Re: [PATCH v8 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM_OWNER

Michael S. Tsirkin
2025-04-08T11:56:15Z

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@redhat.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