Re: [RFC PATCH v8 04/19] af_vsock: implement SEQPACKET receive loop

Stefano Garzarella
2021-04-21T08:38:10Z

On Tue, Apr 13, 2021 at 03:42:47PM +0300, Arseny Krasnov wrote:
>This adds receive loop for SEQPACKET. It looks like receive loop for
>STREAM, but there is a little bit difference:
>1) It doesn't call notify callbacks.
>2) It doesn't care about 'SO_SNDLOWAT' and 'SO_RCVLOWAT' values, because
> there is no sense for these values in SEQPACKET case.
>3) It waits until whole record is received or error is found during
> receiving.
>4) It processes and sets 'MSG_TRUNC' flag.
>
>So to avoid extra conditions for two types of socket inside one loop, two
>independent functions were created.
>
>Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>---
>v7 -> v8:
> - Length of message is now not returned by callback, it returns only
> length of data read by each call.
> - Previous case, when EAGAIN is return and dequeue loop restarted now
> removed(in this simplified version we consider that message could not
> be corrupted).
> - MSG_TRUNC in input flags is now handled by callback.
>
> include/net/af_vsock.h | 4 +++
> net/vmw_vsock/af_vsock.c | 66 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 69 insertions(+), 1 deletion(-)
>
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index b1c717286993..5175f5a52ce1 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -135,6 +135,10 @@ struct vsock_transport {
> bool (*stream_is_active)(struct vsock_sock *);
> bool (*stream_allow)(u32 cid, u32 port);
>
>+ /* SEQ_PACKET. */
>+ ssize_t (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
>+ int flags, bool *msg_ready);
>+
> /* Notification. */
> int (*notify_poll_in)(struct vsock_sock *, size_t, bool *);
> int (*notify_poll_out)(struct vsock_sock *, size_t, bool *);
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index c4f6bfa1e381..d9fb4f9a3063 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -1974,6 +1974,67 @@ static int __vsock_stream_recvmsg(struct sock *sk, struct msghdr *msg,
> return err;
> }
>
>+static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr *msg,
>+ size_t len, int flags)
>+{
>+ const struct vsock_transport *transport;
>+ bool msg_ready;
>+ struct vsock_sock *vsk;
>+ ssize_t record_len;
>+ long timeout;
>+ int err = 0;
>+ DEFINE_WAIT(wait);
>+
>+ vsk = vsock_sk(sk);
>+ transport = vsk->transport;
>+
>+ timeout = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
>+ msg_ready = false;
>+ record_len = 0;
>+
>+ while (1) {
>+ ssize_t tmp_record_len;

Maybe better a name like `partial_len`, `fragment_len`, or just `read`.

>+
>+ if (vsock_wait_data(sk, &wait, timeout, NULL, 0) <= 0) {
>+ /* In case of any loop break(timeout, signal
>+ * interrupt or shutdown), we report user that
>+ * nothing was copied.
>+ */
>+ err = 0;
>+ break;
>+ }
>+
>+ tmp_record_len = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready);

I think we can avoid to pass 'flags' down to the transports.

We can require that seqpacket_dequeue() should always return the real
size of the packet received, and then check below if 'MSG_TRUNC' was
set...

>+
>+ if (tmp_record_len < 0) {
>+ err = -ENOMEM;
>+ break;
>+ }
>+
>+ record_len += tmp_record_len;
>+
>+ if (msg_ready)
>+ break;
>+ }
>+
>+ if (sk->sk_err)
>+ err = -sk->sk_err;
>+ else if (sk->sk_shutdown & RCV_SHUTDOWN)
>+ err = 0;
>+
>+ if (msg_ready && err == 0) {
>+ err = record_len;
>+
>+ /* Always set MSG_TRUNC if real length of packet is
>+ * bigger than user's buffer.
>+ */

...here:
if (flags & MSG_TRUNC && record_len > len)

>+ if (record_len > len)
>+ msg->msg_flags |= MSG_TRUNC;
>+ }
>+
>+ return err;
>+}
>+
> static int
> vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> int flags)
>@@ -2029,7 +2090,10 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> goto out;
> }
>
>- err = __vsock_stream_recvmsg(sk, msg, len, flags);
>+ if (sk->sk_type == SOCK_STREAM)
>+ err = __vsock_stream_recvmsg(sk, msg, len, flags);
>+ else
>+ err = __vsock_seqpacket_recvmsg(sk, msg, len, flags);
>
> out:
> release_sock(sk);
>-- )
>2.25.1
>