vhost: cleanup iterator update logic

Recent iterator-related changes in vhost made it
harder to follow the logic fixing up the header.
In fact, the fixup always happens at the same
offset: sizeof(virtio_net_hdr): sometimes the
fixup iterator is updated by copy_to_iter,
sometimes-by iov_iter_advance.

Rearrange code to make this obvious.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 10 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index afa06d28725d..ca7043459e2c 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -591,11 +591,6 @@ static void handle_rx(struct vhost_net *net)
                          * TODO: support TSO.
                          */
                         iov_iter_advance(&msg.msg_iter, vhost_hlen);
-                } else {
-                        /* It'll come from socket; we'll need to patch
-                         * ->num_buffers over if VIRTIO_NET_F_MRG_RXBUF
-                         */
-                        iov_iter_advance(&fixup, sizeof(hdr));
                 }
                 err = sock->ops->recvmsg(NULL, sock, &msg,
                                          sock_len, MSG_DONTWAIT | MSG_TRUNC);
@@ -609,11 +604,18 @@ static void handle_rx(struct vhost_net *net)
                         continue;
                 }
                 /* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
-                if (unlikely(vhost_hlen) &&
-                    copy_to_iter(&hdr, sizeof(hdr), &fixup) != sizeof(hdr)) {
-                        vq_err(vq, "Unable to write vnet_hdr at addr %p\n",
-                               vq->iov->iov_base);
-                        break;
+                if (unlikely(vhost_hlen)) {
+                        if (copy_to_iter(&hdr, sizeof(hdr),
+                                         &fixup) != sizeof(hdr)) {
+                                vq_err(vq, "Unable to write vnet_hdr "
+                                       "at addr %p\n", vq->iov->iov_base);
+                                break;
+                        }
+                } else {
+                        /* Header came from socket; we'll need to patch
+                         * ->num_buffers over if VIRTIO_NET_F_MRG_RXBUF
+                         */
+                        iov_iter_advance(&fixup, sizeof(hdr));
                 }
                 /* TODO: Should check and handle checksum. */