linux-kernel - Re: [PATCH v3 3/5] nvme: add the NVME_ENABLE_MULTIPATH

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Message-ID: <CADUfDZoXg39h-5gi+aVj2u1H6HC4Beyp2XPTrjJ_PMDPf11dQg@mail.gmail.com>
Date: Fri, 28 Mar 2025 12:49:37 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: John Meneghini <jmeneghi@...hat.com>
Cc: kbusch@...nel.org, hch@....de, sagi@...mberg.me, loberman@...hat.com, 
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	emilne@...hat.com, bgurney@...hat.com
Subject: Re: [PATCH v3 3/5] nvme: add the NVME_ENABLE_MULTIPATH_PARAM config option

On Fri, Mar 28, 2025 at 12:42 PM John Meneghini <jmeneghi@...hat.com> wrote:
>
> The CONFIG_NVME_ENABLE_MULTIPATH_PARAM option controls the
> core_nvme.multipath parameter. When CONFIG_NVME_ENABLE_MULTIPATH_PARAM=n
> the multipath parameter is removed from the kernel and nvme multipathing
> is permanently enabled.  When CONFIG_NVME_ENABLE_MULTIPATH_PARAM=y the
> nvme multipath parameter is added to the kernel and nvme multipath
> support is controlled by the core_nvme.multipath parameter.
>
> By default CONFIG_NVME_ENABLE_MULTIPATH_PARAM=y
>
> Signed-off-by: John Meneghini <jmeneghi@...hat.com>
> Tested-by: John Meneghini <jmeneghi@...hat.com>
> Reviewed-by: Bryan Gurney <bgurney@...hat.com>
> ---
>  drivers/nvme/host/Kconfig     | 11 +++++++++++
>  drivers/nvme/host/multipath.c |  2 ++
>  2 files changed, 13 insertions(+)
>
> diff --git a/drivers/nvme/host/Kconfig b/drivers/nvme/host/Kconfig
> index d47dfa80fb95..8c04b6b93982 100644
> --- a/drivers/nvme/host/Kconfig
> +++ b/drivers/nvme/host/Kconfig
> @@ -28,6 +28,17 @@ config NVME_MULTIPATH
>
>           If unsure, say Y.
>
> +config NVME_ENABLE_MULTIPATH_PARAM
> +       bool "NVMe enable multipath param"
> +       depends on NVME_CORE && NVME_MULTIPATH
> +       default y
> +       help
> +         This option enables the core_nvme.multipath parameter.
> +         If this option is disabled the core_nvme.multipath parameter
> +         is excluded from the kernel.
> +
> +         If unsure, say Y.
> +
>  config NVME_VERBOSE_ERRORS
>         bool "NVMe verbose error reporting"
>         depends on NVME_CORE
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 6b12ca80aa27..83084093e8db 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -10,9 +10,11 @@
>  #include "nvme.h"
>
>  bool multipath = true;
> +#ifdef CONFIG_NVME_ENABLE_MULTIPATH_PARAM
>  module_param(multipath, bool, 0444);
>  MODULE_PARM_DESC(multipath,
>         "turn on native support for multiple controllers per subsystem");
> +#endif

If CONFIG_NVME_ENABLE_MULTIPATH_PARAM is disabled, could you #define
multipath false in place of the global variable? That would allow the
compiler to optimize out the multipath checks and the resulting dead
code.

Best,
Caleb