NVME_MULTIPATH config option
  nvme-multipath: add the NVME_MULTIPATH_PARAM config option
  nvme: update the multipath warning in nvme_init_ns_head

 drivers/nvme/host/Kconfig     | 26 ++++++++++++++++++++++----
 drivers/nvme/host/core.c      |  2 +-
 drivers/nvme/host/multipath.c |  3 ++-
 3 files changed, 25 insertions(+), 6 deletions(-)

-- 
2.48.1