vdpa: manual forward CVQ buffers

Do a simple forwarding of CVQ buffers, the same work SVQ could do but
through callbacks. No functional change intended.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/vhost-vdpa.c

@@ -11,11 +11,14 @@
 
 #include "qemu/osdep.h"
 #include "clients.h"
+#include "hw/virtio/virtio-net.h"
 #include "net/vhost_net.h"
 #include "net/vhost-vdpa.h"
 #include "hw/virtio/vhost-vdpa.h"
 #include "qemu/config-file.h"
 #include "qemu/error-report.h"
+#include "qemu/log.h"
+#include "qemu/memalign.h"
 #include "qemu/option.h"
 #include "qapi/error.h"
 #include <linux/vhost.h>
@@ -187,6 +190,57 @@ static NetClientInfo net_vhost_vdpa_info = {
         .check_peer_type = vhost_vdpa_check_peer_type,
 };
 
+/**
+ * Forward buffer for the moment.
+ */
+static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
+                                            VirtQueueElement *elem,
+                                            void *opaque)
+{
+    unsigned int n = elem->out_num + elem->in_num;
+    g_autofree struct iovec *dev_buffers = g_new(struct iovec, n);
+    size_t in_len, dev_written;
+    virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
+    int r;
+
+    memcpy(dev_buffers, elem->out_sg, elem->out_num);
+    memcpy(dev_buffers + elem->out_num, elem->in_sg, elem->in_num);
+
+    r = vhost_svq_add(svq, &dev_buffers[0], elem->out_num, &dev_buffers[1],
+                      elem->in_num, elem);
+    if (unlikely(r != 0)) {
+        if (unlikely(r == -ENOSPC)) {
+            qemu_log_mask(LOG_GUEST_ERROR, "%s: No space on device queue\n",
+                          __func__);
+        }
+        goto out;
+    }
+
+    /*
+     * We can poll here since we've had BQL from the time we sent the
+     * descriptor. Also, we need to take the answer before SVQ pulls by itself,
+     * when BQL is released
+     */
+    dev_written = vhost_svq_poll(svq);
+    if (unlikely(dev_written < sizeof(status))) {
+        error_report("Insufficient written data (%zu)", dev_written);
+    }
+
+out:
+    in_len = iov_from_buf(elem->in_sg, elem->in_num, 0, &status,
+                          sizeof(status));
+    if (unlikely(in_len < sizeof(status))) {
+        error_report("Bad device CVQ written length");
+    }
+    vhost_svq_push_elem(svq, elem, MIN(in_len, sizeof(status)));
+    g_free(elem);
+    return r;
+}
+
+static const VhostShadowVirtqueueOps vhost_vdpa_net_svq_ops = {
+    .avail_handler = vhost_vdpa_net_handle_ctrl_avail,
+};
+
 static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
                                            const char *device,
                                            const char *name,
@@ -211,6 +265,10 @@ static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
 
     s->vhost_vdpa.device_fd = vdpa_device_fd;
     s->vhost_vdpa.index = queue_pair_index;
+    if (!is_datapath) {
+        s->vhost_vdpa.shadow_vq_ops = &vhost_vdpa_net_svq_ops;
+        s->vhost_vdpa.shadow_vq_ops_opaque = s;
+    }
     ret = vhost_vdpa_add(nc, (void *)&s->vhost_vdpa, queue_pair_index, nvqs);
     if (ret) {
         qemu_del_net_client(nc);