virtio: Don't expose legacy net features when VIRTIO_NET_NO_LEGACY defined.

In particular, the virtio header always has the u16 num_buffers field.
We define a new 'struct virtio_net_hdr_v1' for this (rather than
simply calling it 'struct virtio_net_hdr', to avoid nasty type errors
if some parts of a project define VIRTIO_NET_NO_LEGACY and some don't.

Transitional devices (which can't define VIRTIO_NET_NO_LEGACY) will
have to keep using struct virtio_net_hdr_mrg_rxbuf, which has the same
byte layout as struct virtio_net_hdr_v1.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 30 insertions, 2 deletions

diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index b5f1677b291c..4a9b58113d6e 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -35,7 +35,6 @@
 #define VIRTIO_NET_F_CSUM       0       /* Host handles pkts w/ partial csum */
 #define VIRTIO_NET_F_GUEST_CSUM 1       /* Guest handles pkts w/ partial csum */
 #define VIRTIO_NET_F_MAC        5       /* Host has given MAC address. */
-#define VIRTIO_NET_F_GSO        6       /* Host handles pkts w/ any GSO type */
 #define VIRTIO_NET_F_GUEST_TSO4 7       /* Guest can handle TSOv4 in. */
 #define VIRTIO_NET_F_GUEST_TSO6 8       /* Guest can handle TSOv6 in. */
 #define VIRTIO_NET_F_GUEST_ECN  9       /* Guest can handle TSO[6] w/ ECN in. */
@@ -56,6 +55,10 @@
                                          * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23   /* Set MAC address */
 
+#ifndef VIRTIO_NET_NO_LEGACY
+#define VIRTIO_NET_F_GSO        6       /* Host handles pkts w/ any GSO type */
+#endif /* VIRTIO_NET_NO_LEGACY */
+
 #define VIRTIO_NET_S_LINK_UP    1       /* Link is up */
 #define VIRTIO_NET_S_ANNOUNCE   2       /* Announcement is needed */
 
@@ -71,8 +74,9 @@ struct virtio_net_config {
         __u16 max_virtqueue_pairs;
 } __attribute__((packed));
 
+#ifndef VIRTIO_NET_NO_LEGACY
 /* This header comes first in the scatter-gather list.
- * If VIRTIO_F_ANY_LAYOUT is not negotiated, it must
+ * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must
  * be the first element of the scatter-gather list.  If you don't
  * specify GSO or CSUM features, you can simply ignore the header. */
 struct virtio_net_hdr {
@@ -97,6 +101,30 @@ struct virtio_net_hdr_mrg_rxbuf {
         struct virtio_net_hdr hdr;
         __virtio16 num_buffers; /* Number of merged rx buffers */
 };
+#else /* ... VIRTIO_NET_NO_LEGACY */
+/*
+ * This header comes first in the scatter-gather list.  If you don't
+ * specify GSO or CSUM features, you can simply ignore the header.
+ *
+ * This is bitwise-equivalent to the legacy struct virtio_net_hdr_mrg_rxbuf.
+ */
+struct virtio_net_hdr_v1 {
+#define VIRTIO_NET_HDR_F_NEEDS_CSUM     1       /* Use csum_start, csum_offset */
+#define VIRTIO_NET_HDR_F_DATA_VALID     2       /* Csum is valid */
+        __u8 flags;
+#define VIRTIO_NET_HDR_GSO_NONE         0       /* Not a GSO frame */
+#define VIRTIO_NET_HDR_GSO_TCPV4        1       /* GSO frame, IPv4 TCP (TSO) */
+#define VIRTIO_NET_HDR_GSO_UDP          3       /* GSO frame, IPv4 UDP (UFO) */
+#define VIRTIO_NET_HDR_GSO_TCPV6        4       /* GSO frame, IPv6 TCP */
+#define VIRTIO_NET_HDR_GSO_ECN          0x80    /* TCP has ECN set */
+        __u8 gso_type;
+        __virtio16 hdr_len;     /* Ethernet + IP + tcp/udp hdrs */
+        __virtio16 gso_size;    /* Bytes to append to hdr_len per frame */
+        __virtio16 csum_start;  /* Position to start checksumming from */
+        __virtio16 csum_offset; /* Offset after that to place checksum */
+        __virtio16 num_buffers; /* Number of merged rx buffers */
+};
+#endif /* ...VIRTIO_NET_NO_LEGACY */
 
 /*
  * Control virtqueue data structures