No need to check the support of mergeable buffer inside the recevie
loop as the whole handle_rx()_xx is in the read critical region.  So
this patch move it ahead of the receiving loop.

Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 drivers/vhost/net.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 14fc189..95e49de 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -411,7 +411,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
        };
 
        size_t total_len = 0;
-       int err, headcount;
+       int err, headcount, mergeable;
        size_t vhost_hlen, sock_hlen;
        size_t vhost_len, sock_len;
        struct socket *sock = rcu_dereference(vq->private_data);
@@ -425,6 +425,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
 
        vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
                vq->log : NULL;
+       mergeable = vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF);
 
        while ((sock_len = peek_head_len(sock->sk))) {
                sock_len += sock_hlen;
@@ -474,7 +475,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
                        break;
                }
                /* TODO: Should check and handle checksum. */
-               if (vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF) &&
+               if (likely(mergeable) &&
                    memcpy_toiovecend(vq->hdr, (unsigned char *)&headcount,
                                      offsetof(typeof(hdr), num_buffers),
                                      sizeof hdr.num_buffers)) {

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