[PATCH v8 1/2] [PATCH 1/2] Introduce virtio_net_handle_tx_dispatch() to unify TX path handling. This dispatcher dynamically selects between timer-based and BH-based TX processing based on configuration.

[Koushik Dutta <kdutta@redhat.com>]

Previously, the tx=timer selected between two completely separate
code paths at queue creation time. This refactoring introduces a
runtime dispatch mechanism while maintaining identical behavior.

This is a preparatory patch with no functional changes, making it
easier to add dynamic TX notification coalescing in a subsequent patch.

Signed-off-by: Koushik Dutta <kdutta@redhat.com>
---
 hw/net/virtio-net.c            | 44 ++++++++++++++++++++++------------
 include/hw/virtio/virtio-net.h |  1 +
 2 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 2a5d642a64..319842cf28 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1002,6 +1002,8 @@ static void virtio_net_set_features(VirtIODevice *vdev,
     }
 }
 
+static void virtio_net_tx_timer(void *opaque);
+
 static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd,
                                      struct iovec *iov, unsigned int iov_cnt)
 {
@@ -2817,7 +2819,6 @@ detach:
     return -EINVAL;
 }
 
-static void virtio_net_tx_timer(void *opaque);
 
 static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)
 {
@@ -2973,6 +2974,22 @@ static void virtio_net_tx_bh(void *opaque)
     }
 }
 
+static void virtio_net_handle_tx_dispatch(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIONet *n = VIRTIO_NET(vdev);
+    VirtIONetQueue *q = &n->vqs[vq2q(virtio_get_queue_index(vq))];
+
+    if (n->tx_timer_activate) {
+        if (q->tx_timer == NULL) {
+            q->tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
+                                       virtio_net_tx_timer, q);
+        }
+        virtio_net_handle_tx_timer(vdev, vq);
+    } else {
+        virtio_net_handle_tx_bh(vdev, vq);
+    }
+}
+
 static void virtio_net_add_queue(VirtIONet *n, int index)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
@@ -2980,20 +2997,13 @@ static void virtio_net_add_queue(VirtIONet *n, int index)
     n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
                                            virtio_net_handle_rx);
 
-    if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
-        n->vqs[index].tx_vq =
-            virtio_add_queue(vdev, n->net_conf.tx_queue_size,
-                             virtio_net_handle_tx_timer);
-        n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
-                                              virtio_net_tx_timer,
-                                              &n->vqs[index]);
-    } else {
-        n->vqs[index].tx_vq =
-            virtio_add_queue(vdev, n->net_conf.tx_queue_size,
-                             virtio_net_handle_tx_bh);
-        n->vqs[index].tx_bh = qemu_bh_new_guarded(virtio_net_tx_bh, &n->vqs[index],
-                                                  &DEVICE(vdev)->mem_reentrancy_guard);
-    }
+    n->vqs[index].tx_vq =
+        virtio_add_queue(vdev, n->net_conf.tx_queue_size,
+                         virtio_net_handle_tx_dispatch);
+
+    n->vqs[index].tx_bh =
+        qemu_bh_new_guarded(virtio_net_tx_bh, &n->vqs[index],
+                            &DEVICE(vdev)->mem_reentrancy_guard);
 
     n->vqs[index].tx_waiting = 0;
     n->vqs[index].n = n;
@@ -3970,6 +3980,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
         error_printf("Defaulting to \"bh\"");
     }
 
+    if (n->net_conf.tx && strcmp(n->net_conf.tx, "timer") == 0) {
+        n->tx_timer_activate = true;
+    }
+
     n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n),
                                     n->net_conf.tx_queue_size);
 
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 371e376428..a4eb3f407e 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -230,6 +230,7 @@ struct VirtIONet {
     struct EBPFRSSContext ebpf_rss;
     uint32_t nr_ebpf_rss_fds;
     char **ebpf_rss_fds;
+    bool tx_timer_activate;
 };
 
 size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
-- 
2.53.0