linux-kernel - Re: [PATCH v2] virtio: add VIRTIO_RING_NO

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Message-ID: <20190911052825-mutt-send-email-mst@kernel.org>
Date:   Wed, 11 Sep 2019 05:29:50 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Matej Genci <matej.genci@...anix.com>
Cc:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] virtio: add VIRTIO_RING_NO_LEGACY

On Tue, Sep 10, 2019 at 05:53:44PM +0000, Matej Genci wrote:
> Add macro to disable legacy functions vring_init and vring_size.
> 
> Signed-off-by: Matej Genci <matej.genci@...anix.com>
> ---
> 
> V2: Put all legacy APIs inside guards.
> 
> ---
>  include/uapi/linux/virtio_ring.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 4c4e24c291a5..efe5a421b4ea 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -118,6 +118,8 @@ struct vring_used {
>  	struct vring_used_elem ring[];
>  };
>  
> +#ifndef VIRTIO_RING_NO_LEGACY
> +
>  struct vring {
>  	unsigned int num;
>  
> @@ -128,6 +130,8 @@ struct vring {
>  	struct vring_used *used;
>  };
>  
> +#endif /* VIRTIO_RING_NO_LEGACY */
> +
>  /* Alignment requirements for vring elements.
>   * When using pre-virtio 1.0 layout, these fall out naturally.
>   */
> @@ -135,6 +139,8 @@ struct vring {
>  #define VRING_USED_ALIGN_SIZE 4
>  #define VRING_DESC_ALIGN_SIZE 16
>  
> +#ifndef VIRTIO_RING_NO_LEGACY
> +
>  /* The standard layout for the ring is a continuous chunk of memory which looks
>   * like this.  We assume num is a power of 2.
>   *
> @@ -195,6 +201,8 @@ static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
>  	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
>  }
>  
> +#endif /* VIRTIO_RING_NO_LEGACY */
> +
>  struct vring_packed_desc_event {
>  	/* Descriptor Ring Change Event Offset/Wrap Counter. */
>  	__le16 off_wrap;

OK almost but vring_need_event is actually useful for all variants
so should be outside the guards :) Sorry about it.

-- 
MST