Re: [RFC 2/3] virtio_ring: add VIRTIO_RING_NO_LEGACY
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2018-12-07 18:05:35
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 <redacted> --- 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.
quoted hunk
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