On Mon, Jun 11, 2018 at 11:18:59AM -0400, nilal@xxxxxxxxxx wrote:
> From: Nitesh Narayan Lal <nilal@xxxxxxxxxx>
>
> This patch enables the driver to expose a chain of buffers to the
> other end using vring descriptor followed by a kick. After which it
> busy waits till the update is done.
>
> Signed-off-by: Nitesh Narayan Lal <nilal@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_ring.c | 157 ++++++++++++++++++++++++++++++++++++++++++-
> include/linux/virtio.h | 19 ++++++
> 2 files changed, 175 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 21d464a..586dd62 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -435,6 +435,136 @@ static inline int virtqueue_add(struct virtqueue *_vq,
> }
>
> /**
> + * virtqueue_add_chain - expose a chain of buffers to the other end
> + * @_vq: the struct virtqueue we're talking about.
> + * @head: desc id of the chain head.
> + * @indirect: set if the chain of descs are indrect descs.
> + * @indir_desc: the first indirect desc.
> + * @data: the token identifying the chain.
> + * @ctx: extra context for the token.
> + *
> + * 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_chain(struct virtqueue *_vq,
> + unsigned int head,
> + bool indirect,
> + struct vring_desc *indir_desc,
> + void *data,
> + void *ctx)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> +
> + /* The desc chain is empty. */
> + if (head == VIRTQUEUE_DESC_ID_INIT)
> + return 0;
> +
> + START_USE(vq);
> +
> + if (unlikely(vq->broken)) {
> + END_USE(vq);
> + return -EIO;
> + }
> +
> + /* This is the data for callback, in our case may not be required. */
> + vq->desc_state[head].data = data;
> + if (indirect)
> + vq->desc_state[head].indir_desc = indir_desc;
> + if (ctx)
> + vq->desc_state[head].indir_desc = ctx;
> +
> + vq->avail_idx_shadow = 1;
> + vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev, vq->avail_idx_shadow);
> + vq->num_added = 1;
> + END_USE(vq);
> + virtqueue_kick_sync(_vq);
I dislike the kick_sync being called internally.
IMHO it's preferable to have callers invoke it
as appropriate.
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_add_chain);
> +
> +/**
> + * virtqueue_add_chain_desc - add a buffer to a chain using a vring desc
> + * @vq: the struct virtqueue we're talking about.
> + * @addr: address of the buffer to add.
> + * @len: length of the buffer.
> + * @head_id: desc id of the chain head.
> + * @prev_id: desc id of the previous buffer.
> + * @in: set if the buffer is for the device to write.
> + *
> + * 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_chain_desc(struct virtqueue *_vq,
> + u64 addr,
> + u32 len,
> + unsigned int *head_id,
> + unsigned int *prev_id,
> + bool in)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> + struct vring_desc *desc = vq->vring.desc;
> + u16 flags = in ? VRING_DESC_F_WRITE : 0;
> + unsigned int i;
> +
> + /* Sanity check */
> + if (!_vq || !head_id || !prev_id)
> + return -EINVAL;
> +retry:
> + START_USE(vq);
> + if (unlikely(vq->broken)) {
> + END_USE(vq);
> + return -EIO;
> + }
> +
> + if (vq->vq.num_free < 1) {
> + /*
> + * If there is no desc avail in the vq, so kick what is
> + * already added, and re-start to build a new chain for
> + * the passed sg.
> + */
> + if (likely(*head_id != VIRTQUEUE_DESC_ID_INIT)) {
> + END_USE(vq);
> + virtqueue_add_chain(_vq, *head_id, 0, NULL, vq, NULL);
> + virtqueue_kick_sync(_vq);
> + *head_id = VIRTQUEUE_DESC_ID_INIT;
> + *prev_id = VIRTQUEUE_DESC_ID_INIT;
> + goto retry;
> + } else {
> + END_USE(vq);
> + return -ENOSPC;
> + }
> + }
> +
> + i = vq->free_head;
> + flags &= ~VRING_DESC_F_NEXT;
> + desc[i].flags = cpu_to_virtio16(_vq->vdev, flags);
> + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
> + desc[i].len = cpu_to_virtio32(_vq->vdev, len);
> +
> + /* Add the desc to the end of the chain */
> + if (*prev_id != VIRTQUEUE_DESC_ID_INIT) {
> + desc[*prev_id].next = cpu_to_virtio16(_vq->vdev, i);
> + desc[*prev_id].flags |= cpu_to_virtio16(_vq->vdev,
> + VRING_DESC_F_NEXT);
> + }
> + *prev_id = i;
> + if (*head_id == VIRTQUEUE_DESC_ID_INIT)
> + *head_id = *prev_id;
> +
> + vq->vq.num_free--;
> + vq->free_head = virtio16_to_cpu(_vq->vdev, desc[i].next);
> + END_USE(vq);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_add_chain_desc);
> +
> +/**
> * virtqueue_add_sgs - expose buffers to other end
> * @vq: the struct virtqueue we're talking about.
> * @sgs: array of terminated scatterlists.
> @@ -556,7 +686,6 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
> START_USE(vq);
> /* We need to expose available array entries before checking avail
> * event. */
> - virtio_mb(vq->weak_barriers);
>
> old = vq->avail_idx_shadow - vq->num_added;
> new = vq->avail_idx_shadow;
> @@ -606,6 +735,32 @@ bool virtqueue_notify(struct virtqueue *_vq)
> EXPORT_SYMBOL_GPL(virtqueue_notify);
>
> /**
> + * virtqueue_kick_sync - update after add_buf and busy wait till update is done
> + * @vq: the struct virtqueue
> + *
> + * After one or more virtqueue_add_* calls, invoke this to kick
> + * the other side. Busy wait till the other side is done with the update.
> + *
> + * Caller must ensure we don't call this with other virtqueue
> + * operations at the same time (except where noted).
> + *
> + * Returns false if kick failed, otherwise true.
> + */
> +bool virtqueue_kick_sync(struct virtqueue *vq)
> +{
> + u32 len;
> +
> + if (likely(virtqueue_kick(vq))) {
> + while (!virtqueue_get_buf(vq, &len) &&
> + !virtqueue_is_broken(vq))
> + cpu_relax();
> + return true;
> + }
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_kick_sync);
> +
> +/**
> * virtqueue_kick - update after add_buf
> * @vq: the struct virtqueue
> *
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index fa1b5da..0e33630 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -57,6 +57,25 @@ int virtqueue_add_sgs(struct virtqueue *vq,
> unsigned int in_sgs,
> void *data,
> gfp_t gfp);
> +/* A desc with this init id is treated as an invalid desc */
> +#define VIRTQUEUE_DESC_ID_INIT UINT_MAX
> +int virtqueue_add_chain_desc(struct virtqueue *_vq,
> + u64 addr,
> + u32 len,
> + unsigned int *head_id,
> + unsigned int *prev_id,
> + bool in);
> +
> +int virtqueue_add_chain(struct virtqueue *_vq,
> + unsigned int head,
> + bool indirect,
> + struct vring_desc *indirect_desc,
> + void *data,
> + void *ctx);
> +
> +bool virtqueue_kick_sync(struct virtqueue *vq);
> +
> +bool virtqueue_kick_async(struct virtqueue *vq, wait_queue_head_t wq);
>
> bool virtqueue_kick(struct virtqueue *vq);
>
> --
> 2.9.5
