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Date:   Wed, 27 Jul 2022 14:24:17 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Cc:     "David S. Miller" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "kys@microsoft.com" <kys@microsoft.com>,
        "haiyangz@microsoft.com" <haiyangz@microsoft.com>,
        "sthemmin@microsoft.com" <sthemmin@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Krasnov Arseniy <oxffffaa@gmail.com>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
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        kernel <kernel@sberdevices.ru>
Subject: Re: [RFC PATCH v2 5/9] vsock: SO_RCVLOWAT transport set callback
Message-ID: <20220727122417.jvdfjnuybk3mwxkq@sgarzare-redhat>
References: <19e25833-5f5c-f9b9-ac0f-1945ea17638d@sberdevices.ru>
 <8baa2e3a-af6b-c0fe-9bfb-7cf89506474a@sberdevices.ru>
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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.

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.

Thanks,
Stefano