[PATCH v3 7/9] vhost: Add new UAPI to support change to task mode

[Cindy Lu <lulu@redhat.com>]

Add a new UAPI to enable setting the vhost device to task mode.
The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
to configure the mode if necessary.
This setting must be applied before VHOST_SET_OWNER, as the worker
will be created in the VHOST_SET_OWNER function

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c      | 15 ++++++++++++++-
 include/uapi/linux/vhost.h |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c17dc01febcc..70c793b63905 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2274,8 +2274,9 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
 	struct eventfd_ctx *ctx;
 	u64 p;
-	long r;
+	long r = 0;
 	int i, fd;
+	bool inherit_owner;
 
 	/* If you are not the owner, you can become one */
 	if (ioctl == VHOST_SET_OWNER) {
@@ -2332,6 +2333,18 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 		if (ctx)
 			eventfd_ctx_put(ctx);
 		break;
+	case VHOST_SET_INHERIT_FROM_OWNER:
+		/*inherit_owner can only be modified before owner is set*/
+		if (vhost_dev_has_owner(d))
+			break;
+
+		if (copy_from_user(&inherit_owner, argp,
+				   sizeof(inherit_owner))) {
+			r = -EFAULT;
+			break;
+		}
+		d->inherit_owner = inherit_owner;
+		break;
 	default:
 		r = -ENOIOCTLCMD;
 		break;
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b95dd84eef2d..1e192038633d 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,6 @@
  */
 #define VHOST_VDPA_GET_VRING_SIZE	_IOWR(VHOST_VIRTIO, 0x82,	\
 					      struct vhost_vring_state)
+
+#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, bool)
 #endif
-- 
2.45.0