linux-kernel - Re: [PATCH 3/6] virtio: allow extra context per descriptor

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Message-Id: <20170330092316.2a25e4f1.cornelia.huck@de.ibm.com>
Date:   Thu, 30 Mar 2017 09:23:16 +0200
From:   Cornelia Huck <cornelia.huck@...ibm.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 3/6] virtio: allow extra context per descriptor

On Wed, 29 Mar 2017 23:48:53 +0300
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> Allow extra context per descriptor. To avoid slow down for data path,
> this disables use of indirect descriptors for this vq.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/virtio/virtio_ring.c | 70 ++++++++++++++++++++++++++++++++++++--------
>  include/linux/virtio.h       |  9 ++++++
>  2 files changed, 66 insertions(+), 13 deletions(-)
> 

>  /**
> + * virtqueue_add_inbuf_ctx - expose input buffers to other end
> + * @vq: the struct virtqueue we're talking about.
> + * @sg: scatterlist (must be well-formed and terminated!)
> + * @num: the number of entries in @sg writable by other side
> + * @data: the token identifying the buffer.
> + * @ctx: extra context for the token

I think that needs do that ctx != NULL collides with indirect
descriptors.

> + * @gfp: how to do memory allocations (if necessary).
> + *
> + * Caller must ensure we don't call this with other virtqueue operations
> + * at the same time (except where noted).
> + *
> + * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
> + */
> +int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
> +			struct scatterlist *sg, unsigned int num,
> +			void *data,
> +			void *ctx,
> +			gfp_t gfp)
> +{
> +	return virtqueue_add(vq, &sg, num, 0, 1, data, ctx, gfp);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);