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    SubjectRe: [RFC PATCH v2 5/9] vsock: SO_RCVLOWAT transport set callback
    Date
    On 27.07.2022 15:24, Stefano Garzarella wrote:
    > On Mon, Jul 25, 2022 at 08:05:28AM +0000, Arseniy Krasnov wrote:
    >> This adds transport specific callback for SO_RCVLOWAT, because in some
    >> transports it may be difficult to know current available number of bytes
    >> ready to read. Thus, when SO_RCVLOWAT is set, transport may reject it.
    >>
    >> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
    >> ---
    >> include/net/af_vsock.h   |  1 +
    >> net/vmw_vsock/af_vsock.c | 19 +++++++++++++++++++
    >> 2 files changed, 20 insertions(+)
    >>
    >> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
    >> index f742e50207fb..eae5874bae35 100644
    >> --- a/include/net/af_vsock.h
    >> +++ b/include/net/af_vsock.h
    >> @@ -134,6 +134,7 @@ struct vsock_transport {
    >>     u64 (*stream_rcvhiwat)(struct vsock_sock *);
    >>     bool (*stream_is_active)(struct vsock_sock *);
    >>     bool (*stream_allow)(u32 cid, u32 port);
    >> +    int (*set_rcvlowat)(struct vsock_sock *, int);
    >>
    >>     /* SEQ_PACKET. */
    >>     ssize_t (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
    >> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
    >> index 63a13fa2686a..b7a286db4af1 100644
    >> --- a/net/vmw_vsock/af_vsock.c
    >> +++ b/net/vmw_vsock/af_vsock.c
    >> @@ -2130,6 +2130,24 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
    >>     return err;
    >> }
    >>
    >> +static int vsock_set_rcvlowat(struct sock *sk, int val)
    >> +{
    >> +    const struct vsock_transport *transport;
    >> +    struct vsock_sock *vsk;
    >> +    int err = 0;
    >> +
    >> +    vsk = vsock_sk(sk);
    >> +    transport = vsk->transport;
    >
    > `transport` can be NULL if the user call SO_RCVLOWAT before we assign it, so we should check it.
    Ack
    >
    > I think if the transport implements `set_rcvlowat`, maybe we should set there sk->sk_rcvlowat, so I would do something like that:
    >
    >     if (transport && transport->set_rcvlowat)
    >         err = transport->set_rcvlowat(vsk, val);
    >     else
    >         WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
    >
    >     return err;
    >
    > In addition I think we should check that val does not exceed vsk->buffer_size, something similar of what tcp_set_rcvlowat() does.
    >
    Ack
    > Thanks,
    > Stefano
    >

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