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

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Message-Id: <20250430-vsock-linger-v3-1-ddbe73b53457@rbox.co>
Date: Wed, 30 Apr 2025 11:10:27 +0200
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>, 
 "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>
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
 Michal Luczaj <mhal@...x.co>
Subject: [PATCH net-next v3 1/4] vsock/virtio: Linger on unsent data

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;

 		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