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

[Stefano Garzarella]

On Tue, Nov 05, 2024 at 03:25:26PM +0800, Cindy Lu 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@xxxxxxxxxx>
> ---
> 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;

I don't know if something is missing in this patch, but I am confused:

`r` is set few lines below...

> 	int i, fd;
> +	bool inherit_owner;
>
> 	/* If you are not the owner, you can become one */
> 	if (ioctl == VHOST_SET_OWNER) {
...

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

So, why we are now initializing it to 0?

> @@ -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))

And here, how this check can be false, if at the beginning of the
function we call vhost_dev_check_owner()?

Maybe your intention was to add this code before the
`vhost_dev_check_owner()` call, so this should explain why initialize
`r` to 0, but I'm not sure.

> +			break;

Should we return an error (e.g. -EPERM) in this case?

> +
> +		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)
> +

Please add a documentation here, this is UAPI, so the user should
know what this ioctl does based on the parameter.

Thanks,
Stefano

> +#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, bool)
> #endif
> --
> 2.45.0