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

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Message-ID: <CACGkMEuEyXC7pOfwUTKSSrc-vrGW-v7SucV0qAHDE5Lo-b7zYA@mail.gmail.com>
Date: Tue, 5 Nov 2024 17:39:44 +0800
From: Jason Wang <jasowang@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: mst@...hat.com, michael.christie@...cle.com, sgarzare@...hat.com, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v3 7/9] vhost: Add new UAPI to support change to task mode

On Tue, Nov 5, 2024 at 3:28 PM Cindy Lu <lulu@...hat.com> wrote:
>
> 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@...hat.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;

Is there any case that we need to switch from owner back to kthread?
If not I would choose a more simplified API that is just
VHOST_INHERIT_OWNER.

>         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

Thanks

>