mptcp: add MSG_PEEK support

This patch adds support for MSG_PEEK flag. Packets are not removed
from the receive_queue if MSG_PEEK set in recv() system call.

Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Yonglong Li <liyonglong@chinatelecom.cn>

net/mptcp/protocol.c

@@ -1753,10 +1753,10 @@ static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
  struct msghdr *msg,
  size_t len, int flags)
 {
- struct sk_buff *skb;
+ struct sk_buff *skb, *tmp;
  int copied = 0;
 
- while ((skb = skb_peek(&msk->receive_queue)) != NULL) {
+ skb_queue_walk_safe(&msk->receive_queue, skb, tmp) {
  u32 offset = MPTCP_SKB_CB(skb)->offset;
  u32 data_len = skb->len - offset;
  u32 count = min_t(size_t, len - copied, data_len);
@@ -1774,15 +1774,18 @@ static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
  copied += count;
 
  if (count < data_len) {
- MPTCP_SKB_CB(skb)->offset += count;
+ if (!(flags & MSG_PEEK))
+ MPTCP_SKB_CB(skb)->offset += count;
  break;
  }
 
- /* we will bulk release the skb memory later */
- skb->destructor = NULL;
- msk->rmem_released += skb->truesize;
- __skb_unlink(skb, &msk->receive_queue);
- __kfree_skb(skb);
+ if (!(flags & MSG_PEEK)) {
+ /* we will bulk release the skb memory later */
+ skb->destructor = NULL;
+ msk->rmem_released += skb->truesize;
+ __skb_unlink(skb, &msk->receive_queue);
+ __kfree_skb(skb);
+ }
 
  if (copied >= len)
  break;
@@ -2061,7 +2064,8 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
  pr_debug("msk=%p data_ready=%d rx queue empty=%d copied=%d",
  msk, test_bit(MPTCP_DATA_READY, &msk->flags),
  skb_queue_empty_lockless(&sk->sk_receive_queue), copied);
- mptcp_rcv_space_adjust(msk, copied);
+ if (!(flags & MSG_PEEK))
+ mptcp_rcv_space_adjust(msk, copied);
 
  release_sock(sk);
  return copied;