Enable setting skb->mark for UDP and RAW sockets using cmsg.
This is analogous to existing support for TOS, TTL, txtime, etc.
Packet sockets already support this as of commit 
c7d39e32632e
("packet: support per-packet fwmark for af_packet sendmsg").
Similar to other fields, implement by
1. initialize the sockcm_cookie.mark from socket option sk_mark
2. optionally overwrite this in ip_cmsg_send/ip6_datagram_send_ctl
3. initialize inet_cork.mark from sockcm_cookie.mark
4. initialize each (usually just one) skb->mark from inet_cork.mark
Step 1 is handled in one location for most protocols by ipcm_init_sk
as of commit 
351782067b6b ("ipv4: ipcm_cookie initializers").
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
        char                    priority;
        __u16                   gso_size;
        u64                     transmit_time;
+       u32                     mark;
 };
 
 struct inet_cork_full {
 
 {
        ipcm_init(ipcm);
 
+       ipcm->sockc.mark = inet->sk.sk_mark;
        ipcm->sockc.tsflags = inet->sk.sk_tsflags;
        ipcm->oif = inet->sk.sk_bound_dev_if;
        ipcm->addr = inet->inet_saddr;
 
        cork->length = 0;
        cork->ttl = ipc->ttl;
        cork->tos = ipc->tos;
+       cork->mark = ipc->sockc.mark;
        cork->priority = ipc->priority;
        cork->transmit_time = ipc->sockc.transmit_time;
        cork->tx_flags = 0;
        }
 
        skb->priority = (cork->tos != -1) ? cork->priority: sk->sk_priority;
-       skb->mark = sk->sk_mark;
+       skb->mark = cork->mark;
        skb->tstamp = cork->transmit_time;
        /*
         * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
 
        } else if (!ipc.oif)
                ipc.oif = inet->uc_index;
 
-       flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
+       flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos,
                           RT_SCOPE_UNIVERSE, sk->sk_protocol,
                           inet_sk_flowi_flags(sk), faddr, saddr, 0, 0,
                           sk->sk_uid);
 
        skb_reserve(skb, hlen);
 
        skb->priority = sk->sk_priority;
-       skb->mark = sk->sk_mark;
+       skb->mark = sockc->mark;
        skb->tstamp = sockc->transmit_time;
        skb_dst_set(skb, &rt->dst);
        *rtp = NULL;
                }
        }
 
-       flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
+       flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos,
                           RT_SCOPE_UNIVERSE,
                           hdrincl ? IPPROTO_RAW : sk->sk_protocol,
                           inet_sk_flowi_flags(sk) |
 
 
                fl4 = &fl4_stack;
 
-               flowi4_init_output(fl4, ipc.oif, sk->sk_mark, tos,
+               flowi4_init_output(fl4, ipc.oif, ipc.sockc.mark, tos,
                                   RT_SCOPE_UNIVERSE, sk->sk_protocol,
                                   flow_flags,
                                   faddr, saddr, dport, inet->inet_sport,
 
        cork->base.fragsize = mtu;
        cork->base.gso_size = ipc6->gso_size;
        cork->base.tx_flags = 0;
+       cork->base.mark = ipc6->sockc.mark;
        sock_tx_timestamp(sk, ipc6->sockc.tsflags, &cork->base.tx_flags);
 
        if (dst_allfrag(xfrm_dst_path(&rt->dst)))
        hdr->daddr = *final_dst;
 
        skb->priority = sk->sk_priority;
-       skb->mark = sk->sk_mark;
+       skb->mark = cork->base.mark;
 
        skb->tstamp = cork->base.transmit_time;
 
 
 
        skb->protocol = htons(ETH_P_IPV6);
        skb->priority = sk->sk_priority;
-       skb->mark = sk->sk_mark;
+       skb->mark = sockc->mark;
        skb->tstamp = sockc->transmit_time;
 
        skb_put(skb, length);
 
        ipcm6_init(&ipc6);
        ipc6.sockc.tsflags = sk->sk_tsflags;
+       ipc6.sockc.mark = sk->sk_mark;
 
        if (sin6) {
                if (addr_len < SIN6_LEN_RFC2133)
        opt = ipv6_fixup_options(&opt_space, opt);
 
        fl6.flowi6_proto = proto;
+       fl6.flowi6_mark = ipc6.sockc.mark;
 
        if (!hdrincl) {
                rfv.msg = msg;
 
        ipcm6_init(&ipc6);
        ipc6.gso_size = up->gso_size;
        ipc6.sockc.tsflags = sk->sk_tsflags;
+       ipc6.sockc.mark = sk->sk_mark;
 
        /* destination address check */
        if (sin6) {
        if (!fl6.flowi6_oif)
                fl6.flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
 
-       fl6.flowi6_mark = sk->sk_mark;
+       fl6.flowi6_mark = ipc6.sockc.mark;
        fl6.flowi6_uid = sk->sk_uid;
 
        if (msg->msg_controllen) {