[Qemu-devel] [PATCH 2/4] net: add net_is_tap_client()

[Stefan Hajnoczi]

The vhost-net code interacts closely with the net/tap.c backend so that
it can pass the underlying file descriptor to the vhost_net.ko driver.
We need a check that confirms a NetClientState is indeed a tap backend
(and not something else like slirp or socket).

Formalize this in the new net_is_tap_client() function.  This way
callers do not reach inside net internals to check the type.

Note that I've added this function to net/tap.c but named it
net_is_tap_client().  Ideally it should be in net.c but I want to keep
the code where the tap net client is defined.

Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
---
 hw/vhost_net.c  |    5 ++---
 hw/virtio-net.c |    9 +++++----
 net/tap.c       |    5 +++++
 net/tap.h       |    1 +
 4 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/hw/vhost_net.c b/hw/vhost_net.c
index ac3e616..47710ee 100644
--- a/hw/vhost_net.c
+++ b/hw/vhost_net.c
@@ -82,10 +82,9 @@ void vhost_net_ack_features(struct vhost_net *net, unsigned 
features)
 
 static int vhost_net_get_fd(NetClientState *backend)
 {
-    switch (backend->info->type) {
-    case NET_CLIENT_TYPE_TAP:
+    if (net_is_tap_client(backend)) {
         return tap_get_fd(backend);
-    default:
+    } else {
         fprintf(stderr, "vhost-net requires tap backend\n");
         return -EBADFD;
     }
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index d5527d4..1575879 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -108,7 +108,7 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t 
status)
     if (!n->nic->nc.peer) {
         return;
     }
-    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {
+    if (!net_is_tap_client(n->nic->nc.peer)) {
         return;
     }
 
@@ -205,8 +205,9 @@ static int peer_has_vnet_hdr(VirtIONet *n)
     if (!n->nic->nc.peer)
         return 0;
 
-    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP)
+    if (!net_is_tap_client(n->nic->nc.peer)) {
         return 0;
+    }
 
     n->has_vnet_hdr = tap_has_vnet_hdr(n->nic->nc.peer);
 
@@ -249,7 +250,7 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev, 
uint32_t features)
     }
 
     if (!n->nic->nc.peer ||
-        n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {
+        !net_is_tap_client(n->nic->nc.peer)) {
         return features;
     }
     if (!tap_get_vhost_net(n->nic->nc.peer)) {
@@ -288,7 +289,7 @@ static void virtio_net_set_features(VirtIODevice *vdev, 
uint32_t features)
                         (features >> VIRTIO_NET_F_GUEST_UFO)  & 1);
     }
     if (!n->nic->nc.peer ||
-        n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {
+        !net_is_tap_client(n->nic->nc.peer)) {
         return;
     }
     if (!tap_get_vhost_net(n->nic->nc.peer)) {
diff --git a/net/tap.c b/net/tap.c
index 20ce3ff..d5bdfa0 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -303,6 +303,11 @@ static void tap_poll(NetClientState *nc, bool enable)
     tap_write_poll(s, enable);
 }
 
+bool net_is_tap_client(NetClientState *nc)
+{
+    return nc->info->type == NET_CLIENT_TYPE_TAP;
+}
+
 int tap_get_fd(NetClientState *nc)
 {
     TAPState *s = DO_UPCAST(TAPState, nc, nc);
diff --git a/net/tap.h b/net/tap.h
index 2966d81..9a341bf 100644
--- a/net/tap.h
+++ b/net/tap.h
@@ -52,6 +52,7 @@ int tap_probe_has_ufo(int fd);
 void tap_fd_set_offload(int fd, int csum, int tso4, int tso6, int ecn, int 
ufo);
 void tap_fd_set_vnet_hdr_len(int fd, int len);
 
+bool net_is_tap_client(NetClientState *nc);
 int tap_get_fd(NetClientState *nc);
 
 struct vhost_net;
-- 
1.7.10