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>

1 files changed, 34 insertions, 1 deletions

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index cf6dcc908b88..6a691d84aef4 100644
--- 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