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 c7d39e3263
("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 351782067b ("ipv4: ipcm_cookie initializers").
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
c6af0c227a