[PATCH v11 1/3] vhost: Add a new parameter in vhost_dev to allow user select kthread

[Cindy Lu <lulu@redhat.com>]

The vhost now uses vhost_task and workers as a child of the owner thread.
While this aligns with containerization principles, it confuses some
legacy userspace applications, therefore, we are reintroducing kthread
API support.

Introduce a new parameter to enable users to choose between kthread and
task mode.

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c |  2 ++
 drivers/vhost/vhost.h | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5ebb973dba..ff3052858308 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -41,6 +41,7 @@ static int max_iotlb_entries = 2048;
 module_param(max_iotlb_entries, int, 0444);
 MODULE_PARM_DESC(max_iotlb_entries,
 	"Maximum number of iotlb entries. (default: 2048)");
+static bool fork_from_owner_default = true;
 
 enum {
 	VHOST_MEMORY_F_LOG = 0x1,
@@ -552,6 +553,7 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->byte_weight = byte_weight;
 	dev->use_worker = use_worker;
 	dev->msg_handler = msg_handler;
+	dev->fork_owner = fork_from_owner_default;
 	init_waitqueue_head(&dev->wait);
 	INIT_LIST_HEAD(&dev->read_list);
 	INIT_LIST_HEAD(&dev->pending_list);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index bb75a292d50c..e3d4732883af 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -176,6 +176,16 @@ struct vhost_dev {
 	int byte_weight;
 	struct xarray worker_xa;
 	bool use_worker;
+	/*
+	 * If fork_owner is true we use vhost_tasks to create
+	 * the worker so all settings/limits like cgroups, NPROC,
+	 * scheduler, etc are inherited from the owner. If false,
+	 * we use kthreads and only attach to the same cgroups
+	 * as the owner for compat with older kernels.
+	 * here we use true as default value.
+	 * The default value is set by fork_from_owner_default
+	 */
+	bool fork_owner;
 	int (*msg_handler)(struct vhost_dev *dev, u32 asid,
 			   struct vhost_iotlb_msg *msg);
 };
-- 
2.45.0