sock: Introduce the SO_PEEK_OFF sock option

This one specifies where to start MSG_PEEK-ing queue data from. When
set to negative value means that MSG_PEEK works as ususally -- peeks
from the head of the queue always.

When some bytes are peeked from queue and the peeking offset is non
negative it is moved forward so that the next peek will return next
portion of data.

When non-peeking recvmsg occurs and the peeking offset is non negative
is is moved backward so that the next peek will still peek the proper
data (i.e. the one that would have been picked if there were no non
peeking recv in between).

The offset is set using per-proto opteration to let the protocol handle
the locking issues and to check whether the peeking offset feature is
supported by the protocol the socket belongs to.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 0 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 91c1c8baf020..9c0553b9e451 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -357,6 +357,7 @@ struct sock {
         struct page             *sk_sndmsg_page;
         struct sk_buff          *sk_send_head;
         __u32                   sk_sndmsg_off;
+        __s32                   sk_peek_off;
         int                     sk_write_pending;
 #ifdef CONFIG_SECURITY
         void                    *sk_security;
@@ -373,6 +374,30 @@ struct sock {
         void                    (*sk_destruct)(struct sock *sk);
 };
 
+static inline int sk_peek_offset(struct sock *sk, int flags)
+{
+        if ((flags & MSG_PEEK) && (sk->sk_peek_off >= 0))
+                return sk->sk_peek_off;
+        else
+                return 0;
+}
+
+static inline void sk_peek_offset_bwd(struct sock *sk, int val)
+{
+        if (sk->sk_peek_off >= 0) {
+                if (sk->sk_peek_off >= val)
+                        sk->sk_peek_off -= val;
+                else
+                        sk->sk_peek_off = 0;
+        }
+}
+
+static inline void sk_peek_offset_fwd(struct sock *sk, int val)
+{
+        if (sk->sk_peek_off >= 0)
+                sk->sk_peek_off += val;
+}
+
 /*
  * Hashed lists helper routines
  */