vsock: Move lingering logic to af_vsock core

Lingering should be transport-independent in the long run. In preparation
for supporting other transports, as well as the linger on shutdown(), move
code to core.

Generalize by querying vsock_transport::unsent_bytes(), guard against the
callback being unimplemented. Do not pass sk_lingertime explicitly. Pull
SOCK_LINGER check into vsock_linger().

Flatten the function. Remove the nested block by inverting the condition:
return early on !timeout.

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250522-vsock-linger-v6-2-2ad00b0e447e@rbox.co
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: mmhal

include/net/af_vsock.h

@@ -221,6 +221,7 @@ void vsock_for_each_connected_socket(struct vsock_transport *transport,
 				     void (*fn)(struct sock *sk));
 int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk);
 bool vsock_find_cid(unsigned int cid);
+void vsock_linger(struct sock *sk);
 
 /**** TAP ****/
 

net/vmw_vsock/af_vsock.c

@@ -1013,6 +1013,39 @@ static int vsock_getname(struct socket *sock,
 	return err;
 }
 
+void vsock_linger(struct sock *sk)
+{
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	ssize_t (*unsent)(struct vsock_sock *vsk);
+	struct vsock_sock *vsk = vsock_sk(sk);
+	long timeout;
+
+	if (!sock_flag(sk, SOCK_LINGER))
+		return;
+
+	timeout = sk->sk_lingertime;
+	if (!timeout)
+		return;
+
+	/* Transports must implement `unsent_bytes` if they want to support
+	 * SOCK_LINGER through `vsock_linger()` since we use it to check when
+	 * the socket can be closed.
+	 */
+	unsent = vsk->transport->unsent_bytes;
+	if (!unsent)
+		return;
+
+	add_wait_queue(sk_sleep(sk), &wait);
+
+	do {
+		if (sk_wait_event(sk, &timeout, unsent(vsk) == 0, &wait))
+			break;
+	} while (!signal_pending(current) && timeout);
+
+	remove_wait_queue(sk_sleep(sk), &wait);
+}
+EXPORT_SYMBOL_GPL(vsock_linger);
+
 static int vsock_shutdown(struct socket *sock, int mode)
 {
 	int err;

net/vmw_vsock/virtio_transport_common.c

@@ -1191,25 +1191,6 @@ static void virtio_transport_remove_sock(struct vsock_sock *vsk)
 	vsock_remove_sock(vsk);
 }
 
-static void virtio_transport_wait_close(struct sock *sk, long timeout)
-{
-	if (timeout) {
-		DEFINE_WAIT_FUNC(wait, woken_wake_function);
-		struct vsock_sock *vsk = vsock_sk(sk);
-
-		add_wait_queue(sk_sleep(sk), &wait);
-
-		do {
-			if (sk_wait_event(sk, &timeout,
-					  virtio_transport_unsent_bytes(vsk) == 0,
-					  &wait))
-				break;
-		} while (!signal_pending(current) && timeout);
-
-		remove_wait_queue(sk_sleep(sk), &wait);
-	}
-}
-
 static void virtio_transport_cancel_close_work(struct vsock_sock *vsk,
 					       bool cancel_timeout)
 {
@@ -1279,8 +1260,8 @@ static bool virtio_transport_close(struct vsock_sock *vsk)
 	if ((sk->sk_shutdown & SHUTDOWN_MASK) != SHUTDOWN_MASK)
 		(void)virtio_transport_shutdown(vsk, SHUTDOWN_MASK);
 
-	if (sock_flag(sk, SOCK_LINGER) && !(current->flags & PF_EXITING))
-		virtio_transport_wait_close(sk, sk->sk_lingertime);
+	if (!(current->flags & PF_EXITING))
+		vsock_linger(sk);
 
 	if (sock_flag(sk, SOCK_DONE)) {
 		return true;