[PATCH v7 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM_OWNER

[Cindy Lu <lulu@redhat.com>]

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 | 11 +++++++++++
 2 files changed, 26 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.
+
+          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.
+
+	  If unsure, say "N".
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index fb0c7fb43f78..09e5e44dc516 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 +2315,15 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 		r = 0;
 		goto done;
 	}
+
+#else
+	if (ioctl == VHOST_FORK_FROM_OWNER) {
+		/* When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is 'n', return error */
+		r = -ENOTTY;
+		goto done;
+	}
+#endif
+
 	/* You must be the owner to do anything else */
 	r = vhost_dev_check_owner(d);
 	if (r)
-- 
2.45.0