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

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Date:   Mon, 8 Aug 2022 12:23:35 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
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>,
        Bryan Tan <bryantan@...are.com>,
        Vishnu Dasa <vdasa@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        Krasnov Arseniy <oxffffaa@...il.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v3 1/9] vsock: SO_RCVLOWAT transport set callback

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@...rdevices.ru>
>---
> 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