linux-kernel - Re: [PATCH v8 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM

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Message-ID: <20250408075426-mutt-send-email-mst@kernel.org>
Date: Tue, 8 Apr 2025 07:56:08 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: jasowang@...hat.com, michael.christie@...cle.com, sgarzare@...hat.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH v8 8/8] vhost: Add a KConfig knob to enable IOCTL
 VHOST_FORK_FROM_OWNER

On Fri, Mar 28, 2025 at 06:02:52PM +0800, Cindy Lu wrote:
> Introduce a new config knob `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL`,
> to control the availability of the `VHOST_FORK_FROM_OWNER` ioctl.
> When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set to n, the ioctl
> is disabled, and any attempt to use it will result in failure.
> 
> Signed-off-by: Cindy Lu <lulu@...hat.com>
> ---
>  drivers/vhost/Kconfig | 15 +++++++++++++++
>  drivers/vhost/vhost.c |  3 +++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index b455d9ab6f3d..e5b9dcbf31b6 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -95,3 +95,18 @@ config VHOST_CROSS_ENDIAN_LEGACY
>  	  If unsure, say "N".
>  
>  endif
> +
> +config VHOST_ENABLE_FORK_OWNER_IOCTL
> +	bool "Enable IOCTL VHOST_FORK_FROM_OWNER"
> +	default n
> +	help
> +	  This option enables the IOCTL VHOST_FORK_FROM_OWNER, which allows
> +	  userspace applications to modify the thread mode for vhost devices.

ok

> +          By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to `n`,
> +          meaning the ioctl is disabled and any operation using this ioctl
> +          will fail.
> +          When the configuration is enabled (y), the ioctl becomes
> +          available, allowing users to set the mode if needed.

no need to be so verbose - the disabled beavious belongs in commit log
not here.

Also either ioctl or IOCTL but not both.

> +
> +	  If unsure, say "N".
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index fb0c7fb43f78..568e43cb54a9 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2294,6 +2294,8 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
>  		r = vhost_dev_set_owner(d);
>  		goto done;
>  	}
> +
> +#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
>  	if (ioctl == VHOST_FORK_FROM_OWNER) {
>  		u8 inherit_owner;
>  		/*inherit_owner can only be modified before owner is set*/
> @@ -2313,6 +2315,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
>  		r = 0;
>  		goto done;
>  	}
> +#endif
>  	/* You must be the owner to do anything else */
>  	r = vhost_dev_check_owner(d);
>  	if (r)
> -- 
> 2.45.0