net: implement tunnel probing

Tap devices support GSO over UDP tunnel offload. Probe for such
feature in a similar manner to other offloads.

GSO over UDP tunnel needs to be enabled in addition to a "plain"
offload (TSO or USO).

No need to check separately for the outer header checksum offload:
the kernel is going to support both of them or none.

The new features are disabled by default to avoid compat issues,
and could be enabled, after that hw_compat_10_1 will be added,
together with the related compat entries.

Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <a987a8a7613cbf33bb2209c7c7f5889b512638a7.1758549625.git.pabeni@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

net/net.c

@@ -522,6 +522,15 @@ bool qemu_has_uso(NetClientState *nc)
     return nc->info->has_uso(nc);
 }
 
+bool qemu_has_tunnel(NetClientState *nc)
+{
+    if (!nc || !nc->info->has_tunnel) {
+        return false;
+    }
+
+    return nc->info->has_tunnel(nc);
+}
+
 bool qemu_has_vnet_hdr(NetClientState *nc)
 {
     if (!nc || !nc->info->has_vnet_hdr) {

net/tap-bsd.c

@@ -225,6 +225,11 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
+bool tap_probe_has_tunnel(int fd)
+{
+    return false;
+}
+
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }

net/tap-linux.c

@@ -201,6 +201,17 @@ int tap_probe_has_uso(int fd)
     return 1;
 }
 
+bool tap_probe_has_tunnel(int fd)
+{
+    unsigned offload;
+
+    offload = TUN_F_CSUM | TUN_F_TSO4 | TUN_F_UDP_TUNNEL_GSO;
+    if (ioctl(fd, TUNSETOFFLOAD, offload) < 0) {
+        return false;
+    }
+    return true;
+}
+
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
     if (ioctl(fd, TUNSETVNETHDRSZ, &len) == -1) {

net/tap-linux.h

@@ -53,4 +53,13 @@
 #define TUN_F_USO4    0x20    /* I can handle USO for IPv4 packets */
 #define TUN_F_USO6    0x40    /* I can handle USO for IPv6 packets */
 
+/* I can handle TSO/USO for UDP tunneled packets */
+#define TUN_F_UDP_TUNNEL_GSO       0x080
+
+/*
+ * I can handle TSO/USO for UDP tunneled packets requiring csum offload for
+ * the outer header
+ */
+#define TUN_F_UDP_TUNNEL_GSO_CSUM  0x100
+
 #endif /* QEMU_TAP_LINUX_H */

net/tap-solaris.c

@@ -227,6 +227,11 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
+bool tap_probe_has_tunnel(int fd)
+{
+    return false;
+}
+
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }

net/tap-stub.c

@@ -52,6 +52,11 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
+bool tap_probe_has_tunnel(int fd)
+{
+    return false;
+}
+
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }

net/tap.c

@@ -76,6 +76,7 @@ typedef struct TAPState {
     bool using_vnet_hdr;
     bool has_ufo;
     bool has_uso;
+    bool has_tunnel;
     bool enabled;
     VHostNetState *vhost_net;
     unsigned host_vnet_hdr_len;
@@ -246,6 +247,14 @@ static bool tap_has_uso(NetClientState *nc)
     return s->has_uso;
 }
 
+static bool tap_has_tunnel(NetClientState *nc)
+{
+    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+
+    assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
+    return s->has_tunnel;
+}
+
 static bool tap_has_vnet_hdr(NetClientState *nc)
 {
     TAPState *s = DO_UPCAST(TAPState, nc, nc);
@@ -374,6 +383,7 @@ static NetClientInfo net_tap_info = {
     .cleanup = tap_cleanup,
     .has_ufo = tap_has_ufo,
     .has_uso = tap_has_uso,
+    .has_tunnel = tap_has_tunnel,
     .has_vnet_hdr = tap_has_vnet_hdr,
     .has_vnet_hdr_len = tap_has_vnet_hdr_len,
     .set_offload = tap_set_offload,
@@ -403,6 +413,7 @@ static TAPState *net_tap_fd_init(NetClientState *peer,
     s->using_vnet_hdr = false;
     s->has_ufo = tap_probe_has_ufo(s->fd);
     s->has_uso = tap_probe_has_uso(s->fd);
+    s->has_tunnel = tap_probe_has_tunnel(s->fd);
     s->enabled = true;
     tap_set_offload(&s->nc, &ol);
     /*

net/tap_int.h

@@ -38,6 +38,7 @@ void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp);
 int tap_probe_vnet_hdr(int fd, Error **errp);
 int tap_probe_has_ufo(int fd);
 int tap_probe_has_uso(int fd);
+bool tap_probe_has_tunnel(int fd);
 void tap_fd_set_offload(int fd, const NetOffloads *ol);
 void tap_fd_set_vnet_hdr_len(int fd, int len);
 int tap_fd_set_vnet_le(int fd, int vnet_is_le);