vu_common: Always set num_buffers in virtio-net header

Legacy virtio used two different header formats: struct virtio_net_hdr
(10 bytes) when VIRTIO_NET_F_MRG_RXBUF was not negotiated, and
struct virtio_net_hdr_mrg_rxbuf (12 bytes) when it was.  The
num_buffers field only existed in the larger header.

Modern virtio (VIRTIO_F_VERSION_1, i.e. virtio 1.0+) always uses the
12-byte struct virtio_net_hdr_mrg_rxbuf header regardless of whether
VIRTIO_NET_F_MRG_RXBUF is negotiated, so num_buffers is always present
in the header.  passt only supports modern virtio and dies if
VIRTIO_F_VERSION_1 is not negotiated (vhost_user.c), and VNET_HLEN is
unconditionally defined as sizeof(struct virtio_net_hdr_mrg_rxbuf).

The virtio specification (v1.1, section 5.1.6) requires that:

  "The device MUST set num_buffers to 1 if VIRTIO_NET_F_MRG_RXBUF has
   not been negotiated."

vu_set_vnethdr() only set num_buffers when VIRTIO_NET_F_MRG_RXBUF was
negotiated.  When it was not, num_buffers was left uninitialised,
violating the spec.

Since vu_collect() already limits buffer collection to a single element
when VIRTIO_NET_F_MRG_RXBUF is not negotiated, num_buffers passed by
callers is guaranteed to be 1 in that case.  We can therefore
unconditionally set num_buffers, which makes the vdev parameter
unnecessary.

Drop the vdev parameter from vu_set_vnethdr() and update all callers.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

0 files changed, 0 insertions, 0 deletions