netdev - Re: [RFC PATCH v2 5/9] vsock: SO_RCVLOWAT transport set callback

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Date:   Thu, 28 Jul 2022 06:06:41 +0000
From:   Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To:     Stefano Garzarella <sgarzare@...hat.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
        "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "Dexuan Cui" <decui@...rosoft.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Krasnov Arseniy" <oxffffaa@...il.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v2 5/9] vsock: SO_RCVLOWAT transport set callback

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@...rdevices.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
>