linux-kernel - Re: [PATCH net-next v3 1/4] vsock/virtio: Linger on unsent data

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Message-ID: <x3kkxnrqujqjkrtptr2qdd3227ncof2vb7jbrcg3aibvwjfqxa@hbinpxjuk3qe>
Date: Wed, 30 Apr 2025 11:26:55 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
Cc: "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Stefan Hajnoczi <stefanha@...hat.com>, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/4] vsock/virtio: Linger on unsent data

On Wed, Apr 30, 2025 at 11:10:27AM +0200, Michal Luczaj wrote:
>Currently vsock's lingering effectively boils down to waiting (or timing
>out) until packets are consumed or dropped by the peer; be it by receiving
>the data, closing or shutting down the connection.
>
>To align with the semantics described in the SO_LINGER section of man
>socket(7) and to mimic AF_INET's behaviour more closely, change the logic
>of a lingering close(): instead of waiting for all data to be handled,
>block until data is considered sent from the vsock's transport point of
>view. That is until worker picks the packets for processing and decrements
>virtio_vsock_sock::bytes_unsent down to 0.
>
>Note that (some interpretation of) lingering was always limited to
>transports that called virtio_transport_wait_close() on transport release.
>This does not change, i.e. under Hyper-V and VMCI no lingering would be
>observed.
>
>The implementation does not adhere strictly to man page's interpretation of
>SO_LINGER: shutdown() will not trigger the lingering. This follows AF_INET.
>
>Signed-off-by: Michal Luczaj <mhal@...x.co>
>---
> net/vmw_vsock/virtio_transport_common.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 7f7de6d8809655fe522749fbbc9025df71f071bd..49c6617b467195ba385cc3db86caa4321b422d7a 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1196,12 +1196,16 @@ static void virtio_transport_wait_close(struct sock *sk, long timeout)
> {
> 	if (timeout) {
> 		DEFINE_WAIT_FUNC(wait, woken_wake_function);
>+		ssize_t (*unsent)(struct vsock_sock *vsk);
>+		struct vsock_sock *vsk = vsock_sk(sk);
>+
>+		unsent = vsk->transport->unsent_bytes;

Just use `virtio_transport_unsent_bytes`, we don't need to be generic on 
transport here.

>
> 		add_wait_queue(sk_sleep(sk), &wait);
>
> 		do {
>-			if (sk_wait_event(sk, &timeout,
>-					  sock_flag(sk, SOCK_DONE), &wait))
>+			if (sk_wait_event(sk, &timeout, unsent(vsk) == 0,
>+					  &wait))
> 				break;
> 		} while (!signal_pending(current) && timeout);
>
>
>-- 
>2.49.0
>