Re: [RFC PATCH v3 1/9] vsock: SO_RCVLOWAT transport set callback

[Stefano Garzarella]

On Wed, Aug 03, 2022 at 01:51:05PM +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@xxxxxxxxxxxxxx>
> ---
> include/net/af_vsock.h   |  1 +
> net/vmw_vsock/af_vsock.c | 25 +++++++++++++++++++++++++
> 2 files changed, 26 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);

checkpatch suggests to add identifier names. For some we put them in, 
for others we didn't, but I suggest putting them in for the new ones 
because I think it's clearer too.

WARNING: function definition argument 'struct vsock_sock *' should also 
have an identifier name
#25: FILE: include/net/af_vsock.h:137:
+	int (*set_rcvlowat)(struct vsock_sock *, int);

WARNING: function definition argument 'int' should also have an identifier name
#25: FILE: include/net/af_vsock.h:137:
+	int (*set_rcvlowat)(struct vsock_sock *, int);

total: 0 errors, 2 warnings, 0 checks, 44 lines checked

> 	/* 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 f04abf662ec6..016ad5ff78b7 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -2129,6 +2129,30 @@ 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);
> +
> +	if (val > vsk->buffer_size)
> +		return -EINVAL;
> +
> +	transport = vsk->transport;
> +
> +	if (!transport)
> +		return -EOPNOTSUPP;

I don't know whether it is better in this case to write it in 
sk->sk_rcvlowat, maybe we can return EOPNOTSUPP only when the trasport 
is assigned and set_rcvlowat is not defined. This is because usually the 
options are set just after creation, when the transport is practically 
unassigned.

I mean something like this:

        if (transport) {
                if (transport->set_rcvlowat)
                        return transport->set_rcvlowat(vsk, val);
                else
                        return -EOPNOTSUPP;
        }

        WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);

        return 0;

> +
> +	if (transport->set_rcvlowat)
> +		err = transport->set_rcvlowat(vsk, val);
> +	else
> +		WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
> +
> +	return err;
> +}
> +
> static const struct proto_ops vsock_stream_ops = {
> 	.family = PF_VSOCK,
> 	.owner = THIS_MODULE,
> @@ -2148,6 +2172,7 @@ static const struct proto_ops vsock_stream_ops = {
> 	.recvmsg = vsock_connectible_recvmsg,
> 	.mmap = sock_no_mmap,
> 	.sendpage = sock_no_sendpage,
> +	.set_rcvlowat = vsock_set_rcvlowat,
> };
>
> static const struct proto_ops vsock_seqpacket_ops = {
> --
> 2.25.1