[PATCH v4 6/8] vdpa: Move vhost_svq_poll() to the caller of vhost_vdpa_net_cvq_add()

[Hawkins Jiawei <yin31149@gmail.com>]

This patch moves vhost_svq_poll() to the caller of
vhost_vdpa_net_cvq_add() and introduces a helper funtion.

By making this change, next patches in this series is
able to refactor vhost_vdpa_net_load_x() only to delay
the polling and checking process until either the SVQ
is full or control commands shadow buffers are full.

Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v4:
  - always check the return value of vhost_vdpa_net_svq_poll()
suggested Eugenio

v3: https://lore.kernel.org/all/152177c4e7082236fba9d31d535e40f8c2984349.1689748694.git.yin31149@gmail.com/

 net/vhost-vdpa.c | 53 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 43 insertions(+), 10 deletions(-)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 116a06cc45..d9b8b3cf6c 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -609,15 +609,21 @@ static ssize_t vhost_vdpa_net_cvq_add(VhostVDPAState *s,
             qemu_log_mask(LOG_GUEST_ERROR, "%s: No space on device queue\n",
                           __func__);
         }
-        return r;
     }
 
-    /*
-     * 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
-     */
-    return vhost_svq_poll(svq, 1);
+    return r;
+}
+
+/*
+ * Convenience wrapper to poll SVQ for multiple control commands.
+ *
+ * Caller should hold the BQL when invoking this function, and should take
+ * the answer before SVQ pulls by itself when BQL is released.
+ */
+static ssize_t vhost_vdpa_net_svq_poll(VhostVDPAState *s, size_t cmds_in_flight)
+{
+    VhostShadowVirtqueue *svq = g_ptr_array_index(s->vhost_vdpa.shadow_vqs, 0);
+    return vhost_svq_poll(svq, cmds_in_flight);
 }
 
 /* Convenience wrapper to get number of available SVQ descriptors */
@@ -645,6 +651,7 @@ static ssize_t vhost_vdpa_net_load_cmd(VhostVDPAState *s, uint8_t class,
         .iov_base = s->status,
         .iov_len = sizeof(*s->status),
     };
+    ssize_t r;
 
     assert(data_size < vhost_vdpa_net_cvq_cmd_page_len() - sizeof(ctrl));
     /* Each CVQ command has one out descriptor and one in descriptor */
@@ -657,7 +664,16 @@ static ssize_t vhost_vdpa_net_load_cmd(VhostVDPAState *s, uint8_t class,
     iov_to_buf(data_sg, data_num, 0,
                s->cvq_cmd_out_buffer + sizeof(ctrl), data_size);
 
-    return vhost_vdpa_net_cvq_add(s, &out, 1, &in, 1);
+    r = vhost_vdpa_net_cvq_add(s, &out, 1, &in, 1);
+    if (unlikely(r < 0)) {
+        return r;
+    }
+
+    /*
+     * We can poll here since we've had BQL from the time
+     * we sent the descriptor.
+     */
+    return vhost_vdpa_net_svq_poll(s, 1);
 }
 
 static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n)
@@ -1150,6 +1166,15 @@ static int vhost_vdpa_net_excessive_mac_filter_cvq_add(VhostVDPAState *s,
     if (unlikely(r < 0)) {
         return r;
     }
+
+    /*
+     * We can poll here since we've had BQL from the time
+     * we sent the descriptor.
+     */
+    r = vhost_vdpa_net_svq_poll(s, 1);
+    if (unlikely(r < sizeof(*s->status))) {
+        return r;
+    }
     if (*s->status != VIRTIO_NET_OK) {
         return sizeof(*s->status);
     }
@@ -1269,10 +1294,18 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
             goto out;
         }
     } else {
-        dev_written = vhost_vdpa_net_cvq_add(s, &out, 1, &vdpa_in, 1);
-        if (unlikely(dev_written < 0)) {
+        ssize_t r;
+        r = vhost_vdpa_net_cvq_add(s, &out, 1, &vdpa_in, 1);
+        if (unlikely(r < 0)) {
+            dev_written = r;
             goto out;
         }
+
+        /*
+         * We can poll here since we've had BQL from the time
+         * we sent the descriptor.
+         */
+        dev_written = vhost_vdpa_net_svq_poll(s, 1);
     }
 
     if (unlikely(dev_written < sizeof(status))) {
-- 
2.25.1