datagram: Add offset argument to __skb_recv_datagram

This one is only considered for MSG_PEEK flag and the value pointed by
it specifies where to start peeking bytes from. If the offset happens to
point into the middle of the returned skb, the offset within this skb is
put back to this very argument.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 8 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 6f54d0a17f8e..d3cf12f62c8f 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -132,6 +132,8 @@ out_noerr:
  *      __skb_recv_datagram - Receive a datagram skbuff
  *      @sk: socket
  *      @flags: MSG_ flags
+ *      @off: an offset in bytes to peek skb from. Returns an offset
+ *            within an skb where data actually starts
  *      @peeked: returns non-zero if this packet has been seen before
  *      @err: error code returned
  *
@@ -158,7 +160,7 @@ out_noerr:
  *      the standard around please.
  */
 struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
-                                    int *peeked, int *err)
+                                    int *peeked, int *off, int *err)
 {
         struct sk_buff *skb;
         long timeo;
@@ -183,19 +185,22 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
                 struct sk_buff_head *queue = &sk->sk_receive_queue;
 
                 spin_lock_irqsave(&queue->lock, cpu_flags);
-                skb = skb_peek(queue);
-                if (skb) {
+                skb_queue_walk(queue, skb) {
                         *peeked = skb->peeked;
                         if (flags & MSG_PEEK) {
+                                if (*off >= skb->len) {
+                                        *off -= skb->len;
+                                        continue;
+                                }
                                 skb->peeked = 1;
                                 atomic_inc(&skb->users);
                         } else
                                 __skb_unlink(skb, queue);
-                }
-                spin_unlock_irqrestore(&queue->lock, cpu_flags);
 
-                if (skb)
+                        spin_unlock_irqrestore(&queue->lock, cpu_flags);
                         return skb;
+                }
+                spin_unlock_irqrestore(&queue->lock, cpu_flags);
 
                 /* User doesn't want to wait */
                 error = -EAGAIN;
@@ -215,10 +220,10 @@ EXPORT_SYMBOL(__skb_recv_datagram);
 struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags,
                                   int noblock, int *err)
 {
-        int peeked;
+        int peeked, off = 0;
 
         return __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
-                                   &peeked, err);
+                                   &peeked, &off, err);
 }
 EXPORT_SYMBOL(skb_recv_datagram);