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);
+
+ 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
