Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK_SEQPACKET

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On Tue, Jun 27, 2023 at 07:34:29AM +0300, Arseniy Krasnov wrote:


On 26.06.2023 19:28, Stefano Garzarella wrote:
On Sun, Jun 18, 2023 at 09:24:49AM +0300, Arseniy Krasnov wrote:
This adds support of MSG_PEEK flag for SOCK_SEQPACKET type of socket.
Difference with SOCK_STREAM is that this callback returns either length
of the message or error.

Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
---
net/vmw_vsock/virtio_transport_common.c | 63 +++++++++++++++++++++++--
1 file changed, 60 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 2ee40574c339..352d042b130b 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -460,6 +460,63 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
    return err;
}

+static ssize_t
+virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
+                   struct msghdr *msg)
+{
+    struct virtio_vsock_sock *vvs = vsk->trans;
+    struct sk_buff *skb;
+    size_t total, len;
+
+    spin_lock_bh(&vvs->rx_lock);
+
+    if (!vvs->msg_count) {
+        spin_unlock_bh(&vvs->rx_lock);
+        return 0;
+    }
+
+    total = 0;
+    len = msg_data_left(msg);
+
+    skb_queue_walk(&vvs->rx_queue, skb) {
+        struct virtio_vsock_hdr *hdr;
+
+        if (total < len) {
+            size_t bytes;
+            int err;
+
+            bytes = len - total;
+            if (bytes > skb->len)
+                bytes = skb->len;
+
+            spin_unlock_bh(&vvs->rx_lock);
+
+            /* sk_lock is held by caller so no one else can dequeue.
+             * Unlock rx_lock since memcpy_to_msg() may sleep.
+             */
+            err = memcpy_to_msg(msg, skb->data, bytes);
+            if (err)
+                return err;
+
+            spin_lock_bh(&vvs->rx_lock);
+        }
+
+        total += skb->len;
+        hdr = virtio_vsock_hdr(skb);
+
+        if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) {
+            if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOR)
+                msg->msg_flags |= MSG_EOR;
+
+            break;
+        }
+    }
+
+    spin_unlock_bh(&vvs->rx_lock);
+
+    return total;

Should we return the minimum between total and len?

I guess no, because seqpacket dequeue callback always returns length of message,
then, in af_vsock.c we return either number of bytes read or length of message
depending on MSG_TRUNC flags.

Right! We should always return the total lenght of the packet.

Thanks,
Stefano


Thanks, Arseniy


Thanks,
Stefano

+}
+
static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
                         struct msghdr *msg,
                         int flags)
@@ -554,9 +611,9 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
                   int flags)
{
    if (flags & MSG_PEEK)
-        return -EOPNOTSUPP;
-
-    return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
+        return virtio_transport_seqpacket_do_peek(vsk, msg);
+    else
+        return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
}
EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);

-- 
2.25.1







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