On Thu, Jan 2, 2025 at 11:37 AM Jason Wang [off-list ref] wrote:

On Mon, Dec 30, 2024 at 8:45 PM Cindy Lu [off-list ref] wrote:

quoted

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 <redacted>
---
 drivers/vhost/vhost.c      | 22 +++++++++++++++++++++-
 include/uapi/linux/vhost.h | 19 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ff17c42e2d1a..47c1329360ac 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2250,15 +2250,35 @@ 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;
+       u8 inherit_owner;

        /* If you are not the owner, you can become one */
        if (ioctl == VHOST_SET_OWNER) {
                r = vhost_dev_set_owner(d);
                goto done;
        }
+       if (ioctl == VHOST_SET_INHERIT_FROM_OWNER) {
+               /*inherit_owner can only be modified before owner is set*/
+               if (vhost_dev_has_owner(d)) {
+                       r = -EBUSY;
+                       goto done;
+               }
+               if (copy_from_user(&inherit_owner, argp, sizeof(u8))) {
+                       r = -EFAULT;
+                       goto done;
+               }

Not a native speaker but I wonder if "VHOST_FORK_FROM_OWNER" is better or not.

Sure will do

quoted

+               /* Validate the inherit_owner value, ensuring it is either 0 or 1 */
+               if (inherit_owner > 1) {
+                       r = -EINVAL;
+                       goto done;
+               }
+
+               d->inherit_owner = (bool)inherit_owner;

So this allows userspace to reset the owner and toggle the value. This
seems to be fine, but I wonder if we need to some cleanup in
vhost_dev_reset_owner() or not. Let's explain this somewhere (probably
in the commit log).

sure will add these information
Thanks
Cindy

quoted

+               goto done;
+       }
        /* You must be the owner to do anything else */
        r = vhost_dev_check_owner(d);
        if (r)

diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b95dd84eef2d..f5fcf0b25736 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h

@@ -235,4 +235,23 @@
  */
 #define VHOST_VDPA_GET_VRING_SIZE      _IOWR(VHOST_VIRTIO, 0x82,       \
                                              struct vhost_vring_state)
+
+/**
+ * VHOST_SET_INHERIT_FROM_OWNER - Set the inherit_owner flag for the vhost device
+ *
+ * @param inherit_owner: An 8-bit value that determines the vhost thread mode
+ *
+ * When inherit_owner is set to 1 (default behavior):
+ *   - The VHOST worker threads inherit their values/checks from
+ *     the thread that owns the VHOST device. The vhost threads will
+ *     be counted in the nproc rlimits.
+ *
+ * When inherit_owner is set to 0:
+ *   - The VHOST worker threads will use the traditional kernel thread (kthread)
+ *     implementation, which may be preferred by older userspace applications that
+ *     do not utilize the newer vhost_task concept.
+ */
+
+#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
 #endif
--

2.45.0

Thanks