sctp: implement SIOCINQ ioctl() (take 3)

This simple patch copies the current approach for SIOCINQ ioctl() from DCCP
into SCTP so that the userland code working with SCTP can use a similar
interface across different protocols to know how much space to allocate for
a buffer.

Signed-off-by: Diego Elio Pettenò <flameeyes@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index cf6dcc9..6a691d8 100644 (file)
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3592,7 +3592,40 @@ out:
 /* The SCTP ioctl handler. */
 SCTP_STATIC int sctp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 {
-       return -ENOIOCTLCMD;
+       int rc = -ENOTCONN;
+
+       sctp_lock_sock(sk);
+
+       /*
+        * SEQPACKET-style sockets in LISTENING state are valid, for
+        * SCTP, so only discard TCP-style sockets in LISTENING state.
+        */
+       if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING))
+               goto out;
+
+       switch (cmd) {
+       case SIOCINQ: {
+               struct sk_buff *skb;
+               unsigned int amount = 0;
+
+               skb = skb_peek(&sk->sk_receive_queue);
+               if (skb != NULL) {
+                       /*
+                        * We will only return the amount of this packet since
+                        * that is all that will be read.
+                        */
+                       amount = skb->len;
+               }
+               rc = put_user(amount, (int __user *)arg);
+       }
+               break;
+       default:
+               rc = -ENOIOCTLCMD;
+               break;
+       }
+out:
+       sctp_release_sock(sk);
+       return rc;
 }
 
 /* This is the function which gets called during socket creation to