[dpdk-dev] [PATCH] vhost: add API for getting last_idx of vrings

[Tomasz Kulasek <tomaszx.kulasek@intel.com>]

vhost-net devices might keep track of last descriptors indices by
themselves, and assuming they initially start at 0, but that is not the
case for vhost-scsi. Initial last descriptor indices are set via
VHOST_USER_SET_VRING_BASE message, and we cannot possibly predict what
will they be. Setting these to vqueue->used->idx is also not an option,
because there might be some yet unprocessed requests between these and
the actual last_idx. This patch adds API for getting/setting last
descriptor indices of vrings, so that they can be synchronized between
user-device and rte_vhost.

The last_idx flow could be as following:

 * vhost start,
 * received SET_VRING_BASE msg, last_idx is set on rte_vhost side,
 * created user-device, last_idx pulled from rte_vhost,
 * requests are being processed by user-device, last_idx changes,
 * destroyed user-device, last_idx pushed to rte_vhost,
 * at this point, vrings could be recreated and another SET_VRING_BASE
   message could arrive, so last_idx would be set
 * recreated user-device, last_idx pulled from rte_vhost.


Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
---
 lib/librte_vhost/rte_vhost.h | 24 ++++++++++++++++++++++++
 lib/librte_vhost/vhost.c     | 27 +++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index d33206997..b9ba058d1 100644
--- a/lib/librte_vhost/rte_vhost.h
+++ b/lib/librte_vhost/rte_vhost.h
@@ -62,6 +62,9 @@ struct rte_vhost_vring {
 
 	int			kickfd;
 	uint16_t		size;
+
+	uint16_t		last_avail_idx;
+	uint16_t		last_used_idx;
 };
 
 /**
@@ -434,6 +437,27 @@ int rte_vhost_vring_call(int vid, uint16_t vring_idx);
  */
 uint32_t rte_vhost_rx_queue_count(int vid, uint16_t qid);
 
+/**
+ * Set id of the last descriptors in avail and used guest vrings.
+ *
+ * In case user application operates directly on buffers, it should use this
+ * function on device destruction to retrieve the same values later on in device
+ * creation via rte_vhost_get_vhost_vring(int, uint16_t, struct rte_vhost_vring *)
+ *
+ * @param vid
+ *  vhost device ID
+ * @param vring_idx
+ *  vring index
+ * @param last_avail_idx
+ *  id of the last descriptor in avail ring to be set
+ * @param last_used_idx
+ *  id of the last descriptor in used ring to be set
+ * @return
+ *  0 on success, -1 on failure
+ */
+int rte_vhost_set_vhost_vring_last_idx(int vid, uint16_t vring_idx,
+			      uint16_t last_avail_idx, uint16_t last_used_idx);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index a407067e2..a82dc5a62 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -512,6 +512,9 @@ rte_vhost_get_vhost_vring(int vid, uint16_t vring_idx,
 	vring->kickfd  = vq->kickfd;
 	vring->size    = vq->size;
 
+	vring->last_avail_idx = vq->last_avail_idx;
+	vring->last_used_idx = vq->last_used_idx;
+
 	return 0;
 }
 
@@ -627,3 +630,27 @@ rte_vhost_rx_queue_count(int vid, uint16_t qid)
 
 	return *((volatile uint16_t *)&vq->avail->idx) - vq->last_avail_idx;
 }
+
+int
+rte_vhost_set_vhost_vring_last_idx(int vid, uint16_t vring_idx,
+			      uint16_t last_avail_idx, uint16_t last_used_idx)
+{
+	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
+
+	dev = get_device(vid);
+	if (!dev)
+		return -1;
+
+	if (vring_idx >= VHOST_MAX_VRING)
+		return -1;
+
+	vq = dev->virtqueue[vring_idx];
+	if (!vq)
+		return -1;
+
+	vq->last_avail_idx = last_avail_idx;
+	vq->last_used_idx = last_used_idx;
+
+	return 0;
+}
-- 
2.14.1