net: Allow network backends to advertise max TX queue size

This commit refactors how the maximum transmit queue size for
virtio-net devices is determined, making the mechanism more generic
and extensible.

Previously, virtio_net_max_tx_queue_size() contained hardcoded
checks for specific network backend types (vhost-user and
vhost-vdpa) to determine their supported maximum queue size. This
created direct dependencies and would require modifications for
every new backend that supports variable queue sizes.

To improve flexibility, a new max_tx_queue_size field is added
to the vhost_net structure. This allows each network backend
to advertise its supported maximum transmit queue size directly.

The virtio_net_max_tx_queue_size() function now retrieves the max
TX queue size from the vhost_net struct, if available and set.
Otherwise, it defaults to VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 976d2b315a..74d2e3ed90 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -245,6 +245,7 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
     net->dev.nvqs = options->nvqs;
     net->feature_bits = options->feature_bits;
     net->save_acked_features = options->save_acked_features;
+    net->max_tx_queue_size = options->max_tx_queue_size;
 
     net->dev.max_queues = 1;
     net->dev.vqs = net->vqs;