Re: [RFC 1/4] vDPA/ifcvf: add get/set_vq_endian support for vDPA

[Jason Wang <jasowang@redhat.com>]

在 2022/9/1 18:15, Zhu Lingshan 写道:
> This commit introuduces new config operatoions for vDPA:
> vdpa_config_ops.get_vq_endian: set vq endian-ness
> vdpa_config_ops.set_vq_endian: get vq endian-ness
>
> Because the endian-ness is a device wide attribute,
> so seting a vq's endian-ness will result in changing
> the device endian-ness, including all vqs and the config space.
>
> These two operations are implemented in ifcvf in this commit.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>   drivers/vdpa/ifcvf/ifcvf_base.h |  1 +
>   drivers/vdpa/ifcvf/ifcvf_main.c | 15 +++++++++++++++
>   include/linux/vdpa.h            | 13 +++++++++++++
>   3 files changed, 29 insertions(+)
>
> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.h b/drivers/vdpa/ifcvf/ifcvf_base.h
> index f5563f665cc6..640238b95033 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_base.h
> +++ b/drivers/vdpa/ifcvf/ifcvf_base.h
> @@ -19,6 +19,7 @@
>   #include <uapi/linux/virtio_blk.h>
>   #include <uapi/linux/virtio_config.h>
>   #include <uapi/linux/virtio_pci.h>
> +#include <uapi/linux/vhost.h>
>   
>   #define N3000_DEVICE_ID		0x1041
>   #define N3000_SUBSYS_DEVICE_ID	0x001A
> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c b/drivers/vdpa/ifcvf/ifcvf_main.c
> index f9c0044c6442..270637d0f3a5 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
> @@ -684,6 +684,19 @@ static struct vdpa_notification_area ifcvf_get_vq_notification(struct vdpa_devic
>   	return area;
>   }
>   
> +static u8 ifcvf_vdpa_get_vq_endian(struct vdpa_device *vdpa_dev, u16 idx)
> +{
> +	return VHOST_VRING_LITTLE_ENDIAN;
> +}
> +
> +static int ifcvf_vdpa_set_vq_endian(struct vdpa_device *vdpa_dev, u16 idx, u8 endian)
> +{
> +	if (endian != VHOST_VRING_LITTLE_ENDIAN)
> +		return -EFAULT;


I'm worrying that this basically make the proposed API not much useful.

For example, what would userspace do if it meet this failure?

Thanks


> +
> +	return 0;
> +}
> +
>   /*
>    * IFCVF currently doesn't have on-chip IOMMU, so not
>    * implemented set_map()/dma_map()/dma_unmap()
> @@ -715,6 +728,8 @@ static const struct vdpa_config_ops ifc_vdpa_ops = {
>   	.set_config	= ifcvf_vdpa_set_config,
>   	.set_config_cb  = ifcvf_vdpa_set_config_cb,
>   	.get_vq_notification = ifcvf_get_vq_notification,
> +	.get_vq_endian	= ifcvf_vdpa_get_vq_endian,
> +	.set_vq_endian	= ifcvf_vdpa_set_vq_endian,
>   };
>   
>   static struct virtio_device_id id_table_net[] = {
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index d282f464d2f1..5eb83453ba86 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -174,6 +174,17 @@ struct vdpa_map_file {
>    *				@idx: virtqueue index
>    *				Returns int: irq number of a virtqueue,
>    *				negative number if no irq assigned.
> + * @set_vq_endian:		set endian-ness for a virtqueue
> + *				@vdev: vdpa device
> + *				@idx: virtqueue index
> + *				@endian: the endian-ness to set,
> + *				can be VHOST_VRING_LITTLE_ENDIAN or VHOST_VRING_BIG_ENDIAN
> + *				Returns integer: success (0) or error (< 0)
> + * @get_vq_endian:		get the endian-ness of a virtqueue
> + *				@vdev: vdpa device
> + *				@idx: virtqueue index
> + *				Returns u8, the endian-ness of the virtqueue,
> + *				can be VHOST_VRING_LITTLE_ENDIAN or VHOST_VRING_BIG_ENDIAN
>    * @get_vq_align:		Get the virtqueue align requirement
>    *				for the device
>    *				@vdev: vdpa device
> @@ -306,6 +317,8 @@ struct vdpa_config_ops {
>   	(*get_vq_notification)(struct vdpa_device *vdev, u16 idx);
>   	/* vq irq is not expected to be changed once DRIVER_OK is set */
>   	int (*get_vq_irq)(struct vdpa_device *vdev, u16 idx);
> +	int (*set_vq_endian)(struct vdpa_device *vdev, u16 idx, u8 endian);
> +	u8 (*get_vq_endian)(struct vdpa_device *vdev, u16 idx);
>   
>   	/* Device ops */
>   	u32 (*get_vq_align)(struct vdpa_device *vdev);

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