Re: [RFC PATCH v3 03/13] af_vsock: implement SEQPACKET rx loop

Stefano Garzarella
2021-01-28T16:57:09Z

On Mon, Jan 25, 2021 at 02:12:36PM +0300, Arseny Krasnov wrote:
>This adds receive loop for SEQPACKET. It looks like receive loop for
>SEQPACKET, 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>
>---
> include/net/af_vsock.h | 5 ++
> net/vmw_vsock/af_vsock.c | 102 ++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 106 insertions(+), 1 deletion(-)
>
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index b1c717286993..46073842d489 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -135,6 +135,11 @@ struct vsock_transport {
> bool (*stream_is_active)(struct vsock_sock *);
> bool (*stream_allow)(u32 cid, u32 port);
>
>+ /* SEQ_PACKET. */
>+ size_t (*seqpacket_seq_get_len)(struct vsock_sock *);
>+ ssize_t (*seqpacket_dequeue)(struct vsock_sock *, struct msghdr *,
>+ size_t len, int flags);
>+
> /* 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 524df8fc84cd..3b266880b7c8 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -2006,7 +2006,107 @@ static int __vsock_stream_recvmsg(struct sock *sk, struct msghdr *msg,
> static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr *msg,
> size_t len, int flags)
> {
>- return -1;
>+ const struct vsock_transport *transport;
>+ const struct iovec *orig_iov;
>+ unsigned long orig_nr_segs;
>+ ssize_t dequeued_total = 0;
>+ struct vsock_sock *vsk;
>+ size_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->msg_flags &= ~MSG_EOR;

Maybe add a comment about why we need to clear MSG_EOR.

>+ orig_nr_segs = msg->msg_iter.nr_segs;
>+ orig_iov = msg->msg_iter.iov;
>+
>+ while (1) {
>+ ssize_t dequeued;
>+ s64 ready;
>+
>+ prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
>+ ready = vsock_stream_has_data(vsk);
>+
>+ if (ready == 0) {
>+ if (vsock_wait_data(sk, &wait, timeout, NULL, 0)) {
>+ /* In case of any loop break(timeout, signal
>+ * interrupt or shutdown), we report user that
>+ * nothing was copied.
>+ */
>+ dequeued_total = 0;
>+ break;
>+ }
>+ continue;
>+ }
>+
>+ finish_wait(sk_sleep(sk), &wait);
>+
>+ if (ready < 0) {
>+ err = -ENOMEM;
>+ goto out;
>+ }
>+
>+ if (dequeued_total == 0) {
>+ record_len =
>+ transport->seqpacket_seq_get_len(vsk);
>+
>+ if (record_len == 0)
>+ continue;
>+ }
>+
>+ /* 'msg_iter.count' is number of unused bytes in iov.
>+ * On every copy to iov iterator it is decremented at
>+ * size of data.
>+ */
>+ dequeued = transport->seqpacket_dequeue(vsk, msg,
>+ msg->msg_iter.count, flags);
^
Is this needed or 'msg' can be
used in the transport?
>+
>+ if (dequeued < 0) {
>+ dequeued_total = 0;
>+
>+ if (dequeued == -EAGAIN) {
>+ iov_iter_init(&msg->msg_iter, READ,
>+ orig_iov, orig_nr_segs,
>+ len);
>+ msg->msg_flags &= ~MSG_EOR;
>+ continue;

Why we need to reset MSG_EOR here?

>+ }
>+
>+ err = -ENOMEM;
>+ break;
>+ }
>+
>+ dequeued_total += dequeued;
>+
>+ if (dequeued_total >= record_len)
>+ break;
>+ }

Maybe a new line here.

>+ if (sk->sk_err)
>+ err = -sk->sk_err;
>+ else if (sk->sk_shutdown & RCV_SHUTDOWN)
>+ err = 0;
>+
>+ if (dequeued_total > 0) {
>+ /* User sets MSG_TRUNC, so return real length of
>+ * packet.
>+ */
>+ if (flags & MSG_TRUNC)
>+ err = record_len;
>+ else
>+ err = len - msg->msg_iter.count;
>+
>+ /* Always set MSG_TRUNC if real length of packet is
>+ * bigger that user buffer.

s/that/than

>+ */
>+ if (record_len > len)
>+ msg->msg_flags |= MSG_TRUNC;
>+ }
>+out:
>+ return err;
> }
>
> static int
>--
>2.25.1
>