vtnet: move offload functions to virtio_net.h to share them

Move the functions vtnet_rxq_csum() and vtnet_txq_offload() and the
subfunctions they call from if_vtnet.c to virtio_net.h. This allows
us to call these functions from if_tuntap.c and if_ptnet.c.
virtio_net.h already contained a copy of these functions, but a copy
of an outdated version. The functions evolved in if_vtnet.c.
In if_vtnet.c, the copy has never been used because it increments
counters in their own functions.
This patch removes the outdated copy from virtio_net.h and moves the
new version of the functions from if_vtnet.c to virtio_net.h.
if_tuntap.c, if_ptnet.c, and if_vtnet.c just call these functions,
and if_vtnet.c increments its counters depending on the return value.

Reviewed by:		tuexen
MFC after:		1 month
MFC to:			stable/15
Differential Revision:	https://reviews.freebsd.org/D57299

1 files changed, 19 insertions, 3 deletions

diff --git a/sys/dev/netmap/if_ptnet.c b/sys/dev/netmap/if_ptnet.c
index 9c06f7fec530..660b1930aa76 100644
--- a/sys/dev/netmap/if_ptnet.c
+++ b/sys/dev/netmap/if_ptnet.c
@@ -1464,8 +1464,17 @@ ptnet_drain_transmit_queue(struct ptnet_queue *pq, unsigned int budget,
 			 * two 8-bytes-wide writes. */
 			memset(nmbuf, 0, PTNET_HDR_SIZE);
 			if (mhead->m_pkthdr.csum_flags & PTNET_ALL_OFFLOAD) {
-				mhead = virtio_net_tx_offload(ifp, mhead, false,
-							 vh);
+				/*
+				 * Translate the CSUM_* flags in the mbuf to the
+				 * corresponding flags in the VirtIO header.
+				 *
+				 * ptnet does not negotiate ECN and orders the
+				 * bytes in the VirtIO header as if the VirtIO
+				 * modern mode is not used. So, pass false for
+				 * both.
+				 */
+				virtio_net_tx_offload(ifp, &mhead, vh, false,
+				    false);
 				if (unlikely(!mhead)) {
 					/* Packet dropped because errors
 					 * occurred while preparing the vnet
@@ -1842,7 +1851,14 @@ host_sync:
 			}
 		}
 
-		if (unlikely(have_vnet_hdr && virtio_net_rx_csum(mhead, vh))) {
+		/*
+		 * Translate the VirtIO header flags to the corresponding
+		 * CSUM_* flags in the mbuf.
+		 */
+		if (unlikely(have_vnet_hdr &&
+		    ((vh->flags & (VIRTIO_NET_HDR_F_NEEDS_CSUM |
+		      VIRTIO_NET_HDR_F_DATA_VALID)) != 0) &&
+		    (virtio_net_rx_csum(mhead, vh) != 0))) {
 			m_freem(mhead);
 			nm_prlim(1, "Csum offload error: dropping");
 			pq->stats.iqdrops ++;