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

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Message-ID: <3zmkrimo2nghk42iatj4tuhfb7qrxx235srleuavi4at5dsv26@zj6wqgj7hj62>
Date: Tue, 1 Apr 2025 15:21:41 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: jasowang@...hat.com, mst@...hat.com, michael.christie@...cle.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(+)

IMHO this patch should be squashed with "[PATCH v8 6/8] vhost: uapi to
control task mode (owner vs kthread)".

It might break the bisection to support an ioctl, and after a few
commits enable or disable it depending on a kernel configuration.

>
>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

nit: there is a mix of tabs and spaces in the next block, should we
fix it?

>+
>+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.
   ^
   tabs

>+
>+          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.
   ^
   spaces
>+
>+	  If unsure, say "N".
   ^
   tabs

>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
>