[RFC PATCH for 8.1 4/6] vdpa: return errno in vhost_vdpa_get_vring_group error

["Eugenio Pérez" <eperezma@redhat.com>]

We need to tell in the caller, as some errors are expected in a normal
workflow.  In particular, parent drivers in recent kernels with
VHOST_BACKEND_F_IOTLB_ASID may not support vring groups.  In that case,
-ENOTSUP is returned.

This is the case of vp_vdpa in Linux 6.2.

Next patches in this series will use that information to know if it must
abort or not.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 net/vhost-vdpa.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 99904a0da7..4397c0d4b3 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -361,6 +361,14 @@ static NetClientInfo net_vhost_vdpa_info = {
         .check_peer_type = vhost_vdpa_check_peer_type,
 };
 
+/**
+ * Get vring virtqueue group
+ *
+ * @device_fd  vdpa device fd
+ * @vq_index   Virtqueue index
+ *
+ * Return -errno in case of error, or vq group if success.
+ */
 static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index)
 {
     struct vhost_vring_state state = {
@@ -369,6 +377,7 @@ static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index)
     int r = ioctl(device_fd, VHOST_VDPA_GET_VRING_GROUP, &state);
 
     if (unlikely(r < 0)) {
+        r = -errno;
         error_report("Cannot get VQ %u group: %s", vq_index,
                      g_strerror(errno));
         return r;
-- 
2.31.1