[RFC PATCH v2 1/3] vdpa: Add SetSteeringEBPF method for NetClientState

[Hawkins Jiawei <yin31149@gmail.com>]

At present, to enable the VIRTIO_NET_F_RSS feature, eBPF must
be loaded for the vhost backend.

Given that vhost-vdpa is one of the vhost backend, we need to
implement the SetSteeringEBPF method to support RSS for vhost-vdpa,
even if vhost-vdpa calculates the rss hash in the hardware device
instead of in the kernel by eBPF.

Although this requires QEMU to be compiled with `--enable-bpf`
configuration even if the vdpa device does not use eBPF to
calculate the rss hash, this can avoid adding the specific
conditional statements for vDPA case to enable the VIRTIO_NET_F_RSS
feature, which reduces code maintainbility.

Suggested-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
 net/vhost-vdpa.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index a13b267250..4c8e4b19f6 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -238,6 +238,12 @@ static void vhost_vdpa_cleanup(NetClientState *nc)
     }
 }
 
+/** Dummy SetSteeringEBPF to support RSS for vhost-vdpa backend  */
+static bool vhost_vdpa_set_steering_ebpf(NetClientState *nc, int prog_fd)
+{
+    return true;
+}
+
 static bool vhost_vdpa_has_vnet_hdr(NetClientState *nc)
 {
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
@@ -400,6 +406,7 @@ static NetClientInfo net_vhost_vdpa_info = {
         .has_vnet_hdr = vhost_vdpa_has_vnet_hdr,
         .has_ufo = vhost_vdpa_has_ufo,
         .check_peer_type = vhost_vdpa_check_peer_type,
+        .set_steering_ebpf = vhost_vdpa_set_steering_ebpf,
 };
 
 static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index,
@@ -1215,6 +1222,7 @@ static NetClientInfo net_vhost_vdpa_cvq_info = {
     .has_vnet_hdr = vhost_vdpa_has_vnet_hdr,
     .has_ufo = vhost_vdpa_has_ufo,
     .check_peer_type = vhost_vdpa_check_peer_type,
+    .set_steering_ebpf = vhost_vdpa_set_steering_ebpf,
 };
 
 /*
-- 
2.25.1