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SubjectRe: [RFC 2/3] virtio_ring: add VIRTIO_RING_NO_LEGACY
On Fri, Dec 07, 2018 at 04:48:41PM +0800, Tiwei Bie wrote:
> Introduce VIRTIO_RING_NO_LEGACY to support disabling legacy
> macros and layout definitions.
>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
> VRING_AVAIL_ALIGN_SIZE, VRING_USED_ALIGN_SIZE and VRING_DESC_ALIGN_SIZE
> are not pre-virtio 1.0, but can also be disabled by VIRTIO_RING_NO_LEGACY
> in this patch, because their names are not consistent with other names.
> Not sure whether this is a good idea. If we want this, we may also want
> to define _SPLIT_ version for them.

I don't think it's a good idea to have alignment in there - the point of
NO_LEGACY is to help catch bugs not to sanitize coding style IMHO.

And spec calls "legacy" the 0.X interfaces, let's not muddy the waters.

>
> include/uapi/linux/virtio_ring.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 9b0c0d92ab62..192573827850 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -37,6 +37,7 @@
> #include <linux/types.h>
> #include <linux/virtio_types.h>
>
> +#ifndef VIRTIO_RING_NO_LEGACY
> /*
> * Notice: unlike other _F_ flags, below flags are defined as shifted
> * values instead of shifts for compatibility.
> @@ -51,6 +52,7 @@
> #define VRING_USED_F_NO_NOTIFY 1
> /* Same as VRING_SPLIT_AVAIL_F_NO_INTERRUPT. */
> #define VRING_AVAIL_F_NO_INTERRUPT 1
> +#endif /* VIRTIO_RING_NO_LEGACY */
>
> /* Mark a buffer as continuing via the next field in split ring. */
> #define VRING_SPLIT_DESC_F_NEXT 0
> @@ -151,6 +153,7 @@ struct vring {
> struct vring_used *used;
> };
>
> +#ifndef VIRTIO_RING_NO_LEGACY
> /* Alignment requirements for vring elements.
> * When using pre-virtio 1.0 layout, these fall out naturally.
> */
> @@ -203,6 +206,7 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
> + align - 1) & ~(align - 1))
> + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
> }
> +#endif /* VIRTIO_RING_NO_LEGACY */
>
> /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
> /* Assuming a given event_idx value from the other side, if
> --
> 2.17.1

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