packet: add PACKET_RESERVE sockopt

Add new sockopt to reserve some headroom in the mmaped ring frames in
front of the packet payload. This can be used f.i. when the VLAN header
needs to be (re)constructed to avoid moving the entire payload.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
index a630295..18db066 100644 (file)
--- a/include/linux/if_packet.h
+++ b/include/linux/if_packet.h
@@ -45,6 +45,7 @@ struct sockaddr_ll
 #define PACKET_ORIGDEV                 9
 #define PACKET_VERSION                 10
 #define PACKET_HDRLEN                  11
+#define PACKET_RESERVE                 12
 
 struct tpacket_stats
 {

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index db792e0..de73bcb 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -188,6 +188,7 @@ struct packet_sock {
        unsigned int            pg_vec_len;
        enum tpacket_versions   tp_version;
        unsigned int            tp_hdrlen;
+       unsigned int            tp_reserve;
 #endif
 };
 
@@ -635,11 +636,13 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
                snaplen = res;
 
        if (sk->sk_type == SOCK_DGRAM) {
-               macoff = netoff = TPACKET_ALIGN(po->tp_hdrlen) + 16;
+               macoff = netoff = TPACKET_ALIGN(po->tp_hdrlen) + 16 +
+                                 po->tp_reserve;
        } else {
                unsigned maclen = skb_network_offset(skb);
                netoff = TPACKET_ALIGN(po->tp_hdrlen +
-                                      (maclen < 16 ? 16 : maclen));
+                                      (maclen < 16 ? 16 : maclen)) +
+                       po->tp_reserve;
                macoff = netoff - maclen;
        }
 
@@ -1448,6 +1451,19 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
                        return -EINVAL;
                }
        }
+       case PACKET_RESERVE:
+       {
+               unsigned int val;
+
+               if (optlen != sizeof(val))
+                       return -EINVAL;
+               if (po->pg_vec)
+                       return -EBUSY;
+               if (copy_from_user(&val, optval, sizeof(val)))
+                       return -EFAULT;
+               po->tp_reserve = val;
+               return 0;
+       }
 #endif
        case PACKET_AUXDATA:
        {
@@ -1547,6 +1563,12 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
                }
                data = &val;
                break;
+       case PACKET_RESERVE:
+               if (len > sizeof(unsigned int))
+                       len = sizeof(unsigned int);
+               val = po->tp_reserve;
+               data = &val;
+               break;
 #endif
        default:
                return -ENOPROTOOPT;
@@ -1790,7 +1812,8 @@ static int packet_set_ring(struct sock *sk, struct tpacket_req *req, int closing
                        return -EINVAL;
                if (unlikely(req->tp_block_size & (PAGE_SIZE - 1)))
                        return -EINVAL;
-               if (unlikely(req->tp_frame_size < po->tp_hdrlen))
+               if (unlikely(req->tp_frame_size < po->tp_hdrlen +
+                                                 po->tp_reserve))
                        return -EINVAL;
                if (unlikely(req->tp_frame_size & (TPACKET_ALIGNMENT - 1)))
                        return -EINVAL;