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/net/vhost-user.c b/net/vhost-user.c
index 8a3df27b02..bf892915de 100644
--- a/net/vhost-user.c
+++ b/net/vhost-user.c
@@ -138,6 +138,7 @@ static int vhost_user_start(int queues, NetClientState *ncs[],
         options.busyloop_timeout = 0;
         options.nvqs = 2;
         options.feature_bits = user_feature_bits;
+        options.max_tx_queue_size = VIRTQUEUE_MAX_SIZE;
         options.get_acked_features = vhost_user_get_acked_features;
         options.save_acked_features = vhost_user_save_acked_features;