[PATCH] vsock/virtio: add support for MSG_PEEK

[Matias Ezequiel Vara Larsen]

This patch adds support for MSG_PEEK. In such a case, packets are not
removed from the rx_queue and credit updates are not sent.

Signed-off-by: Matias Ezequiel Vara Larsen <matiasev...@gmail.com>
---
 net/vmw_vsock/virtio_transport_common.c | 50 +++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c 
b/net/vmw_vsock/virtio_transport_common.c
index 94cc0fa..938f2ed 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -264,6 +264,50 @@ static int virtio_transport_send_credit_update(struct 
vsock_sock *vsk,
 }
 
 static ssize_t
+virtio_transport_stream_do_peek(struct vsock_sock *vsk,
+                               struct msghdr *msg,
+                               size_t len)
+{
+       struct virtio_vsock_sock *vvs = vsk->trans;
+       struct virtio_vsock_pkt *pkt;
+       size_t bytes, total = 0;
+       int err = -EFAULT;
+
+       spin_lock_bh(&vvs->rx_lock);
+
+       list_for_each_entry(pkt, &vvs->rx_queue, list) {
+               if (total == len)
+                       break;
+
+               bytes = len - total;
+               if (bytes > pkt->len - pkt->off)
+                       bytes = pkt->len - pkt->off;
+
+               /* sk_lock is held by caller so no one else can dequeue.
+                * Unlock rx_lock since memcpy_to_msg() may sleep.
+                */
+               spin_unlock_bh(&vvs->rx_lock);
+
+               err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
+               if (err)
+                       goto out;
+
+               spin_lock_bh(&vvs->rx_lock);
+
+               total += bytes;
+       }
+
+       spin_unlock_bh(&vvs->rx_lock);
+
+       return total;
+
+out:
+       if (total)
+               err = total;
+       return err;
+}
+
+static ssize_t
 virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
                                   struct msghdr *msg,
                                   size_t len)
@@ -330,9 +374,9 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
                                size_t len, int flags)
 {
        if (flags & MSG_PEEK)
-               return -EOPNOTSUPP;
-
-       return virtio_transport_stream_do_dequeue(vsk, msg, len);
+               return virtio_transport_stream_do_peek(vsk, msg, len);
+       else
+               return virtio_transport_stream_do_dequeue(vsk, msg, len);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_stream_dequeue);
 
-- 
2.7.4