[PATCH 4/8] vhost-user: introduce vhost_reset_vring() interface

[Kangjie Xu]

Introduce the interface vhost_reset_vring(). The interface is a wrapper
to send a VHOST_USER_RESET_VRING message to the back-end. It will reset
an individual vring in the back-end. Meanwhile, it will wait for a reply
to ensure the reset has been completed.

Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 hw/virtio/vhost-user.c            | 41 +++++++++++++++++++++++++++++++
 include/hw/virtio/vhost-backend.h |  3 +++
 2 files changed, 44 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 3f140d5085..b49076fdc4 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -126,6 +126,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_MAX_MEM_SLOTS = 36,
     VHOST_USER_ADD_MEM_REG = 37,
     VHOST_USER_REM_MEM_REG = 38,
+    VHOST_USER_RESET_VRING = 41,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -1508,6 +1509,45 @@ static int vhost_user_get_max_memslots(struct vhost_dev 
*dev,
     return 0;
 }
 
+static int vhost_user_reset_vring(struct vhost_dev *dev,
+                                  struct vhost_vring_state *ring)
+{
+    int ret;
+    VhostUserMsg msg = {
+        .hdr.request = VHOST_USER_RESET_VRING,
+        .hdr.flags = VHOST_USER_VERSION,
+        .payload.state = *ring,
+        .hdr.size = sizeof(msg.payload.state),
+    };
+
+    if (!virtio_has_feature(dev->acked_features, VIRTIO_F_RING_RESET)) {
+        return -ENOTSUP;
+    }
+
+    ret = vhost_user_write(dev, &msg, NULL, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = vhost_user_read(dev, &msg);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (msg.hdr.request != VHOST_USER_RESET_VRING) {
+        error_report("Received unexpected msg type. Expected %d received %d",
+                     VHOST_USER_RESET_VRING, msg.hdr.request);
+        return -EPROTO;
+    }
+
+    if (msg.hdr.size != sizeof(msg.payload.state)) {
+        error_report("Received bad msg size.");
+        return -EPROTO;
+    }
+
+    return 0;
+}
+
 static int vhost_user_reset_device(struct vhost_dev *dev)
 {
     VhostUserMsg msg = {
@@ -2635,6 +2675,7 @@ const VhostOps user_ops = {
         .vhost_set_features = vhost_user_set_features,
         .vhost_get_features = vhost_user_get_features,
         .vhost_set_owner = vhost_user_set_owner,
+        .vhost_reset_vring = vhost_user_reset_vring,
         .vhost_reset_device = vhost_user_reset_device,
         .vhost_get_vq_index = vhost_user_get_vq_index,
         .vhost_set_vring_enable = vhost_user_set_vring_enable,
diff --git a/include/hw/virtio/vhost-backend.h 
b/include/hw/virtio/vhost-backend.h
index dad7191bac..ec65a55a77 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -79,6 +79,8 @@ typedef int (*vhost_get_features_op)(struct vhost_dev *dev,
                                      uint64_t *features);
 typedef int (*vhost_set_backend_cap_op)(struct vhost_dev *dev);
 typedef int (*vhost_set_owner_op)(struct vhost_dev *dev);
+typedef int (*vhost_reset_vring_op)(struct vhost_dev *dev,
+                                    struct vhost_vring_state *ring);
 typedef int (*vhost_reset_device_op)(struct vhost_dev *dev);
 typedef int (*vhost_get_vq_index_op)(struct vhost_dev *dev, int idx);
 typedef int (*vhost_set_vring_enable_op)(struct vhost_dev *dev,
@@ -156,6 +158,7 @@ typedef struct VhostOps {
     vhost_set_backend_cap_op vhost_set_backend_cap;
     vhost_set_owner_op vhost_set_owner;
     vhost_reset_device_op vhost_reset_device;
+    vhost_reset_vring_op vhost_reset_vring;
     vhost_get_vq_index_op vhost_get_vq_index;
     vhost_set_vring_enable_op vhost_set_vring_enable;
     vhost_set_dev_enable_op vhost_set_dev_enable;
-- 
2.32.0