net: add tap_set_offload()

This API allows virtio-net to enable various offload features on a
tap interface - e.g. to tell the host kernel it can pass up partial
checksums to userspace.
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

net.c

@@ -1302,6 +1302,9 @@ int tap_has_vnet_hdr(VLANClientState *vc)
 void tap_using_vnet_hdr(VLANClientState *vc, int using_vnet_hdr)
 {
 }
+void tap_set_offload(VLANClientState *vc, int csum, int tso4, int tso6, int ecn)
+{
+}
 #else /* !defined(_WIN32) */
 
 /* Maximum GSO packet size (64k) plus plenty of room for
@@ -1539,6 +1542,27 @@ static int tap_probe_vnet_hdr(int fd)
     return ifr.ifr_flags & IFF_VNET_HDR;
 }
 
+void tap_set_offload(VLANClientState *vc, int csum, int tso4, int tso6, int ecn)
+{
+    TAPState *s = vc->opaque;
+    unsigned int offload = 0;
+
+    if (csum) {
+        offload |= TUN_F_CSUM;
+        if (tso4)
+            offload |= TUN_F_TSO4;
+        if (tso6)
+            offload |= TUN_F_TSO6;
+        if ((tso4 || tso6) && ecn)
+            offload |= TUN_F_TSO_ECN;
+    }
+
+    if (ioctl(s->fd, TUNSETOFFLOAD, offload) != 0) {
+        fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
+                strerror(errno));
+    }
+}
+
 static void tap_cleanup(VLANClientState *vc)
 {
     TAPState *s = vc->opaque;

net.h

@@ -182,5 +182,6 @@ void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
 
 int tap_has_vnet_hdr(VLANClientState *vc);
 void tap_using_vnet_hdr(VLANClientState *vc, int using_vnet_hdr);
+void tap_set_offload(VLANClientState *vc, int csum, int tso4, int tso6, int ecn);
 
 #endif

tap-linux.h

@@ -22,6 +22,7 @@
 /* Ioctl defines */
 #define TUNSETIFF     _IOW('T', 202, int)
 #define TUNGETFEATURES _IOR('T', 207, unsigned int)
+#define TUNSETOFFLOAD  _IOW('T', 208, unsigned int)
 #define TUNGETIFF      _IOR('T', 210, unsigned int)
 #define TUNSETSNDBUF   _IOW('T', 212, int)
 
@@ -30,6 +31,12 @@
 #define IFF_NO_PI	0x1000
 #define IFF_VNET_HDR	0x4000
 
+/* Features for GSO (TUNSETOFFLOAD). */
+#define TUN_F_CSUM	0x01	/* You can hand me unchecksummed packets. */
+#define TUN_F_TSO4	0x02	/* I can handle TSO for IPv4 packets */
+#define TUN_F_TSO6	0x04	/* I can handle TSO for IPv6 packets */
+#define TUN_F_TSO_ECN	0x08	/* I can handle TSO with ECN bits. */
+
 struct virtio_net_hdr
 {
     uint8_t flags;